The Arabidopsis AtSTE24 is a CAAX protease with broad substrate specificity.
Following prenylation, the proteins are subject to two prenyl-dependent modifications at their C-terminal end, which are required for their subcellular targeting. First, the three C-terminal residues of the CAAX box prenylation signaling motif are removed, which is followed by methylation of the free carboxyl group of the prenyl cysteine moiety. An Arabidopsis homologue of the yeast CAAX protease STE24 (AFC1) was cloned and expressed in rce1 Delta ste24 Delta mutant yeast to demonstrate functional complementation. The petunia calmodulin CaM53 is a prenylated protein terminating in a CTIL CAAX box. Coupled methylation proteolysis assays demonstrated the processing of CaM53 by AtSTE24. In addition, AtSTE24 promoted plasma membrane association of the GFP-Rac fusion protein, which terminates with a CLLM CAAX box. Interestingly, a plant homologue of the second and major CAAX protease in yeast and animal cells, RCE1, was not identified despite the availability of vast amounts of sequence data. Taken together, these data suggest that AtSTE24 may process several prenylated proteins in plant cells, unlike its yeast homologue, which processes only a-mating factor, and its mammalian homologue, for which prenyl-CAAX substrates have not been established. Transient expression of GFPAtSTE24 in leaf epidermal cells of Nicotiana benthamiana showed that AtSTE24 is exclusively localized in the endoplasmic reticulum, suggesting that prenylated proteins in plants are first targeted to the endoplasmic reticulum following their prenylation.
Bracha
Keren
K
Department of Plant Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
Lavy
Meirav
M
Yalovsky
Shaul
S
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins; D001483:Base Sequence; D018076:DNA, Complementary; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017368:Protein Prenylation; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D008666:Metalloendopeptidases; C104079:STE24 protein, Arabidopsis