13] Chaperonins of the purple nonsulfur bacterium Rhodobacter sphaeroides

Abstract

Publisher Summary The chapter presents a study related to the chaperonins of the purple nonsulfur bacterium Rhodobacter sphaeroides. The purple nonsulfur bacterium Rhodobacter sphaeroides is a metabolically versatile organism capable of being cultured under widely different growth conditions. Used as a model to study the regulation and biochemistry of carbon fixation in prokaryotes, R. sphaeroides , possesses two ribulose-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) enzymes. Rubisco, the key enzyme of the Calvin reductive pentose phosphate pathway, is a multimeric enzyme that has been demonstrated to require chaperonins for folding and subsequent assembly both in vivo and in vitro . The Escherichia coli and R. sphaeroides cpn60s have 68% identity, and several of the key amino acid residues identified in the E. coli protein are conserved in the R. sphaeroides cpn60. Of the 14 E. coli cpn60 amino acid residues identified by site-directed mutagenesis that are involved in ATP hydrolysis are conserved in R. sphaeroides cpn60. Similarly, most of the residues involved in E. coli GroEL binding, polypeptide binding, and folding of heterologous proteins are conserved in the R. sphaeroides cpn60. The relationships between cpn60s of diverse eubacteria show that the R. sphaeroides cpn60 is most closely related to proteins from α subdivision of the purple bacteria.