title: Changing the net charge from negative to positive makes ribonuclease Sa cytotoxic.
abstract: Ribonuclease Sa (pI = 3.5) from Streptomyces aureofaciens and its 3K (D1K, D17K, E41K) (pI = 6.4) and 5K (3K + D25K, E74K) (pI = 10.2) mutants were tested for cytotoxicity. The 5K mutant was cytotoxic to normal and v-ras-transformed NIH3T3 mouse fibroblasts, but RNase Sa and 3K were not. The structure, stability, and activity of the three proteins are comparable, but the net charge at pH 7 increases from -7 for RNase Sa to -1 for 3K and to +3 for 5K. These results suggest that a net positive charge is a key determinant of ribonuclease cytotoxicity. The cytotoxic 5K mutant preferentially attacks v-ras-NIH3T3 fibroblasts, suggesting that mammalian cells expressing the ras-oncogene are potential targets for ribonuclease-based drugs.
authors.affiliation: Department of Microbiology, Kazan State University, 420008 Kazan, Russia.
authors.forename: Olga N
authors.initials: ON
authors.lastname: Ilinskaya
authors.forename: Florian
authors.initials: F
authors.lastname: Dreyer
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Mitkevich
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Shaw
authors.forename: C Nick
authors.initials: CN
authors.lastname: Pace
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Makarov
mesh_terms: D016475:3T3 Cells; D000818:Animals; D005347:Fibroblasts; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D051379:Mice; D009154:Mutation; D012260:Ribonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D013304:Streptomyces aureofaciens / Q000201:enzymology; D013329:Structure-Activity Relationship
chemical_list: D007527:Isoenzymes; D012260:Ribonucleases; C077002:ribonuclease Sa3