Biomedical subjects

M A Poirier

Publications and source records attributed to M A Poirier.

6 recordsLinked to original sources

PubMed2001

The neuronal t-SNARE complex is a parallel four-helix bundle.

Assembly of the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complex is an essential step for neurotransmitter release in synapses. The presynaptic plasma membrane associated proteins (t-SNAREs), SNAP-25 (synaptosome-associated protein of 25,000 Da) and syntaxin 1A may form an intermediate complex that later binds to vesicle-associated membrane protein 2 (VAMP2). Using spin labeling electron paramagnetic resonance (EPR), we found that the two t-SNARE proteins assemble into a parallel four-helix bundle that consists of two identical syntaxin 1A components and the N-terminal and C-terminal domains of SNAP-25. Although the structure is generally similar to that of the final SNARE complex, the middle region of the helical bundle appears more flexible in the t-SNARE complex. Such flexibility might facilitate interactions between VAMP2 and the t-SNARE complex.

Electron Spin Resonance Spectroscopy↗

PubMed1998

Protease resistance of syntaxin.SNAP-25.VAMP complexes. Implications for assembly and structure.

A stable ternary complex formed with vesicle-associated membrane protein 2 (VAMP2) and plasma membrane proteins syntaxin 1A and synaptosome-associated protein of 25 kDa (SNAP-25) is proposed to function in synaptic vesicle exocytosis. To analyze the structural characteristics of this synaptic protein complex, recombinant binary (syntaxin 1A.SNAP-25), recombinant ternary, and native ternary complexes were subjected to limited trypsin proteolysis. The protected fragments, defined by amino-terminal sequencing and mass spectrometry, included a carboxyl-terminal region of syntaxin 1A, the cytoplasmic domain of VAMP2, and amino- and carboxyl-terminal regions of SNAP-25. Furthermore, separate amino- and carboxyl-terminal fragments of SNAP-25, when combined with VAMP2 and syntaxin 1A, were sufficient for stable complex assembly. Analysis of ternary complexes formed with full-length proteins revealed that the carboxyl-terminal transmembrane anchors of both syntaxin 1A and VAMP2 were protected from trypsin digestion. Moreover, the stability of ternary complexes was increased by inclusion of these transmembrane domains. These results suggest that the transmembrane domains of VAMP2 and syntaxin 1A contribute to complex assembly and stability and that amino- and carboxyl-terminal regions of SNAP-25 may function as independent domains.

Animals↗

PubMed1998

The synaptic SNARE complex is a parallel four-stranded helical bundle.

The heterotrimeric synaptic soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, consisting of the synaptic vesicle-associated membrane protein 2 (VAMP2) and presynaptic plasma membrane proteins SNAP-25 (synaptosome-associated protein of 25,000 Mr) and syntaxin 1A, is a critical component of the exocytotic machinery. We have used spin labeling electron paramagnetic resonance spectroscopy to investigate the structural organization of this complex, particularly the two predicted helical domains contributed by SNAP-25. Our results indicate that the N- and C-terminal domains of SNAP-25 are parallel to each other and to the C-terminal domain of syntaxin 1A. Based on these findings, we propose a parallel four-stranded coiled coil model for the structure of the synaptic SNARE complex.

Animals↗

PubMed1980

Identification of degradation products in a phenylbutazone tablet formulation.

Two previously reported but unidentified phenylburazone degradation products were isolated from a tablet that was stored at 60 degrees for 203 days. The compounds, alpha-(N-phenylcarbamoyl)-N-caproylhydrazobenzene and alpha-hydroxy-alpha-(N-phenylcarbamoyl)-N-caproylhydrazobenzene, were isolated by chromatography, identified by mass and NMR spectrometry, and synthesized by the reaction of aniline with phenylbutazone or its hydroxy analog, respectively.

Chemical Phenomena↗

PubMed1980

Impurities in drugs V: Meprobamate.

One lot of meprobamate raw material and 28 lots of tablets were examined for impurities by TLC. All lots contained di-(2-methyl-2-propyl-3-carbamoyloxypropyl) carbonate (V) at levels that ranged between 0.1 and 1.0% of the total drug content. Nine lots also contained low levels of a second impurity (approximately 0.1%), and one of these lots contained a third impurity (approximately 0.1%), neither of which was identified. Estimates of the unidentified impurities were based on the assumption of a TLC response with furfural-hydrochloric acid spray equivalent to that of meprobamate. Compound V was identified by mass spectrometry and PMR and IR spectroscopy and by comparison of the TLC Rf value to that of a synthesized sample of V.

Chromatography, Thin Layer↗

PubMed1979

Impurities in drugs III: Trihexyphenidyl.

Two lots of trihexyphenidyl hydrochloride raw material, one lot of elixir, and 10 lots of tablets were examined for impurities by TLC. Impurities found were 1-phenyl-2-propenone, 3-piperidinopropiophenone, and 3-aminopropiophenone. Not all impurities were present in all lots, and none exceeded 1.9% of the label drug claim. Impurities were identified by mass spectrometry and by comparison of TLC Rf values and GLC retention times to those of synthesized specimens of the impurities.

Chromatography, Thin Layer↗