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Soluble N-ethylmaleimide-sensitive factor (NSF) Attachment Protein family Members of the soluble NSF attachment protein (SNAP) family are involved in intracellular membrane trafficking, including vesicular transport between the endoplasmic reticulum and Golgi apparatus. Higher eukaryotes contain three isoforms of SNAPs: alpha, beta, and gamma. Alpha-SNAP is universally present in eukaryotes and acts as an adaptor protein between SNARE (integral membrane SNAP receptor) and NSF for recruitment to the 20S complex. Beta-SNAP is brain-specific and shares high sequence identity (about 85%) with alpha-SNAP. Gamma-SNAP is weakly related (about 20-25% identity) to the two other isoforms, and is ubiquitous. It may help regulate the activity of the 20S complex. The X-ray structures of vertebrate gamma-SNAP and yeast Sec17, a SNAP family member, show similar all-helical structures consisting of an N-terminal extended twisted sheet of four Tetratricopeptide repeat (TPR)-like helical hairpins and a C-terminal helical bundle.
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