Synaptotagmin I is a high affinity receptor for clathrin AP-2: implications for membrane recycling.
In nerve terminals, Ca(2+)-stimulated synaptic vesicle exocytosis is rapidly followed by endocytosis. Synaptic vesicle endocytosis requires clathrin-coated pits similar to receptor-mediated endocytosis in fibroblasts. Binding of clathrin AP-2 (adaptor complex) to an unidentified high affinity membrane receptor appears to be necessary for coated pit assembly in fibroblasts. We now show that synaptic vesicles have a high affinity AP-2 site (KD, approximately 1 x 10(-10) M) similar to the one observed in fibroblasts. Using a combination of competition and direct binding assays, we demonstrate that synaptotagmin I, an intrinsic membrane protein of synaptic vesicles, has all of the properties of the AP-2 receptor and that AP-2 binds to the second C2 domain in the molecule. Thus, synaptotagmin I may be a multifunctional protein with a function in endocytosis in addition to the previously proposed role in exocytosis.
Zhang
J Z
JZ
Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas 75235.
Davletov
B A
BA
Südhof
T C
TC
Anderson
R G
RG
D033942:Adaptor Proteins, Vesicular Transport; D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D016764:Cell Polarity; D002966:Clathrin / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004705:Endocytosis; D005089:Exocytosis; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D013572:Synaptic Vesicles / Q000378:metabolism*; D050863:Synaptotagmin I; D050857:Synaptotagmins
D033942:Adaptor Proteins, Vesicular Transport; D002135:Calcium-Binding Proteins; D002966:Clathrin; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D050863:Synaptotagmin I; D050857:Synaptotagmins; D000255:Adenosine Triphosphate