STRUCTURAL STUDIES ON PROTEINS INVOLVED IN VESICLE TRANSPORT AND FUSION
Louise Kraft, Gunter Schneider and Ylva Lindqvist
Molecular Structural Biology, Department of
Medical Biochemistry and Biophysics, Karolinska Institutet, 171
77 Stockholm, Sweden
Release of chemical messengers from vesicles is the result of a highly ordered process of membrane trafficking [1]. The targeting of a vesicle to the appropriate acceptor membrane is proposed to occur through the formation of a 7S complex, composed of two vesicle proteins, VAMP or synaptobrevin and synaptotagmin, along with two target membrane proteins, SNAP-25 and syntaxin [2].
The steps following the formation of the 7S particle that lead to membrane fusion is less understood. One hypothesis is that energy of ATP hydrolysis drives a rearrangement of the VAMP and syntaxin proteins, thus promoting fusion of the lipid bilayers. It is likely that several additional intermediates are encountered prior to membrane fusion. The secretion is triggered by Ca2+ [3].
The aim of the research is to express, purify and solve the three dimensional structure of proteins involved in these processes. Crystallization experiments have been set up for syntaxin and SNAP-25. From one of these proteins, small crystals have been obtained. Amino acid sequencing revealed that the crystals are from a truncated form of the protein, probably due to proteolytic degradation. A new construct has been set up for crystallization experiments.