NMR STRUCTURE AND MUTAGENESIS OF THE N-TERMINAL DBL HOMOLOGY DOMAIN OF THE NUCLEOTIDE EXCHANGE FACTOR TRIO

Guanine nucleotide exchange factors for the Rho family of GTPases cont ain a Dbl homology (DH) domain responsible for catalysis and a pleckst rin homology (PH) domain whose function is unknown. Here we describe t he solution structure of the N-terminal DH domain of Trio that catalyz es nucleotide exchange for Rac1. The all-alpha-helical protein has a v ery different structure compared to other exchange factors. Based on s ite-directed mutagenesis, functionally important residues of the DH do main were identified. They are all highly conserved and reside in clos e proximity on two alpha helices. In addition, we have discovered a un ique capability of the PH domain to enhance nucleotide exchange in DH domain-containing proteins.