Scapin G, Ozturk D H, Grubmeyer C, Sacchettini J C
Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Biochemistry. 1995 Aug 29;34(34):10744-54. doi: 10.1021/bi00034a006.
The three-dimensional structure of Salmonella typhimurium orotate phosphoribosyltransferase (OPRTase) in complex with the ribose 5-phosphate donor alpha-D-5--phosphoribosyl-1-pyrophosphate (PRPP) and the nitrogenous base orotic acid has been solved and refined with X-ray diffraction data extending to 2.3 A resolution to a crystallographic R-factor of 18.7%. The complex was generated by carrying out catalysis in the crystal. Comparison of this structure with the previously reported structure of the orotidine 5'-monophosphate (OMP) complex [Scapin, G., Grubmeyer, C., and Sacchettini, J. C. (1994) Biochemistry 33, 1287-1294] revealed that the enzyme backbone undergoes only small movements. The most significant differences occur near the active site, at Ala71-Gly74, with the largest difference involving the side chains of Lys73, Val127-Ala133, the 5'-phosphate binding loop, and a long, solvent-exposed loop at the dimer interface. The position of the ribose moiety is, on the other hand, very different in the OMP and PRPP.orotate complexes, with its anomeric carbon moving approximately 7 A across the binding cavity. In the PRPP.orotate complex the highly conserved acidic side chain of Asp124 interacts with the ribose of PRPP, whereas there are no interactions of this aspartate with the substrate in the OMP complex.
鼠伤寒沙门氏菌乳清酸磷酸核糖转移酶（OPRTase）与核糖5-磷酸供体α-D-5'-磷酸核糖-1-焦磷酸（PRPP）及含氮碱基乳清酸形成的复合物的三维结构已通过X射线衍射数据解析并精修，该数据延伸至2.3 Å分辨率，晶体学R因子为18.7%。该复合物是通过在晶体中进行催化生成的。将此结构与先前报道的5'-磷酸乳清苷（OMP）复合物的结构[斯卡平，G.，格鲁布迈尔，C.，和萨凯蒂尼，J. C.（1994年）《生物化学》33，1287 - 1294]进行比较，发现酶的主链仅发生了微小移动。最显著的差异出现在活性位点附近，即Ala71 - Gly74处，最大的差异涉及Lys73、Val127 - Ala133的侧链、5'-磷酸结合环以及二聚体界面处一个长的、暴露于溶剂中的环。另一方面，核糖部分在OMP和PRPP - 乳清酸复合物中的位置差异很大，其异头碳在结合腔内移动了约7 Å。在PRPP - 乳清酸复合物中，Asp124高度保守的酸性侧链与PRPP的核糖相互作用，而在OMP复合物中该天冬氨酸与底物没有相互作用。
