An application of protein engineering to determine the phase of crystal structure of Taq DNA polymerase

Abstract

Taq DNA polymerase from Thermus aquaticus is used in the polymerase chain reaction. Not only is Taq DNA polymerase highly valuable in the commercial market for the polymerase chain reaction but also important in studying DNA replication. In order to determine the crystal structure of Taq DNA polymerase, it was necessary to use heavy atom multiple isomorphous replacement in addition to molecular replacement. The success of the multiple isomorphous replacement is often facilitated in a protein which has a reasonable number of cysteines; however, wild type Taw DNA polymerase has no cysteines. To provide binding sites for mercurys, three serines in Taq DNA polymerase were replaced by cysteines using site-directed mutagenesis. This allowed determination of the crystal structure of Taq DNA polymerase at 2.4 ? resolution by multiple isomorphous replacement.