Membrane permeant Rab3A triggers acrosomal exocytosis in the absence of extracellular calcium.

C.I. LÓPEZ, S.A. BELMONTE, G.A. DE BLAS, L.S. MAYORGA

Pinamar, Buenos Aires

Congreso; X Congreso PABMB, XLI REUNIÓN ANUAL SOCIEDAD ARGENTINA DE INVESTIGACIÓN BIOQUÍMICA Y BIOLOGÍA MOLECULAR, XX Reunión Anual SAN; 2005

SAIB

Acrosome reaction (AR) is a regulated exocytosis in which the outer acrosomal and plasma membrane fuse and the acrosome content is released. To study the function of fusion factors during AR, we have been working in streptolysin O-permeabilized human sperm. To establish a more physiological model, we have recently developed an arginine-rich peptide that, when linked to proteins, permits the diffusion of these molecules through the plasma membrane. GST and the small GTPase Rab3A linked to the peptide RRRQRRKRRRQ (GST-R and R-Rab3A respectively) added to the extracellular medium entered into non permeabilized sperm. Moreover, R-Rab3A induced AR when loaded with GTPgS but not when loaded with GDPbS. Similar to what we have described in permeabilized sperm using Rab3A, the action of R-Rab3A was modulated by the cholesterol content of membranes. Interestingly, R-Rab3A mediated AR stimulation does not require extracellular calcium but depends on IP3 sensitive calcium channels.  Our results indicate that membrane permeant proteins such as R-Rab3A will be powerful tools to study the physiology of sperm AR.