Methanocaldococcus jannaschii GMP synthetase : investigations on aspects of catalysis and the role of an unusual posttranslational modification in structure and function

Abstract

"This chapter describes key features of glutamine amidotransferases (GATs). Glutamine amidotransferases are the enzymes that transfer ammonia derived from glutamine to various acceptor substrates. Apart from having a central role in metabolism and their potential as drug targets, these enzymes have been an area of active investigation for many decades for their fascinating biochemistry. Large conformational dynamics, coordinated domain-cross talk and ammonia channeling are some of the defining features of this family of enzymes. Amidotransferases are represented by a large group of enzymes and have been classified into three classes. A brief account of their classification along with their role in various biosynthetic pathways is presented in this chapter. GMP synthetase (GMPS), one of the members of this family of enzymes is the subject of the present study. GMP synthetase catalyzes the conversion of XMP to GMP. The enzyme contains two distinct catalytic sites, GATase (site for ammonia production from glutamine) and ATPPase (the site for XMP amination). The two sites are present in two domains within a single polypeptide chain as in all prokaryotic, eukaryotic and a few members of archaeal GMPS. In most archaeal GMP synthetases, the two sites are present in two separate polypeptides that are coded for by two different genes. The two domain type GMP synthetases have been studied in some detail while the two subunit type GMPS has remained largely unexplored except for a single study on P. horikoshii GMPS. Current study investigates the mechanism of subunit association, catalysis and ammonia channeling in a two-subunit-type GMP synthetase from Methanocaldococcus jannaschii, a hyperthermophilc archaeon. Studies on the structural and functional aspects of GMPS synthetases from other organisms have also been discussed."