The evolutionary pressure to inactivate: A subclass of synaptotagmins with an amino acid substitution that abolishes Ca2+ binding

Christine Von Poser, Konstantin Ichtchenko, Xuguang Shao, Jose Rizo-Rey, Thomas C. Südhof

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Abstract

Synaptotagmin I is a Ca2+-binding protein of synaptic vesicles that serves as a Ca2+ sensor for neurotransmitter release and was the first member found of a large family of trafficking proteins. We have now identified a novel synaptotagmin, synaptotagmin XI, that is highly expressed in brain and at lower levels in other tissues. Like other synaptotagmins, synaptotagmin XI has a single transmembrane region and two cytoplasmic Ca- domains but is most closely related to synaptotagmin IV with which it forms a new subclass of synaptotagmins. The first C2-domain of synaptotagmin I (the C2A-domain) binds phospholipids as a function of Ca2+ and contains a Ca2+-binding site, the C2-motif, that binds at least two Ca2+ ions via five aspartate residues and is conserved in most C2-domains (Shao, X., Davletov, B., Sutton, B., Sudhof, T. C., Rizo, J. R. (1996) Science 273, 248- 253). In the C2A-domains of synaptotagmins IV and XI, however, one of the five Ca2+-binding aspartates in the C2-motif is substituted for a serine, suggesting that these C2-domains do not bind Ca2+. To test this, we produced recombinant C2A-domains from synaptotagmins IV and XI with either wild type serine or mutant aspartate in the C2-motif. Circular dichroism showed that Ca2+ stabilizes both mutant but not wild type C2-domains against temperature-induced denaturation, indicating that the mutations restore Ca2+-binding to the wild type C2-domains. Furthermore, wild type C2A-domains of synaptotagmins IV and XI exhibited no Ca2+-dependent phospholipid binding, whereas mutant C2A-domains bound phospholipids as a function of Ca2+ similarly to wild type synaptotagmin I. These experiments suggest that a class of synaptotagmins was selected during evolution in which the Ca2+-binding site of the C2A-domain was inactivated by a single point mutation. Thus, synaptotagmins must have Ca2+-independent functions as well as Ca2+-dependent functions that are selectively maintained in distinct members of this gene family.

Original languageEnglish (US)
Pages (from-to)14314-14319
Number of pages6
JournalJournal of Biological Chemistry
Volume272
Issue number22
DOIs
StatePublished - May 30 1997

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Synaptotagmins
Amino Acid Substitution
Substitution reactions
Amino Acids
Pressure
Synaptotagmin I
Aspartic Acid
Phospholipids
Serine
Binding Sites
Denaturation
Synaptic Vesicles
Protein Transport
Circular Dichroism

ASJC Scopus subject areas

  • Biochemistry

Cite this

The evolutionary pressure to inactivate : A subclass of synaptotagmins with an amino acid substitution that abolishes Ca2+ binding. / Von Poser, Christine; Ichtchenko, Konstantin; Shao, Xuguang; Rizo-Rey, Jose; Südhof, Thomas C.

In: Journal of Biological Chemistry, Vol. 272, No. 22, 30.05.1997, p. 14314-14319.

Research output: Contribution to journalArticle

Von Poser, Christine ; Ichtchenko, Konstantin ; Shao, Xuguang ; Rizo-Rey, Jose ; Südhof, Thomas C. / The evolutionary pressure to inactivate : A subclass of synaptotagmins with an amino acid substitution that abolishes Ca2+ binding. In: Journal of Biological Chemistry. 1997 ; Vol. 272, No. 22. pp. 14314-14319.
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