Kinetic analysis of the guanine nucleotide exchange activity of TRAPP, a multimeric Ypt1p exchange factor.

ABSTRACT: TRAPP complexes, which are large multimeric assemblies that function in membrane traffic, are guanine nucleotide exchange factors (GEFs) that activate the Rab GTPase Ypt1p. Here we measured rate and equilibrium constants that define the interaction of Ypt1p with guanine nucleotide (guanosine 5'-diphosphate and guanosine 5'-triphosphate/guanosine 5'-(beta,gamma-imido)triphosphate) and the core TRAPP subunits required for GEF activity. These parameters allowed us to identify the kinetic and thermodynamic bases by which TRAPP catalyzes nucleotide exchange from Ypt1p. Nucleotide dissociation from Ypt1p is slow (approximately 10(-4) s(-1)) and accelerated >1000-fold by TRAPP. Acceleration of nucleotide exchange by TRAPP occurs via a predominantly Mg(2+)-independent pathway. Thermodynamic linkag

SUBMITTER: Chin HF 

PROVIDER: S-EPMC2770256 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature