Crystallization and preliminary X-ray analysis of squid neuronal Sec1

Sec1 protein family members are involved in the regulation of all intracell ular SNARE-mediated (SNARE = soluble N-ethylmaleimide-sensitive fusion prot ein attachment protein receptor) vesicle-fusion processes in a step precedi ng membrane fusion and have been shown to interact with t-SNAREs. To better understand the structural basis and the role of Sec1 in the regulation of the SNARE-complex formation, neuronal Sec1 from the squid Loligo pealei has been expressed and crystallized; this invertebrate protein shows a high se quence homology to the human neuronal Sec1, Munc18a. Here, the production o f diffraction-quality native crystals, which belong to space group P3(1)21 and diffract to 3.3 Angstrom resolution, is described. In addition, selenom ethionyl n-Sec1 crystals in space groups P3(1)21 and P2(1) have been genera ted. Preliminary analysis of the monoclinic space group indicates that thes e crystals diffract to a resolution higher than 2.5 Angstrom.