H-Ras
(5p21)

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I. Introduction

H-Ras is a protypical example of a small G protein which binds GTP and which has GTPase activity.  This signaling is active in the GTP bound state, and inactive in the GDP bound state.

For more information see Biochemistry Online: Chapter 9C-7 - Small G proteins, GAPs and GEFs

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II. General Structure

The superfamily of small G proteins have a common 20K molecular weight catalytic domain with 5 alpha helices, 6 beta strands and connecting loops.  The G1 loop binds phosphate groups as is often called the P-loop (as in the case of protein tyrosine phosphatases).  Its binds GTP and GDP and has GTPase activity.  The small G proteins are "active" in the GTP bound form.  Hydrolysis of GTP to GDP causes the protein to become inactive in signaling pathways.

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