Interaction of a novel fluorescent GTP analogue with the small G-protein K-Ras

A novel fluorescent guanosine 50-triphosphate (GTP) analogue, 20(30)-O-{6-(N-(7-nitrobenz-2-oxa-l,3-diazol-4-yl)amino) hexanoic}-GTP (NBD-GTP), was synthe-sized and utilized to monitor the effect of mutations in the functional region of mouse K-Ras. The effects of the G12S, A59T and G12S/A59T mutations on GTPase activity, nucleotide exchange rates were com-pared with normal Ras. Mutation at A59T resulted in reduction of the GTPase activity by 0.6-fold and en-hancement of the nucleotide exchange rate by 2-fold compared with normal Ras. On the other hand, muta-tion at G12S only slightly affected the nucleotide ex-change rate and did not affect the GTPase activity. We also used NBD-GTP to study the effect of these mu-tations on the interaction between Ras and SOS1, a guanine nucleotide exchange factor. The mutation at A59T abolished the interaction with SOS1. The results suggest that the fluorescent GTP analogue, NBD-GTP, is applicable to the kinetic studies for small G-proteins