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PIP2 increases the speed of response of synaptotagmin and steers its membrane-penetration activity toward the plasma membrane

Nature Structural & Molecular Biology volume 11, pages 36–44 (2004)Cite this article

Abstract

Synaptotagmin-1 (syt), the putative Ca2+ sensor for exocytosis, is anchored to the membrane of secretory organelles. Its cytoplasmic domain is composed of two Ca2+-sensing modules, C2A and C2B. Syt binds phosphatidylinositol 4,5-bisphosphate (PIP2), a plasma membrane lipid with an essential role in exocytosis and endocytosis. We resolved two modes of PIP2 binding that are mediated by distinct surfaces on the C2B domain of syt. A novel Ca2+-independent mode of binding predisposes syt to penetrate PIP2-harboring target membranes in response to Ca2+ with submillisecond kinetics. Thus, PIP2 increases the speed of response of syt and steers its membrane-penetration activity toward the plasma membrane. We propose that syt-PIP2 interactions are involved in exocytosis by facilitating the close apposition of the vesicle and target membrane on rapid time scales in response to Ca2+.

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Figure 1: Two distinct modes of syt-PIP2 interactions.
Figure 2: Mechanism and kinetics of Ca2+-triggered syt-PIP2 interactions.
Figure 3: Specialization of the C2 domains of syt.
Figure 4: PIP2 increases the speed of response of syt.
Figure 5: Steady-state quenching experiments confirm that PIP2 steers the membrane-penetration activity of syt.
Figure 6: Membrane-embedded syt binds, in trans, to acceptor liposomes containing PIP2.
Figure 7: Quantification of trans syt-membrane interactions.

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Acknowledgements

We thank J.M. Edwardson, T.F.J. Martin, M. Jackson and C.T. Wang for helpful discussions, and R. Jahn and S. Engers for synaptobrevin-2 antibodies. This study was supported by grants from the US National Institutes of Health (National Institute of General Medical Sciences GM 56827 and National Institute of Mental Health MH61876), American Heart Association (AHA) 9750326N and the Milwaukee Foundation. E.R.C. is a Pew Scholar in the Biomedical Sciences. J.B. is supported by an AHA predoctoral Fellowship.

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  1. Department of Physiology, University of Wisconsin, Madison, 53706, Wisconsin, USA

    Jihong Bai, Ward C Tucker & Edwin R Chapman

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Correspondence to Edwin R Chapman.

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Bai, J., Tucker, W. & Chapman, E. PIP2 increases the speed of response of synaptotagmin and steers its membrane-penetration activity toward the plasma membrane. Nat Struct Mol Biol 11, 36–44 (2004). https://doi.org/10.1038/nsmb709

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