Crystallization and preliminary X-ray analysis of squid neuronal Sec1

Sec1 protein family members are involved in the regulation of all intracellular SNARE-mediated (SNARE = soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) vesicle-fusion processes in a step preceding 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 sequence homology to the human neuronal Sec1, Munc18a. Here, the production of diffraction-quality native crystals, which belong to space group P3(1)21 and diffract to 3.3 A resolution, is described. In addition, selenomethionyl n-Sec1 crystals in space groups P3(1)21 and P2(1) have been generated. Preliminary analysis of the monoclinic space group indicates that these crystals diffract to a resolution higher than 2.5 A.