Interactions between Rho GTPases and Rho GDP dissociation inhibitor (Rho-GDI)

The Rho-GDP dissociation inhibitor (Rho-GDI) was used as bait in a two-hybr id screen of a human leucocyte cDNA library. Most of the isolated cDNAs enc oded GTPases of the Rho subfamily: RhoA, B, C, Rac1, 2, CDC42 and RhoG. The newly discovered RhoH interacted very poorly with Rho-GDI. Another protein partner shared a homology with RhoA that points to Asp67(RhoA)-Ar68(RhoA)- Leu69(RhoA) as critical for interaction with Rho-GDI. A second screen with RhoA as bait led to the isolation of GDI only. In order to investigate the relative role of protein-protein and protein-lipid interactions between Rho GTPases and Rho-GDI, CAAX box mutants of RhoA were produced. They were fou nd to interact with Rho-GDI as efficiently as wild type RhoA, indicating th at protein-protein interactions alone lead to strong binding of the two pro teins. The C-terminal polybasic region of RhoA was also shown to be a site of protein-protein interaction with Rho-GDI. (C) 2001 Societe francaise de biochimie et biologie moleculaire/Editions scientifiques et medicales Elsev ier SAS. All rights reserved.