Small GTP-Binding Proteins and Intracellular Messenger Systems

There is a superfamily of ras p21/ras p21-like small GTP-binding proteins(Small G Proteins)with GTPase activity。Over forty members have been reported，and all of them with Mrs between 20，000 and 41，000 are composed of a single respective polypeptide。Evidence is accumulating that small G proteins are involved in intracellular messenger systems.In this research project，We have investigated the post-translational modifications，the modes of activation and the functions of small G proteins.Most of small G proteins have the unique consensus C-terminal motifs containing at least one cysteine residue.We have found that the C-terminal cysteine residues of smg p21B，rhoA p21 and smg p25A are geranygeranylated and that these prenylations are essential for each small G protein to bind to membranes.Small G proteins have two interconvertible forms，GDP-bound inactive and GTP-bound active forms。The conversion from the GDP-bound to GTP-bound form and the reverse conversion are induced by GD…More P/GTP exchange and GTPase reactions，respectively。We have purified and characterized several GDP/GTP exchange proteins(GDP dissociation stimulator(GDS)and GDP Dissociation inhibitor(GDI)and GTPase activating Proteins(GAP)for small G Proteins.GDS and GDI also regulate the binding of small G proteins to membranes.The GTP-bound form small G proteins interact with their specific effector proteins proteins and exert their specific actions.Smg p21B interacts with ras p21GAP and inhibits the ras p21GAP activity for ras p21。Since smg p21B is phosphorylated by protein kinase A，it is conceivable that smg p21B is present in the down stream of protein kinase A.We have also found that smg p25A is detected in regulated secretory cells but not in constitutive secretory cells.Since in most of regulated secretory cells secretion is stimulated by the activation of protein kinase C and the Ca^&lt；2&gt；mobilization，smg p25A might be present in the down stream of protein kinase C and Ca^&lt；2&gt；.These results suggest that small G proteins and their regulatory proteins are regulat ed by well-known intracellular messenger systems and constitute a huge network with them for intracellular regulatory mechanisms.Less：Less

There is a superfamily of ras p21/ras p21-like small GTP-binding proteins (small G proteins) with GTPase activity. Over forty members have been reported, and all of them with Mrs between 20,000 and 41,000 are composed of a single respective polypeptide. Evidence is accumulating that small G proteins are involved in intracellular messenger systems. In this research project, We have investigated the postーtranslational modifications, the modes of activation and the functions of small G proteins. Most of small G proteins have the unique consensus C-terminal motifs containing at least one cysteine residue. We have found that the C-terminal cysteine residues of smg p21B, rhoA p21 and smg p25A are geranygeranylated and that these prenylations are essential for each small G protein to bind to membranes. Small G proteins have two interconvertible forms, GDP-bound inactive and GTP-bound active forms. The conversion from the GDP-bound to GTP-bound form and the reverse conversion are induced by GD … More P/GTP exchange and GTPase reactions, respectively. We have purified and characterized several GDP/GTP exchange proteins (GDP dissociation stimulator (GDS) and GDP Dissociation inhibitor (GDI) ) and GTPase activating Proteins (GAP) for small G Proteins. GDS and GDI also regulate the binding of small G proteins to membranes. The GTP-bound form small G proteins interact with their specific effector proteins proteins and exert their specific actions. Smg p21B interacts with ras p21 GAP and inhibits the ras p21 GAP activity for ras p21. Since smg p21B is phosphorylated by protein kinase A, it is conceivable that smg p 21B is present in the down stream of protein kinase A. We have also found that smg p25A is detected in regulated secretory cells but not in constitutive secretory cells. Since in most of regulated secretory cells secretion is stimulated by the activation of protein kinase C and the Ca^<2+> mobilization, smg p25A might be present in the down stream of protein kinase C and Ca^<2+>. These results suggest that small G proteins and their regulatory proteins are regulat ed by well-known intracellular messenger systems and constitute a huge network with them for intracellular regulatory mechanisms. Less