| Title: | Proteolytic processing of certain CaaX motifs can occur in the absence of the Rce1p and Ste24p CaaX proteases |
| Author(s): | Krishnankutty RK; Kukday SS; Castleberry AJ; Breevoort SR; Schmidt WK; |
| Address: | "Department of Biochemistry and Molecular Biology, University of Georgia, Athens, 30602, USA" |
| ISSN/ISBN: | 1097-0061 (Electronic) 0749-503X (Print) 0749-503X (Linking) |
| Abstract: | "The CaaX motif directs C-terminal protein modifications that include isoprenylation, proteolysis and carboxylmethylation. Proteolysis is generally believed to require either Rce1p or Ste24p. While investigating the substrate specificity of these proteases, using the yeast a-factor mating pheromone as a reporter, we observed Rce1p- and Ste24p-independent mating (RSM) when the CKQQ CaaX motif was used in lieu of the natural a-factor CVIA motif. Uncharged or negatively charged amino acid substitutions at the a(1) position of the CKQQ motif prevented RSM. Alanine substitutions at the a(2) and X positions enhanced RSM. Random mutagenesis of the CaaX motif provided evidence that RSM occurs with approximately 1% of all possible CaaX motif permutations. Combined mutational and genetic data indicate that RSM-promoting motifs have a positively charged amino acid at the a(1) position. Two of nine naturally occurring yeast CaaX motifs conforming to this pattern promoted RSM. The activity of the isoprenylcysteine carboxyl methyltransferase Ste14p was required for RSM, indicating that RSM-promoting CaaX motifs are indeed proteolysed. RSM was enhanced by the overexpression of Axl1p or Ste23p, suggesting a role for these M16A subfamily metalloproteases in this process. We have also determined that an N-terminal extension of the a-factor precursor, which is typically removed by the yeast M16A enzymes, is required for optimal RSM. These observations suggest a model that involves targeting of the a-factor precursor to the peptidosome cavity of M16A enzymes where subsequent interactions between RSM-promoting CaaX motifs and the active site of the M16A enzyme lead to proteolytic cleavage" |
| Keywords: | "Amino Acid Motifs DNA Mutational Analysis Genes, Reporter Mating Factor Membrane Proteins/genetics/*metabolism Metalloendopeptidases/genetics/*metabolism Models, Biological Mutagenesis Peptides/genetics/metabolism Proprotein Convertases/genetics/*metaboli;" |
| Notes: | "MedlineKrishnankutty, Ranjith K Kukday, Sayali S Castleberry, Amanda J Breevoort, Sarah R Schmidt, Walter K eng R01 GM067092/GM/NIGMS NIH HHS/ R01 GM67092/GM/NIGMS NIH HHS/ Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't England 2009/06/09 Yeast. 2009 Aug; 26(8):451-63. doi: 10.1002/yea.1678" |
