title: Structural analysis of the SH3 domain of beta-PIX and its interaction with alpha-p21 activated kinase (PAK).
abstract: The PAK Ser/Thr kinases are important downstream effectors of the Rho family GTPases Cdc42 and Rac, partly mediating the role of these G proteins in cell proliferation and cytoskeletal rearrangements. As well as small G proteins, PAK interacts with the Cdc42/Rac exchange factor beta-PIX via the PIX SH3 domain and a nontypical Pro-rich region in PAK. This interaction is thought to affect the localization of PAK, as well as increased GTP/GDP exchange of Rac and Cdc42. We have determined the structure of the PIX-SH3/PAK peptide complex and shown that it differs from typical Src-like SH3/peptide complexes. The peptide makes contacts through the Pro-rich sequence in a similar way to standard SH3/peptide complexes, even though the Pro residue positions are not conserved. In addition, there are interactions with a Pro and Lys in the PAK, which are C-terminal to the conserved Arg found in all SH3-binding sequences. These contact a fourth binding pocket on the SH3 domain. We have measured the affinity of PIX-SH3 for the PAK peptide and found that it is of intermediate affinity. When PAK is activated, Ser-199 in the PIX-binding site is phosphorylated. This phosphorylation is sufficient to reduce the affinity for PIX 6-fold.
authors.affiliation: Department of Biochemistry, University of Cambridge, UK. mott@bioc.cam.ac.uk
authors.forename: Helen R
authors.initials: HR
authors.lastname: Mott
authors.forename: Daniel
authors.initials: D
authors.lastname: Nietlispach
authors.forename: Katrina A
authors.initials: KA
authors.lastname: Evetts
authors.forename: Darerca
authors.initials: D
authors.lastname: Owen
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction / Q000502:physiology; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D018909:src Homology Domains / Q000502:physiology
chemical_list: C576606:ARHGEF7 protein, human; D000596:Amino Acids; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D010455:Peptides; D064067:Rho Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins