Fusion of membranes during the acrosome reaction: a tale of two SNAREs.
During spermiogenesis, hydrolytic enzymes are sorted from the Golgi apparatus to the acrosome, a supranuclear megavesicle. At fertilization, the enzymatic content of the acrosome is released by exocytosis when a portion of the plasma membrane enveloping the sperm head fuses with the outer membrane of the acrosome. Membrane fusion involves the interaction of a specific pair of proteins, called SNAREs (for soluble N-ethylmaleimide sensitive factor attachment protein receptor). v-SNARE is presumably associated with the membrane of the acrosomal vesicle. Target t-SNARE is associated with the plasma membrane. The interaction of v-SNARE and t-SNARE requires two additional proteins: Rab proteins, members of a family of small GTPases related to the Ras proteins, and a complex of two proteins, NSF-SNAP, recruited by the interacting v-SNARE-tSNARE pair. Syntaxin 2, a v-SNARE member, and Rab3A, a member of the Rab GTPases, have been localized in the acrosome of rodent sperm.
Kierszenbaum
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Department of Cell Biology and Anatomical Sciences, The City University of New York Medical School, New York, NY 10031, USA. kier@med.cuny.edu
D020101:Acrosome Reaction / Q000502:physiology*; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D022181:COP-Coated Vesicles / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D008297:Male; D008561:Membrane Fusion / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D050600:SNARE Proteins; D013091:Spermatogenesis / Q000502:physiology; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D020826:rab3A GTP-Binding Protein / Q000378:metabolism*
D000954:Antigens, Surface; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D020826:rab3A GTP-Binding Protein