Peptide specificity of protein prenyltransferases is determined mainly by reactivity rather than binding affinity.
Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase I) catalyze the attachment of lipid groups from farnesyl diphosphate and geranylgeranyl diphosphate, respectively, to a cysteine near the C-terminus of protein substrates. FTase and GGTase I modify several important signaling and regulatory proteins with C-terminal CaaX sequences ("C" refers to the cysteine residue that becomes prenylated, "a" refers to any aliphatic amino acid, and "X" refers to any amino acid). In the CaaX paradigm, the C-terminal X-residue of the protein/peptide confers specificity for FTase or GGTase I. However, some proteins, such as K-Ras, RhoB, and TC21, are substrates for both FTase and GGTase I. Here we demonstrate that the C-terminal amino acid affects the binding affinity of K-Ras4B-derived hexapeptides (TKCVIX) to FTase and GGTase I modestly. In contrast, reactivity, as indicated by transient and steady-state kinetics, varies significantly and correlates with hydrophobicity, volume, and structure of the C-terminal amino acid. The reactivity of FTase decreases as the hydrophobicity of the C-terminal amino acid increases whereas the reactivity of GGTase I increases with the hydrophobicity of the X-group. Therefore, the hydrophobicity, as well as the structure of the X-group, determines whether peptides are specific for farnesylation, geranylgeranylation, or dual prenylation.
Hartman
Heather L
HL
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Hicks
Katherine A
KA
Fierke
Carol A
CA
D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D007700:Kinetics; D009842:Oligopeptides / Q000378:metabolism; D017368:Protein Prenylation; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D013379:Substrate Specificity; D018631:ras Proteins / Q000378:metabolism
C117307:KRAS protein, human; D009842:Oligopeptides; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; C064911:p21(ras) farnesyl-protein transferase; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins