Substrate specificity of the oncoprotein v-Fps: site-specific mutagenesis of the putative P+1 pocket.
Based on the X-ray structure of the insulin receptor kinase [Hubbard, S. R. (1997) EMBO J. 16, 5572-5581], Arg-1130 in the oncoprotein v-Fps, a nonreceptor tyrosine protein kinase, is predicted to interact with the P+1 glutamate in substrate peptides. To determine whether this residue is an important recognition element in v-Fps, Arg-1130 was substituted with leucine (R1130L) and glutamic acid (R1130E). The ability of these mutants to phosphorylate the peptide EAEIYXAIE, where X is glutamic acid, alanine, or lysine, was assessed. A comparison of the rates of peptide phosphorylation under limiting substrate concentrations (i.e., k(cat)/K(m) conditions) indicates that substrate specificity is altered by the electrostatic environment of the P+1 pocket. When the pocket displays a positive charge (Arg-1130; wild type), no charge (R1130L), or a negative charge (R1130E), v-Fps prefers to phosphorylate the glutamate peptide over the lysine peptide by a 200:1, 9:1, or 1:1 margin. While k(cat)/K(m) for the glutamate peptide is 50-fold higher for wild type compared to R1130E, k(cat)/K(m) for the lysine peptide is 3-fold higher for R1130E compared to wild type, a 150-fold change in relative substrate specificity. Analysis of the individual steps in the kinetic mechanism using viscosometric techniques indicates that the wild-type enzyme binds the glutamate peptide 3-fold better than the alanine peptide and, at least, 10-fold better than the lysine peptide. For R1130L, this margin range is reduced substantially, and for R1130E, no binding preference is observed. Nonetheless, the lysine peptide binds, at least, 4-fold better to R1130E than to wild type, and the glutamate peptide binds 3-fold poorer to R1130E than to wild type. The mutants lower the phosphoryl transfer rate by 4-30-fold for the three peptides, suggesting that Arg-1130 helps to position the tyrosine for optimum catalysis. The data indicate that a single mutation in v-Fps can alter significantly the relative substrate specificity by about 2 orders of magnitude with, at least, 50% of this effect occurring through relative changes in peptide binding affinity.
Konkol
L
L
Department of Pharmacology, University of California, San Diego, La Jolla 92093-0506, USA.
Hirai
T J
TJ
Adams
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D015681:Fusion Proteins, gag-onc / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity / Q000235:genetics; D014783:Viscosity
D015681:Fusion Proteins, gag-onc; D010455:Peptides; D011994:Recombinant Proteins; D011505:Protein-Tyrosine Kinases; C068415:v-fps oncogene protein, Fujinami sarcoma virus