Purification, crystallization and preliminary X-ray diffraction studies of the soluble domain of the oligosaccharyltransferase STT3 subunit from the thermophilic archaeon Pyrococcus furiosus.

Oligosaccharyltransferase catalyzes the transfer of preassembled oligosaccharides onto asparagine residues in nascent polypeptide chains. The STT3 subunit is thought to bear the catalytic site. The C-terminal domain of the STT3 protein of Pyrococcus furiosus was expressed in Escherichia coli cells. STT3 protein prepared from two different sources, the soluble fraction and the inclusion bodies, produced crystals that diffracted to 2.7 A. During crystallization screening, cocrystals of P. furiosus STT3 with an E. coli 50S ribosomal protein, L7/L12, were accidentally obtained. This cross-species interaction is not biologically relevant, but may be used to design a built-in polypeptide substrate for the STT3 crystals.