title: Vps9, Rabex-5 and DSS4: proteins with weak but distinct nucleotide-exchange activities for Rab proteins.
abstract: The activities of three Rab-specific factors with GDP/GTP exchange activity, Vps9p, Rabex-5 and DSS4, with their cognate GTPases, Ypt51p, Rab5 and Ypt1p, have been analysed quantitatively. In contrast to other exchange factors examined and to DSS4, Vps9p, and by analogy probably Rabex-5, have considerably lower affinity than GDP to the respective GTPases. In keeping with this, they are relatively weak exchangers, with a maximal rate constant for GDP release from the ternary complex between exchange factor, GTPase and GDP of ca 0.01 s(-1), which is several orders of magnitude lower than for other exchange factors examined. If interaction with these proteins is a mandatory aspect of the Rab cycle, this suggests that the overall rate of cycling might be controlled at this point of the cycle. Surprisingly, DSS4, which has the thermodynamic potential to displace GDP effectively from Ypt1p, also does this very slowly, again with a maximal rate constant of ca 0.01 s(-1). An additional, and based on present knowledge, unique, feature of the Ypt1p.DSS4 complex, is that the association of GTP (or GDP) is more than 10(3)-fold slower than to Ypt1p, thus leading to a long life-time of the binary complex between the two proteins, even at the high nucleotide concentrations that prevail in the cell. This leads to the conclusion that the protein-protein complex is likely to have an important biological significance in addition to its probable role in GTP/GDP exchange.
authors: Department of Physical Biochemistry, Max-Planck Institute for Molecular Physiology, Otto-Hahn-Strasse 11, Dortmund, 44227, Germany.
authors: H
authors: H
authors: Esters
authors: K
authors: K
authors: Alexandrov
authors: A
authors: A
authors: Iakovenko
authors: T
authors: T
authors: Ivanova
authors: N
authors: N
authors: Thomä
authors: V
authors: V
authors: Rybin
authors: M
authors: M
authors: Zerial
authors: A J
authors: AJ
authors: Scheidig
authors: R S
authors: RS
authors: Goody
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D004735:Energy Transfer; D005453:Fluorescence; D005656:Fungal Proteins / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D009282:Naphthalenesulfonates; D011485:Protein Binding; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D013816:Thermodynamics; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C079548:DSS4 protein, S cerevisiae; D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D009282:Naphthalenesulfonates; C108382:RABGEF1 protein, human; D029701:Saccharomyces cerevisiae Proteins; C099285:VPS9 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D006153:Guanosine Diphosphate; C006421:1,5-I-AEDANS; D006160:Guanosine Triphosphate; C086866:VPS21 protein, S cerevisiae; C060755:YPT1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins