title: X-ray structure of two crystalline forms of a streptomycete ribonuclease with cytotoxic activity.
abstract: Ribonuclease (RNase) Sa3 is secreted by the Gram-positive bacterium Streptomyces aureofaciens. The enzyme catalyzes the cleavage of RNA on the 3' side of guanosine residues. Here, x-ray diffraction analysis was used to determine the three-dimensional structure of two distinct crystalline forms of RNase Sa3 to a resolution of 2.0 and 1.7 A. These two structures are similar to each other as well as to that of a homolog, RNase Sa. All of the key active-site residues of RNase Sa (Asn(42), Glu(44), Glu(57), Arg(72), and His(88)) are located in the putative active site of RNase Sa3. Also herein, RNase Sa3 is shown to be toxic to human erythroleukemia cells in culture. Like onconase, which is an amphibian ribonuclease in Phase III clinical trials as a cancer chemotherapeutic, RNase Sa3 is not inhibited by the cytosolic ribonuclease inhibitor protein. Thus, a prokaryotic ribonuclease can be toxic to mammalian cells.
authors.affiliation: Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 84251 Bratislava, Slovak Republic. umbisevc@savba.sk
authors.forename: Jozef
authors.initials: J
authors.lastname: Sevcik
authors.forename: Lubica
authors.initials: L
authors.lastname: Urbanikova
authors.forename: Peter A
authors.initials: PA
authors.lastname: Leland
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Raines
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D001216:Asparagine / Q000737:chemistry; D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D005973:Glutamine / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry*; D020014:K562 Cells; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012260:Ribonucleases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D013304:Streptomyces aureofaciens / Q000201:enzymology*; D013696:Temperature; D014407:Tumor Cells, Cultured; D014961:X-Ray Diffraction
chemical_list: D007527:Isoenzymes; D005973:Glutamine; D006639:Histidine; D001216:Asparagine; D001120:Arginine; D012260:Ribonucleases; C077002:ribonuclease Sa3