title: Structure, exchange determinants, and family-wide rab specificity of the tandem helical bundle and Vps9 domains of Rabex-5.
abstract: The Rab5 GTPase, an essential regulator of endocytosis and endosome biogenesis, is activated by guanine-nucleotide exchange factors (GEFs) that contain a Vps9 domain. Here, we show that the catalytic core of the Rab GEF Rabex-5 has a tandem architecture consisting of a Vps9 domain stabilized by an indispensable helical bundle. A family-wide analysis of Rab specificity demonstrates high selectivity for Rab5 subfamily GTPases. Conserved exchange determinants map to a common surface of the Vps9 domain, which recognizes invariant aromatic residues in the switch regions of Rab GTPases and selects for the Rab5 subfamily by requiring a small nonacidic residue preceding a critical phenylalanine in the switch I region. These and other observations reveal unexpected similarity with the Arf exchange site in the Sec7 domain.
authors.affiliation: Program in Molecular Medicine and Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Delprato
authors.forename: Eric
authors.initials: E
authors.lastname: Merithew
authors.forename: David G
authors.initials: DG
authors.lastname: Lambright
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain / Q000502:physiology; D004705:Endocytosis / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010649:Phenylalanine / Q000737:chemistry; D011485:Protein Binding / Q000502:physiology*; D017433:Protein Structure, Secondary / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: C438187:ALS2 protein, human; D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; C108382:RABGEF1 protein, human; C092117:RIN1 protein, human; D010649:Phenylalanine; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins