Recognition of RNase Sa by the inhibitor barstar: structure of the complex at 1.7 A resolution.
We report the 1.7 A resolution structure of RNase Sa complexed with the polypeptide inhibitor barstar. The crystals are in the hexagonal space group P65 with unit-cell dimensions a = b = 56.9, c = 135.8 A and the asymmetric unit contains one molecule of the complex. RNase Sa is an extracellular microbial ribonuclease produced by Streptomyces aureofaciens. Barstar is the natural inhibitor of barnase, the ribonuclease of Bacillus amyloliquefaciens. It inhibits RNase Sa and barnase in a similar manner by steric blocking of the active site. The structure of RNase Sa is very similar to that observed in crystals of the native enzyme and its complexes with nucleotides. Barstar retains the structure found in its complex with barnase. The accessible surface area of protein buried in the complex is about 300 A2 smaller and there are fewer hydrogen bonds in the enzyme-inhibitor interface in RNase Sa-barstar than in barnase-barstar, providing an explanation of the reduced binding affinity in the former. Previous studies of barstar complexes have used mutants of the inhibitor and this is the first structure which includes wild-type barstar.
Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 84251 Bratislava, Slovak Republic.
J
J
Sevcík
L
L
Urbanikova
Z
Z
Dauter
K S
KS
Wilson
D000595:Amino Acid Sequence; D001407:Bacillus / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D007527:Isoenzymes / Q000737:chemistry* / Q000378:metabolism; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012260:Ribonucleases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D046911:Macromolecular Substances; C057438:barstar protein, Bacillus amyloliquefaciens; D012260:Ribonucleases; C077002:ribonuclease Sa3; C019760:Bacillus amyloliquefaciens ribonuclease