Regulated secretion in platelets: identification of elements of the platelet exocytosis machinery.
To further characterize the molecular mechanisms of platelet function, we have sought to identify some of the proteins that mediate the secretory events of the platelet release reaction. We report that platelets contain the general elements of the membrane transport apparatus: N-ethylmaleimide sensitive fusion protein (NSF), p115/transcytosis-associated protein (p115/TAP), and the soluble NSF attachment proteins (alpha- and, gamma-SNAP). The cDNAs encoding two of these proteins, alpha- and gamma-SNAP, have been cloned from a human platelet-derived cDNA library. Platelet membrane extracts possess SNAP receptor (SNARE) activity, suggesting that the class of proteins (SNAREs) proposed to provide the specificity for vesicle docking and membrane fusion are present in platelets. To identify these proteins, we have used specific antibodies against known SNAREs to probe platelet extracts. Syntaxin 2 and 4 can be readily detected in platelet membrane preparations and are shown to participate in 20 S complex formation. Syntaxin 1, 3, and 5 could not be detected. Other known SNARE and SNARE-associated proteins such as vesicle-associated membrane protein (VAMP)/synaptobrevin 2, SNAP-25, synaptophysin, or synaptotagmin I could not be immunochemically detected in platelet membrane preparations. The presence of both the general transport proteins (NSF and SNAPs) and specific transport proteins (syntaxin 2 and 4) indicates that platelet exocytosis uses a molecular mechanism similar to other secretory cells such as neurons. However, the subcellular concentrations of these proteins suggest that, unlike neuronal secretion, granule-to plasma membrane docking may be the limiting step in platelet exocytosis.
Lemons
P P
PP
Department of Biochemistry, University of Kentucky College of Medicine, Lexington 40536, USA.
Chen
D
D
Bernstein
A M
AM
Bennett
M K
MK
Whiteheart
S W
SW
D000595:Amino Acid Sequence; D001483:Base Sequence; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics; D003001:Cloning, Molecular; D005089:Exocytosis; D000077614:Golgi Matrix Proteins; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics; D008969:Molecular Sequence Data; D052066:N-Ethylmaleimide-Sensitive Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D016708:Synaptophysin / Q000378:metabolism; D050863:Synaptotagmin I; D050857:Synaptotagmins; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D000077614:Golgi Matrix Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; C494212:STX1A protein, human; C494310:SYT1 protein, human; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D016708:Synaptophysin; D050863:Synaptotagmin I; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D050857:Synaptotagmins; C091580:vesicular transport factor p115; D052066:N-Ethylmaleimide-Sensitive Proteins