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Biomedical subjects

J B Cohen

Publications and source records attributed to J B Cohen.

At least 37 records · Page 2Linked to original sources
PubMed2000

HSV vector cytotoxicity is inversely correlated with effective TK/GCV suicide gene therapy of rat gliosarcoma.

Herpes simplex virus (HSV)-mediated delivery of the HSV thymidine kinase (tk) gene to tumor cells in combination with ganciclovir (GCV) administration may provide an effective suicide gene therapy for destruction of malignant glioblastomas. However, because HSV is a highly cytotoxic agent, gene expression from the virus is short-lived which may limit the effectiveness of HSVtk/GCV therapy. Using different replication-defective HSVtk gene vectors, we compared HSV vector backgrounds for their cytotoxic activity on infection of 9L gliosarcoma cells in culture and brain tumors in rats and evaluated the impact of vector toxicity on the effectiveness of tk/GCV-mediated suicide gene therapy. As reported previously for other cell lines, a vector deleted for both copies of the immediate-early (IE) gene ICP4 (SOZ.1) was highly toxic for 9L cells in culture while a vector deleted in addition for the ICP22 and ICP27 IE genes (T.1) reduced or arrested 9L cell proliferation with more limited cell killing. Nevertheless, both vectors supported widespread killing of uninfected cells in the presence of GCV following low multiplicity infections, indicating that vector cytotoxicity did not preempt the production of vector-encoded TK enzyme necessary for the killing of uninfected cells by the HSV-tk/GCV bystander effect. Although an SOZ.1-related vector (SHZ.2) caused tumor cell necrosis in vivo, injection of SHZ.2 at multiple coordinates thoughout the tumor followed by GCV administration failed to prolong markedly the survival of tumor-bearing rats. In contrast, a single injection of T.1 produced a life-extending response to GCV. These results indicate that vector cytotoxicity can limit the efficacy of HSV-tk/GCV treatment in vivo, which may be due to premature termination of tk gene expression with attendant abortion of the bystander effect.

Animals↗
PubMed2000

Penile Kaposi's sarcoma preceded by chronic penile lymphoedema.

Kaposi's sarcoma localized to the penis with striking lymphoedema is extraordinary. We report a middle-aged Haitian man who was human herpesvirus-8 seropositive, without evidence of immunosuppression or human immunodeficiency virus infection. He was first seen with Kaposi's sarcoma of 6 months duration localized to his penis, preceded by a 3-year history of chronic penile lymphoedema. His tumour regressed completely after radiotherapy. We propose that chronic lymphoedema in this patient predisposed to the development of Kaposi's sarcoma.

Humans↗
PubMed2000

Pseudotyping of glycoprotein D-deficient herpes simplex virus type 1 with vesicular stomatitis virus glycoprotein G enables mutant virus attachment and entry.

The use of herpes simplex virus (HSV) vectors for in vivo gene therapy will require the targeting of vector infection to specific cell types in certain in vivo applications. Because HSV glycoprotein D (gD) imparts a broad host range for viral infection through recognition of ubiquitous host cell receptors, vector targeting will require the manipulation of gD to provide new cell recognition specificities in a manner designed to preserve gD's essential role in virus entry. In this study, we have determined whether an entry-incompetent HSV mutant with deletions of all Us glycoproteins, including gD, can be complemented by a foreign attachment/entry protein with a different receptor-binding specificity, the vesicular stomatitis virus glycoprotein G (VSV-G). The results showed that transiently expressed VSV-G was incorporated into gD-deficient HSV envelopes and that the resulting pseudotyped virus formed plaques on gD-expressing VD60 cells, albeit at a 50-fold-reduced level compared to that of wild-type gD. This reduction may be related to differences in the entry pathways used by VSV and HSV or to the observed lower rate of incorporation of VSV-G into virus envelopes than that of gD. The rate of VSV-G incorporation was greatly improved by using recombinant molecules in which the transmembrane domain of HSV glycoprotein B or D was substituted for that of VSV-G, but these recombinant molecules failed to promote virus entry. These results show that foreign glycoproteins can be incorporated into the HSV envelope during replication and that gD can be dispensed with on the condition that a suitable attachment/entry function is provided.

Gene Targeting↗
PubMed1999

Synthesis and properties of 3-(2-hydroxyethyl)-3-n-pentyldiazirine, a photoactivable general anesthetic.

To overcome the difficulties of locating the molecular sites of general anesthetic action, we synthesized a novel photoactivable general anesthetic, 3-(2-hydroxyethyl)-3-n-pentyldiazirine (3-diazirinyloctanol), which anesthetized tadpoles with an ED(50) of 160 microM. Subanesthetic concentrations of 3-diazirinyloctanol enhanced GABA-induced currents in GABA(A) receptors, an effect that has been implicated in general anesthetic action. It also enhanced [(3)H]muscimol binding to this receptor. In muscle nicotinic acetylcholine receptors (nAcChoR), it inhibited the response to acetylcholine with an IC(50) of 33 microM. 3-Diazirinyloctanol's pharmacological actions were comparable to those of octanol. 3-(2-Hydroxyethyl)-3-[4,5-(3)H(2)]-n-pentyldiazirine photoincorporated into Torpedo nAcChoR-rich membranes mainly in the alpha subunit with 70% being in a proteolytic fragment containing the M4 transmembrane segment. Agonist enhanced the photolabeling 10-fold in a fragment containing the M1, M2, and M3 transmembrane segments. Thus, 3-diazirinyloctanol is a novel general anesthetic that acts on, and can be photoincorporated into, postsynaptic receptors.

Allosteric Regulation↗
PubMed1999

Structure of the agonist-binding sites of the Torpedo nicotinic acetylcholine receptor: affinity-labeling and mutational analyses identify gamma Tyr-111/delta Arg-113 as antagonist affinity determinants.

Photoaffinity labeling of the Torpedo nicotinic acetylcholine receptor (nAChR) with [3H]d-tubocurarine (dTC) has identified a residue within the gamma-subunit which, along with the analogous residue in delta-subunit, confers selectivity in binding affinities between the two agonist sites for dTC and alpha-conotoxin (alpha Ctx) MI. nAChR gamma-subunit, isolated from nAChR-rich membranes photolabeled with [3H]dTC, was digested with Staphylococcus aureus V8 protease, and a 3H-labeled fragment was purified by reversed-phase high-performance liquid chromatography. Amino-terminal sequence analysis of this fragment identified 3H incorporation in gamma Tyr-111 and gamma Tyr-117 at about 5% and 1% of the efficiency of [3H]dTC photoincorporation at gamma Trp-55, the primary site of [3H]dTC photoincorporation within gamma-subunit [Chiara, D. C., and Cohen, J. B. (1997) J. Biol. Chem 272, 32940-32950]. The Torpedo nAChR delta-subunit residue corresponding to gamma Tyr-111 (delta Arg-113) contains a positive charge which could confer the lower binding affinity seen for some competitive antagonists at the alpha-delta agonist site. To test this hypothesis, we examined by voltage-clamp analysis and/or by [125I]alpha-bungarotoxin competition binding assays the interactions of acetylcholine (ACh), dTC, and alpha Ctx MI with nAChRs containing gamma Y111R or delta R113Y mutant subunits expressed in Xenopus oocytes. While these mutations affected neither ACh equilibrium binding affinity nor the concentration dependence of channel activation, the gamma Y111R mutation decreased by 10-fold dTC affinity and inhibition potency. Additionally, each mutation conferred a 1000-fold change in the equilibrium binding of alpha Ctx MI, with delta R113Y enhancing and gamma Y111R weakening affinity. Comparison of these results with previous results for mouse nAChR reveals that, while the same regions of gamma- (or delta-) subunit primary structure contribute to the agonist-binding sites, the particular amino acids that serve as antagonist affinity determinants are species-dependent.

Amino Acid Sequence↗
PubMed1999

The steroid promegestone is a noncompetitive antagonist of the Torpedo nicotinic acetylcholine receptor that interacts with the lipid-protein interface.

17,21-Dimethyl-19-nor-pregn-4,9-diene-3,20-dione (promegestone) was used to characterize the mechanism of inhibition of nicotinic acetylcholine (ACh) receptors (AChR) by progestin steroids. Promegestone reversibly inhibited ACh-induced currents of Torpedo AChRs expressed in Xenopus oocytes. Between 1-30 microM promegestone produced a concentration-dependent enhancement of the equilibrium binding affinity of [3H]ACh to Torpedo AChR-rich membranes. For AChRs in the presence of agonist (desensitized state) promegestone was a more potent inhibitor of the binding of the noncompetitive antagonist [3H]phencyclidine (IC50 = 9 microM) than of [3H]histrionicotoxin (IC50 approximately 100 microM). To identify AChR domains in contact with the steroid, AChR-rich membranes equilibrated with [3H]promegestone were irradiated at 312 nm, and 3H-labeled amino acids were identified by amino-terminal sequencing of fragments isolated from subunit proteolytic digests. Within AChR alpha-subunit, 70% of 3H was covalently incorporated in a 10-kDa fragment beginning at Asn-339 and containing the M4 membrane spanning segment, and 30% was in a 20-kDa fragment beginning at Ser-173 and containing the M1-M3 segments. Fragments containing the M2 channel domains as well as the M4 segments were isolated from proteolytic digests of AChR subunits and subjected to amino-terminal sequence analysis. No evidence of [3H]promegestone incorporation was detected in any of the M2 segments. The amino acids in the M4 segments labeled by [3H]promegestone were among those previously shown to be in contact with the lipid bilayer (). These results indicate that the steroid promegestone is an AChR noncompetitive antagonist that may alter AChR function by interactions at the lipid-protein interface.

Acetylcholine↗
PubMed1999

Photoaffinity labeling the torpedo nicotinic acetylcholine receptor with [(3)H]tetracaine, a nondesensitizing noncompetitive antagonist.

Tetracaine (N,N-dimethylaminoethyl-4-butylaminobenzoate) and related N,N-dialkylaminoethyl substituted benzoic acid esters have been used to characterize the high-affinity binding site for aromatic amine noncompetitive antagonists in the Torpedo nicotinic acetylcholine receptor (nAChR). [(3)H]Tetracaine binds at equilibrium to a single site with a K(eq) value of 0.5 microM in the absence of agonist or presence of alpha-bungarotoxin and with a K(eq) value of 30 microM in the presence of agonist (i.e., for nAChR in the desensitized state). Preferential binding to nAChR in the absence of agonist is also seen for N,N-DEAE and N,N-diethylaminopropyl esters, both binding with 10-fold higher affinity in the absence of agonist than in the presence, and for the 4-ethoxybenzoic acid ester of N, N-diethylaminoethanol, but not for the 4-amino benzoate ester (procaine). Irradiation at 302 nm of nAChR-rich membranes equilibrated with [(3)H]tetracaine resulted in covalent incorporation with similar efficiency into nAChR alpha, beta, gamma, and delta subunits. The pharmacological specificity of nAChR subunit photolabeling as well as its dependence on [(3)H]tetracaine concentration establish that the observed photolabeling is at the high-affinity [(3)H]tetracaine-binding site. Within alpha subunit, >/=95% of specific photolabeling was contained within a 20-kilodalton proteolytic fragment beginning at Ser(173) that contains the M1 to M3 hydrophobic segments. With all four subunits contributing to [(3)H]tetracaine site, the site in the closed channel state of the nAChR is most likely within the central ion channel domain.

Animals↗
PubMed1999

Identification of amino acids of the torpedo nicotinic acetylcholine receptor contributing to the binding site for the noncompetitive antagonist [(3)H]tetracaine.

[(3)H]Tetracaine is a noncompetitive antagonist of the Torpedo nicotinic acetylcholine receptor (nAChR) that binds with high affinity in the absence of cholinergic agonist (K(eq) = 0.5 microM) and weakly (K(eq) = 30 microM) in the presence of agonist (i.e., to nAChR in the desensitized state). In the absence of agonist, irradiation at 302 nm of nAChR-rich membranes equilibrated with [(3)H]tetracaine results in specific photoincorporation of [(3)H]tetracaine into each nAChR subunit. In this report, we identify the amino acids of each nAChR subunit specifically photolabeled by [(3)H]tetracaine that contribute to the high-affinity binding site. Subunits isolated from nAChR-rich membranes photolabeled with [(3)H]tetracaine were subjected to enzymatic digestion, and peptides containing (3)H were purified by SDS-polyacrylamide gel electrophoresis followed by reversed phase HPLC. N-terminal sequence analysis of the isolated peptides demonstrated that [(3)H]tetracaine specifically labeled two sets of homologous hydrophobic residues (alphaLeu(251), betaLeu(257), gammaLeu(260), and deltaLeu(265); alphaVal(255) and deltaVal(269)) as well as alphaIle(247) and deltaAla(268) within the M2 hydrophobic segments of each subunit. The labeling of these residues establishes that the high-affinity [(3)H]tetracaine-binding site is located within the lumen of the closed ion channel and provides a definition of the surface of the M2 helices facing the channel lumen.

Amino Acids↗
PubMed1999

Genetic studies exposing the splicing events involved in herpes simplex virus type 1 latency-associated transcript production during lytic and latent infection.

Herpes simplex virus type 1 (HSV-1) establishes latency in sensory neurons, a state in which the viral lytic genes are silenced and only the latency locus is transcriptionally active, producing the 2. 0- and 1.5-kb latency-associated transcripts (LATs). Previous experimental evidence indicates that the LATs are stable introns, and it has been reported that LAT formation is abolished by debilitating substitution mutations in the predicted splice sites during lytic infection but not latency (J. L. Arthur et al., J. Gen. Virol. 79:107-116, 1998). We have independently studied a set of deletion mutations to explore the roles of the proposed splice sites during lytic and latent infection. HSV-1 mutant viruses missing the invariant intron-terminal 5'-G(T/C) or 3'-AG dinucleotides were analyzed for LAT formation during lytic infection in vitro, when only the 2-kb LAT is produced, and during latency in mouse trigeminal ganglia, where both LATs are expressed. Northern blot analysis of total RNAs from different productively infected cell lines showed that the lytic (2-kb) LAT was not expressed by the various splice site deletion mutants. In vivo studies using a mouse eye model of latency similarly showed that the latent (2- and 1. 5-kb) LATs were not expressed by the mutants. PCR analysis with primers flanking the LAT sequence revealed the expected splice junction for LAT excision in RNA from sensory neurons latently infected with wild-type but not mutant virus. Using a virus mutant deleted in the splicing signals flanking the 556-bp region of LAT whose absence distinguishes the 1.5- and 2-kb LATs, we observed selective elimination of 1.5-kb LAT expression in latency, supporting previous suggestions that the internal region is removed by splicing. Taken together, these results demonstrate that the 2-kb LAT is formed during both lytic and latent infection by splicing at the predicted splice sites and that an additional splicing event is involved in the latency-restricted production of the 1.5-kb LAT. We have also mapped the 3' end of the lytic 2-kb LAT and discuss our results in the context of previous models addressing the unusual stability of the LATs.

Animals↗
PubMed1999

Hereditary hypodontia and onychorrhexis of the fingernails and toenail koilonychia: Witkop's tooth-and nail syndrome.

The tooth-and-nail syndrome (Witkop's syndrome) is a rare autosomal dominant ectodermal dysplasia manifest by defects of the nail plates of the fingers and toes and hypodontia with normal hair and sweat gland function. We report a thirteen year-old girl who presented with marked longitudinal ridging of the nail plates of all ten fingers. The toenails were mildly ridged with koilonychia. Her mother's fingers were similarly affected to a lesser degree while her toenails appeared normal. Examination of the child's dentition revealed a hyperplastic frenulum and the absence of one of the usual four mandibular incisors. History provided by the mother described the maternal grandmother and maternal great aunt as having identical nail findings and the presence of only three lower incisors. Hair examination was normal in the mother and child, and no history or findings of sweat gland dysfunction was present. This report describes familial hypodontia, fingernail onychorrhexis, and toenail koilonychia consistent with Witkop's syndrome.

Adolescent↗
PubMed1998

Spatial structure of the M3 transmembrane segment of the nicotinic acetylcholine receptor alpha subunit.

The three-dimensional structure of a synthetic peptide corresponding to the putative transmembrane segment M3 (amino acid residues 277-301) of the alpha subunit of the nicotinic acetylcholine receptor from Torpedo californica has been studied by means of two-dimensional 1H-NMR spectroscopy in a chloroform/methanol (1:1) mixture containing 0.1 M LiClO4. Complete resonance assignment has been performed using double-quantum-filtered COSY (DQF-COSY), TOCSY and NOESY spectra. The spatial structure has been calculated using the Diana program on the basis of integrated intensities of NOESY spectra. HN-C(alpha)H and HC(alpha)-C(beta)H spin-spin coupling constants. Residues 279-297 of M3 form a right-handed helix (root mean square deviation is 0.032 nm for backbone atoms and 0.088 nm for all heavy atoms). The conformations of the 17 side chains have been unambiguously determined. The obtained structure is in accord with the photolabeling pattern of the membrane nicotinic acetylcholine receptor (nAChR) which suggests alpha-helical structure of M3 in the labeled portion [Blanton, M. P. & Cohen, J. B. (1994) Biochemistry 33, 2859-2872].

Amino Acid Sequence↗
PubMed1998

Probing the structure of the nicotinic acetylcholine receptor ion channel with the uncharged photoactivable compound -3H-diazofluorene.

The uncharged photoactivable probe 2-[3H]diazofluorene ([3H]DAF) was used to examine structural changes in the Torpedo californica nicotinic acetylcholine receptor (AChR) ion channel induced by agonists. Photoincorporation of [3H]DAF into the AChR consisted of the following two components: a nonspecific component consistent with incorporation into residues situated at the lipid-protein interface, and a specific component, inhibitable by noncompetitive antagonists and localized to the M2 hydrophobic segments of AChR subunits. The nonspecific [3H]DAF incorporation was characterized in the M4 segment of each AChR subunit. The observed distribution and periodicity of labeled residues reinforce the conclusion that the M4 segments are organized as transmembrane alpha-helices with a common "face" of each helix in contact with lipid. Within the M2 segments, in the absence of agonist [3H]DAF specifically labeled homologous residues betaVal-261 and deltaVal-269, with incorporation into deltaVal-269 at a 5-fold greater efficiency than into betaVal-261. This observation, coupled with the lack of detectable incorporation into alpha-M2 including the homologous alphaVal-255, indicates that within the resting channel [3H]DAF is bound with its photoreactive diazo group oriented toward deltaVal-269. In the presence of agonist, there is an approximately 90% reduction in the labeling of betaVal-261 and deltaVal-269 accompanied by specific incorporation into residues (betaLeu-257, betaAla-258, deltaSer-262, and deltaLeu-265) situated 1 or 2 turns of an alpha-helix closer to the cytoplasmic end of the M2 segments. The results provide a further characterization of agonist-induced rearrangements of the M2 (ion channel) domain of the AChR.

Affinity Labels↗
PubMed1998

Mechanism of nicotinic acetylcholine receptor cluster formation by rapsyn.

Rapsyn, a peripheral membrane protein of skeletal muscle, clusters nicotinic acetylcholine receptors (nAChRs) at high density in the postsynaptic membrane. The mechanism of nAChR clustering by rapsyn was analyzed by expressing nAChRs in HEK293T cells with various fragments of mouse rapsyn fused to green fluorescent protein. Membrane targeting of rapsyn is conferred solely by its acylated N terminus, as the myristoylated N-terminal 15 amino acids of rapsyn are sufficient to target green fluorescent protein to the plasma membrane. However, neither N-terminal myristoylation nor the conserved N-terminal amino acid sequence is essential. Membrane targeting, self-association, and nAChR clustering are preserved when the first 10 amino acids of rapsyn were replaced by those of src, which also contains a consensus sequence for N-myristoylation, or by those of GAP43, which contains a palmitoylation sequence. Rapsyn1-90, containing two tetratrichopeptide repeats is sufficient for self-association. Rapsyn1-360, lacking the cysteine rich domain, clusters nAChRs, while rapsyn1-287, containing seven tetratrichopeptide repeats, does not cluster nAChRs. We identified rapsyn298-331 as a potential coiled-coil domain, and established that mutations disrupting coiled-coil propensity prevent nAChR clustering. Thus the structural domains of rapsyn necessary for membrane targeting, self-association, and nAChR clustering are distinct, with nAChR-rapsyn interaction mediated by a previously unrecognized coiled-coil motif.

Amino Acid Substitution↗
PubMed1998

Identification of tryptophan 55 as the primary site of [3H]nicotine photoincorporation in the gamma-subunit of the Torpedo nicotinic acetylcholine receptor.

[3H]nicotine has been used as a photoaffinity agonist to identify amino acids within the Torpedo nicotinic acetylcholine receptor (nAChR) gamma-subunit that contributes to the structure of the agonist binding site. UV irradiation (254 nm) of nAChR-rich membranes equilibrated with [3H]nicotine results in covalent incorporation into alpha- and gamma-subunits that is inhibitable by agonists and competitive antagonists, but not by non-competitive antagonists (Middleton, R.E. and Cohen, J.B. (1991) Biochemistry 30, 6887-6897). To identify sites of specific incorporation, SDS-PAGE and reversed-phase HPLC were used to isolate proteolytic fragments of [3H]nicotine-labeled gamma-subunit. Amino-terminal sequence analysis identified gammaTrp-55 as the major site of [3H]nicotine photoincorporation in gamma-subunit. Thus gammaTrp-55 is the first amino acid within a non-alpha-subunit to be identified by affinity labeling in direct contact with a bound agonist.

Animals↗
PubMed1998

Development of herpes simplex virus replication-defective multigene vectors for combination gene therapy applications.

Some gene therapy applications will require simultaneous expression of multiple gene products to achieve a therapeutic effect. In this study we describe the generation and characterization of replication incompetent herpes simplex virus type 1 (HSV-1) vectors (HX86Z or HX86G) carrying distinct and independently regulated expression cassettes for five transgenes (hIL-2, hGM-CSF, hB7.1, HSV-tk and lacZ or hIFN gamma). The transgenes, representing 12 kb of DNA sequence, were recombined into separate loci of a single mutant virus vector deleted for 11.6 kb of vector sequences representing portions of nine viral genes, ICP4, ICP22, ICP27, ICP47, UL24, UL41, UL44, US10 and US11. Deletion of the immediate--early genes ICP4, ICP22 and ICP27 substantially reduced vector cytotoxicity, prevented early and late viral gene expression and left intact MHC class I antigen expression. Simultaneous expression of multiple transgenes was obtained for up to 7 days in primary human melanoma cells with peak expression at 2-3 days after infection. The transgenes were chosen for their potential to function synergistically in tumor destruction and vaccine gene therapy applications, but the method and vector employed could be applied to other multigene therapy strategies. This study demonstrates the potential for engineering large transgene capacity DNA viruses such as HSV-1 for expression of multiple transgenes.

Defective Viruses↗
PubMed1997

Identification of amino acids contributing to high and low affinity d-tubocurarine sites in the Torpedo nicotinic acetylcholine receptor.

d-Tubocurarine (dTC) is a potent competitive antagonist of the Torpedo nicotinic acetylcholine receptor (nAChR) that binds non-equivalently to the two agonist sites (Kd values of 30 nM and 8 microM). When nAChR-rich membranes equilibrated with [3H]dTC are irradiated with 254 nm UV light, [3H]dTC is covalently incorporated into the alpha-, gamma-, and delta-subunits in a concentration-dependent and agonist-inhibitable manner, consistent with the localization of the high and low affinity dTC binding sites at the alpha-gamma- and alpha-delta-subunit interfaces, respectively (Pedersen, S. E. and Cohen, J. B. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 2785-2789). We report on the amino acids within alpha-, gamma-, and delta-subunits that are the sites of specific photoincorporation of [3H]dTC. Subunits isolated from nAChR-rich membranes photolabeled with [3H]dTC were subjected to enzymatic digestion, and peptides containing 3H were isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and/or reversed-phase high performance liquid chromatography. Isolated peptides were then subjected to NH2-terminal sequence analysis to identify specifically labeled residues. Within the alpha-subunit, 95% of specific incorporation was contained within a 20-kDa proteolytic fragment beginning at Ser-173, with alphaTyr-190 the primary site of [3H]dTC photoincorporation and alphaCys-192 and alphaTyr-198 labeled at lower efficiency. Within gamma- and delta-subunits, specific labeling was contained within proteolytic fragments of 14 and 21 kDa, respectively, beginning at gammaAla-49 and deltaThr-51. gammaTrp-55 and deltaTrp-57 were identified as the sites of specific [3H]dTC photoincorporation. Sequence alignment studies reveal gammaTrp-55 and deltaTrp-57 to be homologous residues at whose position in receptor subunit primary structure a unique pattern of conservation exists in all nAChR (neuronal and muscle). Specifically, all subunits that associate with an alpha-subunit to form an agonist site contain a tryptophan homologous to gammaTrp-55/deltaTrp-57. This pattern of conservation may indicate a functional significance for tryptophan at that location in all nAChR agonist sites.

Amidohydrolases↗