Complexin/Synaptotagmin Interplay Controls Acrosomal Exocytosis

ROGGERO, CARLOS M.; DE BLAS, GERARDO A.; DAI, HAN; TOMES, CLAUDIA N.; RIZO, JOSEP; MAYORGA, LUIS S.

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Año: 2007 vol. 282 p. 26335 - 26343

0021-9258

Regulated secretion is a fundamental process underlying thefunction of many cell types. In particular, acrosomal exocytosisin mammalian sperm is essential for egg fertilization. Regulatedsecretion requires SNARE proteins and, in neurons, also synaptotagminI and complexin. Recent reports suggest that complexinimposes a fusion block that is released by Ca2 and synaptotagminI. However, no direct evidence for this model insecreting cells has been provided and whether this complexin/synaptotagmin interplay functions in other types of secretion isunknown. In this report, we show that the C2B domain of synaptotagminVI and an anti-complexin antibody blocked the formationof trans SNARE complexes in permeabilized humansperm, and that this effect was reversed by adding complexin. Incontrast, an excess of complexin stopped exocytosis at a laterstep, when SNAREs were assembled in loose trans complexes.Interestingly, this blockage was released by the addition of thesynaptotagmin VI C2B domain in the presence of Ca2.We havepreviously demonstrated that the activity of this domain is regulatedby protein kinase C-mediated phosphorylation. Here, weshow that a phosphomimetic mutation in the polybasic region ofthe C2B domain strongly affects its Ca2 and phospholipidsbinding properties. Importantly, this mutation completelyabrogates its ability to rescue the complexin block. Our resultsshow that the functional interplay between complexin and synaptotagminhas a central role in a physiological secretion event,and that this interplay can be modulated by phosphorylation ofthe C2B domain.