title: Compensating effects on the cytotoxicity of ribonuclease A variants.
abstract: Ribonuclease (RNase) A can be endowed with cytotoxic activity by enabling it to evade the cytosolic ribonuclease inhibitor protein (RI). Enhancing its conformational stability can increase further its cytotoxicity. Herein, the A4C/K41R/G88R/V118C variant of RNase A was created to integrate four individual changes that greatly decrease RI affinity (K41R/G88R) and increase conformational stability (A4C/V118C). Yet, the variant suffers a decrease in ribonucleolytic activity and is only as potent a cytotoxin as its precursors. Thus, individual changes that increase cytotoxicity can have offsetting consequences. Overall, cytotoxicity correlates well with the maintenance of ribonucleolytic activity in the presence of RI. The parameter (k(cat)/K(m))(cyto), which reports on the ability of a ribonuclease to manifest its ribonucleolytic activity in the cytosol, is especially useful in predicting the cytotoxicity of an RNase A variant.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706-1569, USA.
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Dickson
authors.forename: Caroline L
authors.initials: CL
authors.lastname: Dahlberg
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Raines
mesh_terms: D004789:Enzyme Activation; D004795:Enzyme Stability; D006801:Humans; D020014:K562 Cells / Q000187:drug effects* / Q000378:metabolism; D011487:Protein Conformation; D015202:Protein Engineering / Q000379:methods*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000633:toxicity; D012259:Ribonuclease, Pancreatic / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000633:toxicity*; D013223:Statistics as Topic; D013329:Structure-Activity Relationship; D013936:Thymidine / Q000493:pharmacokinetics
chemical_list: D011994:Recombinant Proteins; D012259:Ribonuclease, Pancreatic; D013936:Thymidine