Title: Leucine-based motif and
United States Patent: 7,393,925
Issued; July 1, 2008
Inventors: Steward; Lance
E. (Irvine, CA), Herrington; Todd M. (Irvine, CA), Aoki; Kei Roger (Coto
De Caza, CA)
Assignee: Allergan, Inc.
Appl. No.: 11/039,268
Filed: January 19, 2005
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Modified neurotoxin comprising neurotoxin
including structural modification, wherein the structural modification
alters the biological persistence, preferably the biological half-life, of
the modified neurotoxin relative to an identical neurotoxin without the
structural modification. The structural modification includes addition or
deletion of a leucine-based motif or parts thereof. In one embodiment,
methods of making the modified neurotoxin include using recombinant
techniques. In another embodiment, methods of using the modified
neurotoxin to treat biological disorders include treating autonomic
disorders, neuromuscular disorders or pains.
Description of the
The present invention meets this need and provides for non serotype A
botulinum toxins with enhanced persistence and BoNT/A with reduced
persistence and methods for preparing such toxins.
In one broad embodiment of the invention, a modified neurotoxin is formed
from a neurotoxin which includes a structural modifcation. The structural
modification is able to alter the biological persistence of the neurotoxin.
In one embodiment, the structural modification includes fusing a biological
persistence enhancing component with a neurotoxin. The biological
persistence enhancing component increases the duration of the inhibitory
effect of the modified neurotoxin intracellularly. Preferably, the
biological persistence enhancing component is a leucine-based motif.
Without wishing to be limited by any particular theory or mechanism of
operation, it is believed that the leucine-based motif enhances the
persistence of a neurotoxin by increasing its biological half-life. For
example, it is known that BoNT/A has a very long biological persistence.
Keller et al., FEBS Letters, 456:137-142 (1999), investigated to determine
whether the persistence of BoNT/A is due to a depressed synthesis of SNAP-25
to replace the cleaved ones, or is due to the stability of the light chain
intracellularly. Keller et al. found that the major factor limiting cellular
recovery is the prolonged stability of toxin, or prolonged half-life.
Furthermore, without wishing to be limited by any particular theory or
mechanism of operation, it is believed that the leucine-based motif located
on the light chain, or the third amino acid sequence region, of BoNT/A, and
not on any other serotypes, is responsible for the prolonged half-life of
A leucine-based motif is often found on the carboxyl termini of several
membrane receptors and vesicular neurotransmitter transporter and it
apparently plays a crucial role in vesicle/membrane trafficking. Liu et al.
Trends Cell Biol, 9:356-363 (1999); Tan et al. J Biol Chem, 273:17351-17360
(1998); Dietrich et al. J. Cell Bio, 138:271-281 (1997); Shin et al. J Biol
Chem, 266:10658-10665 (1991) and Geisler et al. J Biol Chem, 273:21316-21323
(1998). More specifically, the leuine-based motif is found in a
membrane-proximal, cytoplasmic, carboxylic terminal tail of a membrane-bound
receptor or transporter protein. It has been demonstrated that adaptor
proteins that are highly concentrated at clathrin coated pits bind to the
leucine-based motif and that disruption of this motif disrupts endocytosis
of the motif-containing protein. Tan et al. J Biol Chem, 273:17351-17360
(1998); Dietrich et al. J. Cell Bio, 138:271-281 (1997) and Shin et al. J
Biol Chem, 266:10658-10665 (1991). Furthermore, addition of the leucine-based
motif to the carboxyl terminus of the plasma membrane protein Tac resulted
in endocytosis of the chimera, suggesting that the motif is sufficient for
targeted endocytosis. Tan et al. Supra.
The leucine-based motif located on the light chain of BoNT/A may cause the
light chain to localize at the membranes, similarly to how membrane-bound
receptor or transporter protein are localized at the membranes described
above. Localization of the light chain to the membrane may protect and
preserve the light chain, and the heavy chain if it is still attached, from
being removed and/or degraded by the intracellular cleaning processes,
thereby rendering it a long biological half-life. For example, intracellular
autophagosomes are responsible for cleaning the cytoplasm by engulfing, and
thereafter degrading, free floating foreign substances in the cytoplasm.
Erdal et al. Naunyn Schmiedebergs Acrch Pharmacol, 351:67-78 (1995). Since
the leucine-based motif provides an anchor for the light chain, and the
heavy chain if it is still attached, it would be difficult for the
autophagosomes to remove and engulf the light chain from the cytoplasm. Thus
the light chain remains in the cytoplasm to continue exerting its inhibitory
effects on vesicular exocytosis of neurotransmitters.
In another embodiment, the leucine-based motif located on the light chain of
BoNT/A is removed in its entirety or in parts. This modified neurotoxin
effectively has a shortened the biological persistence. Preferably, this
modified neurotoxin has a decreased half-life.
This invention also provide for methods of producing modified neurotoxins.
Additionally, this invention provide for methods of using the modified
neurotoxins to treat biological disorders.
The present invention is based upon the discovery that the biological
persistence of a neurotoxin may be altered by structurally modifying the
neurotoxin. In other words, a modified neurotoxin with an altered biological
persistence may be formed from a neurotoxin containing or including a
structural modification. In one embodiment, the structural modification
includes the fusing a biological persistence enhancing component to the
primary structure of a neurotoxin to enhance its biological persistence. In
a preferred embodiment, the biological persistence enhancing component is a
leucine-based motif. Preferably, the biological persistence enhancing
component enhances the biological half-life of the modified neurotoxin. More
preferably, the biological half-life of the modified neurotoxin is enhanced
by about 10%. Even more preferably, the biological half-life of the modified
neurotoxin is enhanced by about 100%. Generally speaking, the modified
neurotoxin has a biological persistence of about 20% to 300% more than an
identical neurotoxin without the structural modification. That is, for
example, the modified neurotoxin including the biological persistence
enhancing component is able to cause a substantial inhibition of
acetylcholine release from a nerve terminal for about 20% to about 300%
longer than a neurotoxin that is not modified.
In a broad embodiment of the present invention, a leucine-based motif is an
oligomer of seven amino acids. The oligomer is organized in to two groups.
The first five amino acids starting from the amino terminal of the leucine-based
motif form a "quintet of amino acids." The two amino acids immediately
following the quintet of amino acids form a "duplet of amino acids." In a
preferred embodiment, the duplet of amino acids is located at the carboxyl
terminal region of the leucine-based motif. In another preferred embodiment,
the quintet of amino acids includes at least one acidic amino acid selected
from a group consisting of a glutamate and an aspartate.
The duplet of amino acid includes at least one hydrophobic amino acid, for
example leucine, isoleucine, methionine, alanine, phenylalanine, tryptophan,
valine or tyrosine. Preferably, the duplet of amino acid is a
leucine-leucine, a leucine-isoleucine, an isoleucine-leucine or an
isoleucine-isoleucine. Even more preferably, the duplet is a leucine-leucine.
In one embodiment, the leucine-based motif is xDxxxLL (SEQ ID NO: 1),
wherein x can be any amino acids. In another embodiment, the leucine-based
motif is xExxxLL (SEQ ID NO: 2), wherein E is glutamic acid. In another
embodiment, the duplet of amino acids can include an isoleucine or a
methionine, forming xDxxxLl (SEQ ID NO: 3) or xDxxxLM (SEQ ID NO: 4),
respectively. Additionally, the aspartic acid, D, can be replaced by a
glutamic acid, E, to form xExxxLl (SEQ ID NO: 5) and xExxxLM (SEQ ID NO: 6).
In a preferred embodiment, the leucine-based motif is SEQ ID NO: 7.
In another embodiment, the quintet of amino acids comprises at least one
hydroxyl containing amino acid, for example a serine, a threonine or a
tyrosine. Preferably, the hydroxyl containing amino acid can be
phosphorylated. More preferably, the hydroxyl containing amino acid is a
serine which can be phosphorylated to allow for the binding of adaptor
Although non-modified amino acids are provided as examples, a modified amino
acid is also contemplated to be within the scope of this invention. For
example, leucine-based motif may include a halogenated, preferably,
Various leucine-based motif are found in various species. A list of possible
leucine-based motif derived from the various species that may be used in
accordance with this invention is shown in Table 1 (see Original Patent).
This list is not intended to be limiting.
VMAT is vesicular monoamine transporter; VACht is vesicular acetylcholine
transporter. Italicized serine residues are potential sites of
The modified neurotoxin may be formed from any neurotoxin. Preferably, the
neurotoxin used is a Clostridial neurotoxin. A Clostridial neurotoxin
comprises a polypeptide having three amino acid sequence regions. The first
amino acid sequence region includes a neuronal binding moiety which is
substantially completely derived from a neurotoxin selected from a group
consisting of beratti toxin; butyricum toxin; tetani toxin; BoNT/A, B,
C.sub.1, D, E, F, and G. Preferably, the first amino acid sequence region is
derived from the carboxyl terminal region of a toxin heavy chain, H.sub.C.
The second amino acid sequence region is effective to translocate the
polypeptide or a part thereof across an endosome membrane into the cytoplasm
of a neuron. In one embodiment, the second amino acid sequence region of the
polypeptide comprises an amine terminal of a heavy chain, H.sub.N, derived
from a neurotoxin selected from a group consisting of beratti toxin;
butyricum toxin; tetani toxin; BoNT/A, B, C.sub.1, D, E, F, and G.
The third amino acid sequence region has therapeutic activity when it is
released into the cytoplasm of a target cell or neuron. In one embodiment,
the third amino acid sequence region of the polypeptide comprises a toxin
light chain, L, derived from a neurotoxin selected from a group consisting
of beratti toxin; butyricum toxin; tetani toxin; BoNT/A, B, C.sub.1, D, E,
F, and G.
The Clostridial neurotoxin may be a hybrid neurotoxin. For example, each of
the neurotoxin's amino acid sequence regions may be derived from a different
Clostridial neurotoxin serotype. For example, in one embodiment, the
polypeptide comprises a first amino acid sequence region derived from the
H.sub.C of the tetani toxin, a second amino acid sequence region derived
from the H.sub.N of BoNt/B, and a third amino acid sequence region derived
from the L chain of botulinum serotype E. All other possible combinations
are included within the scope of the present invention.
Alternatively, all three of the amino acid sequence regions of the
Clostridial neurotoxin may be from the same species and same serotype. If
all three amino acid sequence regions of the neurotoxin are from the same
Clostridial neurotoxin species and serotype, the neurotoxin will be referred
to by the species and serotype name. For example, a neurotoxin polypeptide
may have its first, second and third amino acid sequence regions derived
from BoNT/E. In which case, the neurotoxin is referred as BoNT/E.
Additionally, each of the three amino acid sequence regions may be modified
from the naturally occurring sequence from which they are derived. For
example, the amino acid sequence region may have at least one or more amino
acid may be added or deleted as compared to the naturally occurring
The biological persistence enhancing component, preferably the leucine-based
motif, may be fused with any of the above described neurotoxin to form a
modified neurotoxin with an enhanced biological persistence. "Fusing" as
used in the context of this invention includes covalently adding to or
covalently inserting in between a primary structure of a neurotoxin.
Preferably, the biological persistence enhancing component is added to a
Clostridial neurotoxin which does not have a leucine-based motif in its
primary structure. For example, in one embodiment, the leucine-based motif
is fused with a hybrid neurotoxin, wherein the third amino acid sequence is
not derived from botulinum serotype A. In another embodiment, the leucine-based
motif is fused with a BoNt/E.
In one embodiment, the leucine-based motif is fused with the third amino
acid sequence region of the neurotoxin. In a preferred embodiment, the
leucine-based motif is fused with the region towards the carboxylic terminal
of the third amino acid sequence region. More preferably, the leucine-based
motif is fused with the carboxylic terminal of the third region of a
neurotoxin. Even more preferably, the leucine-based motif is fused with the
carboxylic terminal of the third region of BoNt/E.
In another embodiment, the structural modification of a neurotoxin which has
a preexisting leucine-based motif includes deleting one or more amino acids
from the leucine-based motif. Alternatively, a modified neurotoxin includes
a structural modification which results in a neurotoxin with one or more
amino acids absent from the leucine-based motif. The removal of one or more
amino acids from the preexisting leucine-based motif is effective to reduce
the biological persistence of a modified neurotoxin. More preferably, the
deletion of one or more amino acids from the leucine-based motif of BoNT/A
reduces the biological half-life of the modified neurotoxin.
In one broad aspect of the present invention, a method is provided for
treating a biological disorder using a modified neurotoxin. The treatments
may include treating neuromuscular disorders, autonomic nervous system
disorders and pain.
The neuromuscular disorders and conditions that may be treated with a
modified neurotoxin include: for example, strabismus, blepharospasm,
spasmodic torticollis (cervical dystonia), oromandibular dystonia and
spasmodic dysphonia (largyngeal dystonia).
For example, Borodic U.S. Pat. No. 5,053,005 discloses methods for treating
juvenile spinal curvature, i.e. scoliosis, using BoNT/A. The disclosure of
Borodic is incorporated in its entirety herein by reference. In one
embodiment, using substantially similar methods as disclosed by Borodic, a
modified neurotoxin is administered to a mammal, preferably a human, to
treat spinal curvature. In a preferred embodiment, a modified neurotoxin
comprising BoNT/E fused with a leucine-based motif is administered. Even
more preferably, a modified neurotoxin comprising BoNT/E with a leucine-based
motif fused to the carboxyl terminal of its light chain is administered to
the mammal, preferably a human, to treat spinal curvature. The modified
neurotoxin may be administered to treat other neuromuscular disorders using
well known techniques that are commonly performed with BoNT/A.
Autonomic nervous system disorders may also be treated with a modified
neurotoxin. For example, glandular malfunctioning is an autonomic nervous
system disorder. Glandular malfunctioning includes excessive sweating and
excessive salivation. Respiratory malfunctioning is another example of an
autonomic nervous system disorder. Respiratory malfunctioning includes
chronic obstructive pulmonary disease and asthma. Sanders et al. discloses
methods for treating the autonomic nervous system, such as excessive
sweating, excessive salivation, asthma, etc., using naturally existing
botulinum toxins. The disclosure of Sander et al. is incorporated in its
entirety by reference herein. In one embodiment, substantially similar
methods to that of Sanders et al. may be employed, but using a modified
neurotoxin, to treat autonomic nervous system disorders such as the ones
discussed above. For example, a modified neurotoxin may be locally applied
to the nasal cavity of the mammal in an amount sufficient to degenerate
cholinergic neurons of the autonomic nervous system that control the mucous
secretion in the nasal cavity.
Pain that may be treated by a modified neurotoxin include pain caused by
muscle tension, or spasm, or pain that is not associated with muscle spasm.
For example, Binder in U.S. Pat. No. 5,714,468 discloses that headache
caused by vascular disturbances, muscular tension, neuralgia and neuropathy
may be treated with a naturally occurring botulinum toxin, for example BoNT/A.
The disclosures of Binder is incorporated in its entirety herein by
reference. In one embodiment, substantially similar methods to that of
Binder may be employed, but using a modified neurotoxin, to treat headache,
especially the ones caused by vascular disturbances, muscular tension,
neuralgia and neuropathy. Pain caused by muscle spasm may also be treated by
an administration of a modified neurotoxin. For example, a BoNT/E fused with
a leucine-based motif, preferably at the carboxyl terminal of the BoNT/E
light chain, may be administered intramuscularly at the pain/spasm location
to alleviate pain.
Furthermore, a modified neurotoxin may be administered to a mammal to treat
pain that is not associated with a muscular disorder, such as spasm. In one
broad embodiment, methods of the present invention to treat non-spasm
related pain include central administration or peripheral administration of
the modified neurotoxin.
For example, Foster et al. in U.S. Pat. No. 5,989,545 discloses that a
botulinum toxin conjugated with a targeting moiety may be administered
centrally (intrathecally) to alleviate pain. The disclosures of Foster et
al. is incorporated in its entirety by reference herein. In one embodiment,
substantially similar methods to that of Foster et al. may be employed, but
using the modified neurotoxin according to this invention, to treat pain.
The pain to be treated may be an acute pain, or preferably, chronic pain.
An acute or chronic pain that is not associated with a muscle spasm may also
be alleviated with a local, peripheral administration of the modified
neurotoxin to an actual or a perceived pain location on the mammal. In one
embodiment, the modified neurotoxin is administered subcutaneously at or
near the location of pain, for example at or near a cut. In another
embodiment, the modified neurotoxin is administered intramuscularly at or
near the location of pain, for example at or near a bruise location on the
mammal. In another embodiment, the modified neurotoxin is injected directly
into a joint of a mammal, for treating or alleviating pain cause arthritis
conditions. Also, frequent repeated injections or infusion of the modified
neurotoxin to a peripheral pain location is within the scope of the present
invention. However, given the long lasting therapeutic effects of the
present invention, frequent injections or infusion of the neurotoxin may not
be necessary. For example, practice of the present invention can provide an
analgesic effect, per injection, for 2 months or longer, for example 27
months, in humans.
Without wishing to limit the invention to any mechanism or theory of
operation, it is believed that when the modified neurotoxin is administered
locally to a peripheral location, it inhibits the release of neuro-substances,
for example substance P, from the peripheral primary sensory terminal. Since
the release of substance P by the peripheral primary sensory terminal may
cause or at least amplify pain transmission process, inhibition of its
release at the peripheral primary sensory terminal will dampen the
transmission of pain signals from reaching the brain.
In addition to having pharmacologic actions at the peripheral location, the
modified neurotoxin of the present invention may also have inhibitory
effects in the central nervous system. Presumably the retrograde transport
is via the primary afferent. This hypothesis is supported by our
experimental data which shows that BoNT/A is retrograde transported to the
dorsal horn when the neurotoxin is injected peripherally. Moreover, work by
Weigand et al, Nauny-Schmiedeberg's Arch. Pharmacol. 1976; 292, 161-165, and
Habermann, Nauny-Schmiedeberg's Arch. Pharmacol. 1974; 281, 47-56, showed
that botulinum toxin is able to ascend to the spinal area by retrograde
transport. As such, a modified neurotoxin, for example BoNt/A with one or
more amino acids deleted from the leucine-based motif, injected at a
peripheral location, for example intramuscularly, may be retrograde
transported from the peripheral primary sensory terminal to the central
primary sensory terminal.
The amount of the modified neurotoxin administered can vary widely according
to the particular disorder being treated, its severity and other various
patient variables including size, weight, age, and responsiveness to
therapy. Generally, the dose of modified neurotoxin to be administered will
vary with the age, presenting condition and weight of the mammal, preferably
a human, to be treated. The potency of the modified neurotoxin will also be
Assuming a potency which is substantially equivalent to LD.sub.50=2,730 U in
a human patient and an average person is 75 kg, a lethal dose would be about
36 U/kg of a modified neurotoxin. Therefore, when a modified neurotoxin with
such an LD.sub.50 is administered, it would be appropriate to administer
less than 36 U/kg of the modified neurotoxin into human subjects.
Preferably, about 0.01 U/kg to 30 U/kg of the modified neurotoxin is
administered. More preferably, about 1 U/kg to about 15 U/kg of the modified
neurotoxin is administered. Even more preferably, about 5 U/kg to about 10
U/kg modified neurotoxin is administered. Generally, the modified neurotoxin
will be administered as a composition at a dosage that is proportionally
equivalent to about 2.5 cc/100 U. Those of ordinary skill in the art will
know, or can readily ascertain, how to adjust these dosages for neurotoxin
of greater or lesser potency.
Although examples of routes of administration and dosages are provided, the
appropriate route of administration and dosage are generally determined on a
case by case basis by the attending physician. Such determinations are
routine to one of ordinary skill in the art (see for example, Harrison's
Principles of Internal Medicine (1998), edited by Anthony Fauci et al.,
14.sup.th edition, published by McGraw Hill). For example, the route and
dosage for administration of a modified neurotoxin according to the present
disclosed invention can be selected based upon criteria such as the
solubility characteristics of the modified neurotoxin chosen as well as the
types of disorder being treated.
The modified neurotoxin may be produced by chemically linking the leucine-based
motif to a neurotoxin using conventional chemical methods well known in the
art. The neurotoxin may be obtained from a harvesting neurotoxins. For
example, BoNt/E can be obtained by establishing and growing cultures of
Clostridium botulinum in a fermenter and then harvesting and purifying the
fermented mixture in accordance with known procedures. All the botulinum
toxin serotypes are initially synthesized as inactive single chain proteins
which must be cleaved or nicked by proteases to become neuroactive. The
bacterial strains that make botulinum toxin serotypes A and G possess
endogenous proteases and serotypes A and G can therefore be recovered from
bacterial cultures in predominantly their active form. In contrast,
botulinum toxin serotypes C.sub.1, D and E are synthesized by nonproteolytic
strains and are therefore typically unactivated when recovered from culture.
Serotypes B and F are produced by both proteolytic and nonproteolytic
strains and therefore can be recovered in either the active or inactive
form. However, even the proteolytic strains that produce, for example, the
BoNt/B serotype only cleave a portion of the toxin produced. The exact
proportion of nicked to unnicked molecules depends on the length of
incubation and the temperature of the culture. Therefore, a certain
percentage of any preparation of, for example, the BoNt/B toxin is likely to
be inactive, possibly accounting for the known significantly lower potency
of BoNt/B as compared to BoNt/A. The presence of inactive botulinum toxin
molecules in a clinical preparation will contribute to the overall protein
load of the preparation, which has been linked to increased antigenicity,
without contributing to its clinical efficacy. Additionally, it is known
that BoNt/B has, upon intramuscular injection, a shorter duration of
activity and is also less potent than BoNt/A at the same dose level.
The modified neurotoxin may also be produced by recombinant techniques.
Recombinant techniques are preferable for producing a neurotoxin having
amino acid sequence regions from different Clostridial species or having
modified amino acid sequence regions. Also, the recombinant technique is
preferable in producing BoNT/A with the leucine-based motif being modified
by deletion. The technique includes steps of obtaining genetic materials
from natural sources, or synthetic sources, which have codes for a neuronal
binding moiety, an amino acid sequence effective to translocate the
neurotoxin or a part thereof, and an amino acid sequence having therapeutic
activity when released into a cytoplasm of a target cell, preferably a
neuron. In a preferred embodiment, the genetic materials have codes for the
biological persistence enhancing component, preferably the leucine-based
motif, the H.sub.C, the H.sub.N and the L chain of the Clostridial
neurotoxins and fragments thereof. The genetic constructs are incorporated
into host cells for amplification by first fusing the genetic constructs
with a cloning vectors, such as phages or plasmids. Then the cloning vectors
are inserted into hosts, preferably E. coli's. Following the expressions of
the recombinant genes in host cells, the resultant proteins can be isolated
using conventional techniques.
There are many advantages to producing these modified neurotoxins
recombinantly. For example, to form a modified neurotoxin, a modifying
fragment must be attached or inserted into a neurotoxin. The production of
neurotoxin from anaerobic Clostridium cultures is a cumbersome and
time-consuming process including a multi-step purification protocol
involving several protein precipitation steps and either prolonged and
repeated crystallization of the toxin or several stages of column
chromatography. Significantly, the high toxicity of the product dictates
that the procedure must be performed under strict containment (BL-3). During
the fermentation process, the folded single-chain neurotoxins are activated
by endogenous clostridial proteases through a process termed nicking to
create a dichain. Sometimes, the process of nicking involves the removal of
approximately 10 amino acid residues from the single-chain to create the
dichain form in which the two chains remain covalently linked through the
intrachain disulfide bond.
The nicked neurotoxin is much more active than the unnicked form. The amount
and precise location of nicking varies with the serotypes of the bacteria
producing the toxin. The differences in single-chain neurotoxin activation
and, hence, the yield of nicked toxin, are due to variations in the serotype
and amounts of proteolytic activity produced by a given strain. For example,
greater than 99% of Clostridial botulinum serotype A single-chain neurotoxin
is activated by the Hall A Clostridial botulinum strain, whereas serotype B
and E strains produce toxins with lower amounts of activation (0 to 75%
depending upon the fermentation time). Thus, the high toxicity of the mature
neurotoxin plays a major part in the commercial manufacture of neurotoxins
as therapeutic agents.
The degree of activation of engineered clostridial toxins is, therefore, an
important consideration for manufacture of these materials. It would be a
major advantage if neurotoxins such as botulinum toxin and tetanus toxin
could be expressed, recombinantly, in high yield in rapidly-growing bacteria
(such as heterologous E. coli cells) as relatively non-toxic single-chains
(or single chains having reduced toxic activity) which are safe, easy to
isolate and simple to convert to the fully-active form.
With safety being a prime concern, previous work has concentrated on the
expression in E. coli and purification of individual H and L chains of
tetanus and botulinum toxins; these isolated chains are, by themselves,
non-toxic; see Li et al., Biochemistry 33:7014-7020 (1994); Zhou et al.,
Biochemistry 34:15175-15181 (1995), hereby incorporated by reference herein.
Following the separate production of these peptide chains and under strictly
controlled conditions the H and L chains can be combined by oxidative
disulphide linkage to form the neuroparalytic di-chains.
Claim 1 of 2 Claims
1. A modified botulinum neurotoxin type E
having increased biological half-life, wherein the modification comprises
the addition of the leucine-based motif of SEQ ID NO: 2, and wherein the
added leucine-based motif increases biological half-life of the modified
botulinum toxin type E relative to an identical botulinum toxin type E
without the added leucine-based motif.
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