ABSTRACT
Complexins are evolutionarily conserved proteins that specifically bind to soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes and thus may regulate SNARE function. Using purified proteins, we have performed a detailed analysis of the structure of complexin and of its interaction with SNARE proteins. NMR spectroscopy revealed that isolated complexins have no tertiary structure but contain an unusual alpha-helical middle domain of approximately 58 amino acids that overlaps with the most highly conserved region of the molecules. Complexins form a stable stoichiometric complex with the central domain of the ternary SNARE complex, whereas no binding was observed to monomeric SNAREs. Using a combination of limited proteolysis, deletion mutagenesis, and NMR spectroscopy, we found that the helical middle region of complexin is responsible for binding to the SNARE complex. Binding was highly sensitive to substitution of syntaxin 1 or synaptobrevin 2 with other SNARE homologs but less sensitive to substitution of SNAP-25. In addition, a stretch of 12 amino acids in the middle of the SNARE motif of syntaxin 1A was able to confer binding activity to the non-binding relative syntaxin 4. Furthermore, disassembly of ternary complexes is not affected by complexins. We conclude that complexins are specific ligands of the neuronal core complex that bind with a central alpha-helical domain, probably to the middle of the surface groove formed by synaptobrevin and syntaxin. Complexins may regulate the function of ternary complexes and control membrane fusion through this interaction.
Subject(s)
Membrane Proteins/metabolism , Nerve Tissue Proteins/metabolism , Neurons/chemistry , Vesicular Transport Proteins , Adaptor Proteins, Vesicular Transport , Amino Acid Sequence , Animals , Antigens, Surface/metabolism , Binding Sites , Escherichia coli/metabolism , Magnetic Resonance Spectroscopy , Membrane Proteins/chemistry , Molecular Sequence Data , Mutagenesis , Nerve Tissue Proteins/chemistry , Nerve Tissue Proteins/genetics , Plasmids , Protein Binding , Protein Structure, Secondary , Protein Structure, Tertiary , Proteolipids/metabolism , R-SNARE Proteins , Rats , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/metabolism , SNARE Proteins , Sequence Homology, Amino Acid , Syntaxin 1ABSTRACT
Recently, we demonstrated that an array biosensor could be used with cocktails of fluorescent antibodies to perform three assays simultaneously on a single substrate, and that multiple samples could be analyzed in parallel. We extend this technology to demonstrate the simultaneous analysis of six samples for six different hazardous analytes, including both bacteria and protein toxins. The level of antibody cross-reactivity is explored, revealing a possible common epitope in two of the toxins. A panel of environmental interferents was added to the samples; these interferents neither prevented the detection of the analytes nor caused false-positive responses.
