Single Molecule Processivity of SOS-cat, the Catalytic Core of the Ras Gef ‘son of Sevenless’

摘要: The Ras GEF Son of Sevenless (SOS) activates the membrane-anchored G-protein by catalyzing replacement bound GDP with GTP. We have previously shown that in addition to catalytic site, SOS has a catalytically inactive allosteric binding site for Ras, which allows localize and up-concentrate at presenting membranes, dramatically increasing Ras-GDP turnover rate. Together, sites form core (SOScat).In present work we use TIRF fluorescence microscopy show vitro, single SOScat enzymes can be highly processive, remaining surface via while turning over hundreds thousands site.By confining individual micron-scale two-dimensional supported lipid bilayer ‘reaction chambers’ monitor arrays enzymes, probing variability rate processivity within enzyme ensemble. only small fraction are this is modulated nucleotide state Ras-GTP promoting higher processive than Ras-GDP.