title: Crystal structure of the rac activator, Asef, reveals its autoinhibitory mechanism.
abstract: The Rac-specific guanine nucleotide exchange factor (GEF) Asef is activated by binding to the tumor suppressor adenomatous polyposis coli mutant, which is found in sporadic and familial colorectal tumors. This activated Asef is involved in the migration of colorectal tumor cells. The GEFs for Rho family GTPases contain the Dbl homology (DH) domain and the pleckstrin homology (PH) domain. When Asef is in the resting state, the GEF activity of the DH-PH module is intramolecularly inhibited by an unidentified mechanism. Asef has a Src homology 3 (SH3) domain in addition to the DH-PH module. In the present study, the three-dimensional structure of Asef was solved in its autoinhibited state. The crystal structure revealed that the SH3 domain binds intramolecularly to the DH domain, thus blocking the Rac-binding site. Furthermore, the RT-loop and the C-terminal region of the SH3 domain interact with the DH domain in a manner completely different from those for the canonical binding to a polyproline-peptide motif. These results demonstrate that the blocking of the Rac-binding site by the SH3 domain is essential for Asef autoinhibition. This may be a common mechanism in other proteins that possess an SH3 domain adjacent to a DH-PH module.
authors.affiliation: Tohoku University Biomedical Engineering Research Organization, Sendai 980-8575; RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Murayama
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Mikako
authors.initials: M
authors.lastname: Shirouzu
authors.affiliation: Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0033, and the.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kawasaki
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Miyuki
authors.initials: M
authors.lastname: Kato-Murayama
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Hanawa-Suetsugu
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Ayako
authors.initials: A
authors.lastname: Sakamoto
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Katsura
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Suenaga
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Toyama
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Takaho
authors.initials: T
authors.lastname: Terada
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.
authors.forename: Makoto
authors.initials: M
authors.lastname: Taiji
authors.affiliation: Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0033, and the.
authors.forename: Tetsu
authors.initials: T
authors.lastname: Akiyama
authors.affiliation: RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045; Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033 Japan. Electronic address: yokoyama@biochem.s.u-tokyo.ac.jp.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D002465:Cell Movement; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009154:Mutation; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors; D040681:Structural Homology, Protein; D020663:ras Guanine Nucleotide Exchange Factors / Q000378:metabolism; D018909:src Homology Domains
chemical_list: C576602:ARHGEF4 protein, human; D025601:Adenomatous Polyposis Coli Protein; D020662:Guanine Nucleotide Exchange Factors; C057811:MCF2 protein, human; D010455:Peptides; D011518:Proto-Oncogene Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; D020663:ras Guanine Nucleotide Exchange Factors; C011083:polyproline