title: Tetramerization and ATP binding by a protein comprising the A, B, and C domains of rat synapsin I.
abstract: Synapsins are multidomain proteins that are critical for regulating neurotransmitter release in vertebrates. In the present study, two crystal structures of the C domain of rat synapsin I (rSynI-C) in complex with Ca(2+) and ATP reveal that this protein can form a tetramer and that a flexible loop (the "multifunctional loop") contacts bound ATP. Further experiments were carried out on a protein comprising the A, B, and C domains of rat synapsin I (rSynI-ABC). An ATP-stabilized tetramer of rSynI-ABC is observed during velocity sedimentation and size-exclusion chromatographic experiments. These hydrodynamic results also indicate that the A and B domains exist in an extended conformation. Calorimetric measurements of ATP binding to wild-type and mutant rSynI-ABC demonstrate that the multifunctional loop and a cross-tetramer contact are important for ATP binding. The evidence supports a view of synapsin I as an ATP-utilizing, tetrameric protein made up of monomers that have a flexible, extended N terminus.
authors.affiliation: Howard Hughes Medical Institute and the Department of Biochemistry, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9050, USA.
authors.forename: Chad A
authors.initials: CA
authors.lastname: Brautigam
authors.forename: Yogarany
authors.initials: Y
authors.lastname: Chelliah
authors.forename: Johann
authors.initials: J
authors.lastname: Deisenhofer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001704:Biopolymers; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D017386:Sequence Homology, Amino Acid; D016704:Synapsins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001704:Biopolymers; D016704:Synapsins; D000255:Adenosine Triphosphate