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Vol. 20, Issue 24, 5086-5095, December 15, 2009

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Phosphatidylserine Regulation of Ca²⁺-triggered Exocytosis and Fusion Pores in PC12 Cells

Zhen Zhang^*, Enfu Hui^,, Edwin R. Chapman, and Meyer B. Jackson

*Molecular and Cellular Pharmacology Graduate Program, Program in Biophysics, Howard Hughes Medical Institute, and Department of Physiology, University of Wisconsin School of Public Health, Madison, WI 53706

Submitted August 14, 2009; Revised September 22, 2009; Accepted October 7, 2009
Monitoring Editor: Patrick J. Brennwald

The synaptic vesicle protein synaptotagmin I (Syt I) binds phosphatidylserine (PS) in a Ca²⁺-dependent manner. This interaction is thought to play a role in exocytosis, but its precise functions remain unclear. To determine potential roles for Syt I-PS binding, we varied the PS content in PC12 cells and liposomes and studied the effects on the kinetics of exocytosis and Syt I binding in parallel. Raising PS produced a steeply nonlinear, saturating increase in Ca²⁺-triggered fusion, and a graded slowing of the rate of fusion pore dilation. Ca²⁺-Syt I bound liposomes more tightly as PS content was raised, with a steep increase in binding at low PS, and a further gradual increase at higher PS. These two phases in the PS dependence of Ca²⁺-dependent Syt I binding to lipid may correspond to the two distinct and opposing kinetic effects of PS on exocytosis. PS influences exocytosis in two ways, enhancing an early step leading to fusion pore opening, and slowing a later step when fusion pores dilate. The possible relevance of these results to Ca²⁺-triggered Syt I binding is discussed along with other possible roles of PS.

Address correspondence to: Meyer B. Jackson (mjackson{at}physiology.wisc.edu).

Abbreviations used: FRET, fluorescence resonance energy transfer; PS, phosphatidylserine; PSF, prespike foot; PSS, phosphatidylserine synthase.

This article has been cited by other articles:

				Z. Zhang, E. Hui, E. R. Chapman, and M. B. Jackson Regulation of Exocytosis and Fusion Pores by Synaptotagmin-Effector Interactions Mol. Biol. Cell, August 15, 2010; 21(16): 2821 - 2831. [Abstract] [Full Text] [PDF]