New experimental approaches for investigating interactions between Pyrococcus furiosus carbamate kinase and carbamoyltransferases, enzymes involved in the channeling of thermolabile carbamoyl phosphate

摘要

A somewhat neglected but essential aspect of the molecular physiology of hyperthermophiles is the protection of thermolabile metabolites and coenzymes. An example is carbamoyl phosphate (CP). a precursor of pyrimidines and arginine, which is an extremely labile and potentially toxic intermediate. The first evidence for a biologically significant interaction between carbamate kinase (CK) and ornithine car-bamoyltransferase (OTC) from Pyrococcus furiosus was provided by affinity electrophoresis and eo-immunoprecipitation in combination with cross-linking (Massantetal. 2002). Using the yeast two-hybrid system, Hummel-Dreyer chromatogra-phy and isothermal titration calorimetry, we obtained additional concrete evidence for an interaction between CK and OTC. the first evidence for an interaction between CK and aspartate carbamoyltransferase (ATC) and an estimate of the binding constant between CK and ATC. The physical interaction between CK and OTC or ATC may prevent thermodena-turation of CP in the aqueous cytoplasmic environment. Here we emphasize the importance of developing experimental approaches to investigate the mechanism of thermal protection of metabolic intermediates by metabolic channeling and the molecular basis of transient protein-protein interactions in the physiology of hyperthermophiles.