G proteins and low-molecular-weight GTP-binding proteins in platelets.
Platelets contain at least two distinct families of proteins that can bind GTP: the G proteins and the low-molecular-weight GTP-binding proteins. G proteins are heterotrimeric regulatory proteins that mediate the interaction between cell surface receptors and the enzymes that generate second messengers during platelet activation. At least five different G proteins have been identified in platelets. The low-molecular-weight GTP-binding proteins range in size from 21 to 28 kDa. Little is known for certain about their function, but at least 15 such proteins have been identified in platelets, many of which have been shown to be homologous to the products of the ras protooncogene. In cells other than platelets, low-molecular-weight GTP-binding proteins have been implicated in protein transport, cell activation events, and malignant transformation. Their role in platelets is unknown.
Departments of Medicine and Pathology, University of Pennsylvania, Philadelphia, PA 19104, USA.
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Manning