Leucine zipper-mediated homodimerization of the p21-activated kinase-interacting factor, beta Pix. Implication for a role in cytoskeletal reorganization.
Pix, a p21-activated kinase-interacting exchange factor, is known to be involved in the regulation of Cdc42/Rac GTPases. The 85-kDa betaPix-a protein contains an Src homology 3 domain, the tandem Dbl homology and Pleckstrin homology domains, a proline-rich region, and a GIT1-binding domain. In addition to those domains, betaPix-a also contains a putative leucine zipper domain at the C-terminal end. In this study, we demonstrate that the previously identified putative leucine zipper domain mediates the formation of betaPix-a homodimers. Using in vitro and in vivo methodologies, we show that deletion of the leucine zipper domain is sufficient to abolish betaPix-a homodimerization. In NIH3T3 fibroblast cells, expression of wild type betaPix-a induces the formation of membrane ruffles. However, cells expressing the leucine zipper domain deletion mutant could not form membrane ruffle structures. Moreover, platelet-derived growth factor-mediated cytoskeletal changes were completely blocked by the leucine zipper domain deletion mutant. The results suggest that the leucine zipper domain enables betaPix-a to homodimerize, and homodimerization is essential for betaPix-a signaling functions leading to the cytoskeletal reorganization.
School of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea. depark@snu.ac.kr
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D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D019281:Dimerization; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D016350:Leucine Zippers; D051379:Mice; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D020741:rho GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*
C576607:Arhgef7 protein, mouse; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D064067:Rho Guanine Nucleotide Exchange Factors; D017346:Protein Serine-Threonine Kinases; D020741:rho GTP-Binding Proteins