Regulation of the GTPase activity of the ras-like protein p25rab3A. Evidence for a rab3A-specific GAP.
The rab3A gene product is a 25-kilodalton guanine nucleotide-binding protein, expressed at high levels in neural tissue, which has about 30% homology to ras. Recombinant rab3A protein and p25rab3A purified from bovine brain membranes have been used as substrates to look for factors that regulate its biochemical activity. A detergent-soluble factor associated with rat brain membranes exists that accelerates the GTPase activity of both mammalian and recombinant p25rab3A. The activity was thermolabile, sensitive to trypsin, and behaved like an integral membrane protein. GTPase-activating protein (GAP) activity toward p25rab3A was also detected in the cytosolic fraction. This activity was observed in all other tissues examined, in addition to brain. Based upon dose-response data, the rab3A-GAP activity from rat brain was approximately equally distributed between cytosolic and membrane fractions; no activity was found in the nuclear fraction. Recombinant ras-specific GAP had no effect upon the GTPase activity of p25rab3A. By gel filtration chromatography, the factor in rat brain cytosol has a molecular size of 400,000 daltons.
Burstein
E S
ES
Department of Biophysics, University of Rochester Medical Center, New York 14642.
Linko-Stentz
K
K
Lu
Z J
ZJ
Macara
I G
IG
D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000201:enzymology; D002384:Catalysis; D002850:Chromatography, Gel; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051381:Rats; D014357:Trypsin; D020692:rab3 GTP-Binding Proteins
D009419:Nerve Tissue Proteins; D014357:Trypsin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins