Tetramerization and ATP Binding by a Protein Comprising the A, B, and C Domains of Rat Synapsin I

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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.

Original languageEnglish (US)
Pages (from-to)11948-11956
Number of pages9
JournalJournal of Biological Chemistry
Issue number12
StatePublished - Mar 19 2004

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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