Learning from Bacteria: Molecular Chaperones in Ribosomes and Thermophilic Adaptation

In this chapter, we review two topics, protein biosynthesis and thermophilic adaptation. Protein biosynthesis is of central importance for all living systems. The process of polypeptide translation and the subsequent modifications leading to the final three-dimensional protein structure are highly complex biochemical reactions that involve many components. Even in normal growth conditions, some heat-shock proteins (HSPs) bind to ribosomes and the ribosomebound nascent chain to prevent misfolding and aggregation of nascent chains. Under heat stress, the amounts of these HSPs are increased and other HSPs are newly induced and bind to the ribosomes. In addition to HSPs, constitutive components of ribosomes have chaperone activity and may contribute to ribosome assembly and biosynthesis and folding of nascent chains. It has become clear that the biosphere contains a variety of microorganisms that can live and grow in extreme environments. Thermophilic microorganisms proliferate at temperatures of more than 60°C (for hyperthermophilic microorganisms, more than 80°C). To grow at extreme conditions microorganisms require adaptive mechanisms. The results of current studies on these microorganisms provide information about the unique properties of molecular factors that impart stability to thermostable biomolecules.