Barnase and Barstar

Publisher Summary This chapter provides an overview of two small bacterial proteins, barnase and barstar. Barnase is a ribonuclease, and barstar is its specific inhibitor. Barnase, an extracellular enzyme secreted by Bacillus amyloliquefaciens strain H (IAM1521), is one of a family of small microbial ribonucleases. Known homologs, in addition to those from other species of Bacillus , include products of several Streptomyces strains and the group of fungal enzymes related to ribonuclease T1. Barstar is an even smaller protein, with 89 amino acids. Produced intracellularly by the same organism, it is a specific inhibitor of barnase. Although barstar has two cysteine residues, it is now clear that these do not form a disulfide bond and probably carry free sulfhydryls in vivo . Barstar (CCAA), a mutant with alanines in place of its two cysteines, is functional in vitro and in vivo . This chapter discusses the gene structure of barnase and barstar. It explains concepts related to barnase–barstar complex and barnase–barstar reaction. It also describes barnase, barstar, and the folding problem. The chapter elaborates in detail about barnase and barstar homologs. The chapter concludes with a discussion on practical applications of barnase.