SYNAPSIN-I IS STRUCTURALLY SIMILAR TO ATP-UTILIZING ENZYMES

Synapsins are abundant synaptic vesicle proteins with an essential reg ulatory function in the nerve terminal. We determined the crystal stru cture of a fragment (synC) consisting of residues 110-420 of bovine sy napsin I; synC coincides with the large middle domain (C-domain), the most conserved domain of synapsins. SynC molecules are folded into com pact domains and form closely associated dimers. SynC monomers are str ikingly similar in structure to a family of ATP-utilizing enzymes, whi ch includes glutathione synthetase and D-alanine:D-alanine ligase. Syn C binds ATP in a Ca2+-dependent manner. The crystal structure of synC in complex with ATP gamma S and Ca2+ explains the preference of synC f or Ca2+ over Mg2+. Our results suggest that synapsins may also be ATP- utilizing enzymes.