Atomic resolution data reveal flexibility in the structure of RNase Sa.
Ribonuclease from Streptomyces aureofaciens, the bacterial source for the industrial production of chlorotetracycline, is a guanylate endoribonuclease (RNase Sa; EC 3.1.27.3) which hydrolyses the phosphodiester bonds of single-stranded RNA at the 3'-side of guanosine nucleotides with high specificity. The structure of the enzyme was previously refined at atomic resolution (1.2 A) using room-temperature data. Here, the RNase Sa structure refined against 1.0 A data collected at cryogenic temperature is reported. There are two surface loops in molecule A and one in molecule B for which two main-chain conformations are modelled: these loops contain active-site residues. The separation for most of the corresponding main-chain atoms in the two conformations is about 0.8 A, with a maximum of 2.5 A. The two regions of dual conformation represent the most important differences in comparison with the structure determined at room temperature, where the corresponding loops have one conformation only but the largest degree of anisotropy. The flexibility of the loops observed in the structure of RNase Sa is directly linked to the need for the active site to interact productively with substrates and/or inhibitors.
Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovak Republic. umbisevc@savba.savba.sk
Jozef
J
Sevcík
Victor S
VS
Lamzin
Zbigniew
Z
Dauter
Keith S
KS
Wilson
D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006157:Guanosine Monophosphate / Q000737:chemistry; D007527:Isoenzymes / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011487:Protein Conformation; D012260:Ribonucleases / Q000737:chemistry*; D055672:Static Electricity; D013304:Streptomyces aureofaciens / Q000201:enzymology; D013696:Temperature
D007527:Isoenzymes; C068152:3'-guanylic acid; D006157:Guanosine Monophosphate; D012260:Ribonucleases; C077002:ribonuclease Sa3