Crystallographic analyses of hyperthermophilic proteins.

Following the first structure determination in 1992 of a protein from a hyperthermophilic organism, the rubredoxin from Pyrococcus furiosus, structures of hyperthermophilic proteins have appeared at an ever increasing rate, with more than 50 distinct structures having been submitted to the Protein Data Bank as of October 1999 (Table I). These structure determinations have been undertaken for many of the reasons discussed elsewhere in this volume-to understand the structural basis of thermostability; to more fully characterize proteins with unusual cofactors or active centers; for biotechnological purposes; as homologs of eukaryotic proteins, especially those involved in some aspect of macromolecular biosynthesis; and as part of structural genomics efforts, because they either do, or do not, look like some other proteins. As there is an expectation that hyperthermostable proteins should be more robust and potentially better suited for withstanding the solution conditions and time scales of crystallization experiments, these proteins have provided attractive targets for structural studies. The focus of this chapter is to review the status and some general implications of crystallographic studies on hyperthermophilic proteins, with emphasis on relevant technical aspects of the structure determination, quality of the crystals, and conclusions about thermal stability and other properties of these fascinating proteins.