title: Heterologous expression studies of Saccharomyces cerevisiae reveal two distinct trypanosomatid CaaX protease activities and identify their potential targets.
abstract: The CaaX tetrapeptide motif typically directs three sequential posttranslational modifications, namely, isoprenylation, proteolysis, and carboxyl methylation. In all eukaryotic systems evaluated to date, two CaaX proteases (Rce1 and Ste24/Afc1) have been identified. Although the Trypanosoma brucei genome also encodes two putative CaaX proteases, the lack of detectable T. brucei Ste24 activity in trypanosome cell extracts has suggested that CaaX proteolytic activity within this organism is solely attributed to T. brucei Rce1 (J. R. Gillespie et al., Mol. Biochem. Parasitol. 153:115-124. 2007). In this study, we demonstrate that both T. brucei Rce1 and T. brucei Ste24 are enzymatically active when heterologously expressed in yeast. Using a-factor and GTPase reporters, we demonstrate that T. brucei Rce1 and T. brucei Ste24 possess partially overlapping specificities much like, but not identical to, their fungal and human counterparts. Of interest, a CaaX motif found on a trypanosomal Hsp40 protein was not cleaved by either T. brucei CaaX protease when examined in the context of the yeast a-factor reporter but was cleaved by both in the context of the Hsp40 protein itself when evaluated using an in vitro radiolabeling assay. We further demonstrate that T. brucei Rce1 is sensitive to small molecules previously identified as inhibitors of the yeast and human CaaX proteases and that a subset of these compounds disrupt T. brucei Rce1-dependent localization of our GTPase reporter in yeast. Together, our results suggest the conserved presence of two CaaX proteases in trypanosomatids, identify an Hsp40 protein as a substrate of both T. brucei CaaX proteases, support the potential use of small molecule CaaX protease inhibitors as tools for cell biological studies on the trafficking of CaaX proteins, and provide evidence that protein context influences T. brucei CaaX protease specificity.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Georgia, 120 Green Street, Athens, GA 30602, USA.
authors.forename: David Z
authors.initials: DZ
authors.lastname: Mokry
authors.forename: Surya P
authors.initials: SP
authors.lastname: Manandhar
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Chicola
authors.forename: George M
authors.initials: GM
authors.lastname: Santangelo
authors.forename: Walter K
authors.initials: WK
authors.lastname: Schmidt
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004252:DNA Mutational Analysis; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D049770:Genes, Mating Type, Fungal; D049452:Green Fluorescent Proteins / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D020128:Inhibitory Concentration 50; D010641:Phenotype; D011480:Protease Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D015800:Protozoan Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013379:Substrate Specificity / Q000187:drug effects; D013696:Temperature; D014346:Trypanosoma brucei brucei / Q000187:drug effects / Q000201:enzymology*
chemical_list: D050956:HSP40 Heat-Shock Proteins; D011480:Protease Inhibitors; D015800:Protozoan Proteins; D029701:Saccharomyces cerevisiae Proteins; C070319:YDJ1 protein, S cerevisiae; D049452:Green Fluorescent Proteins; D010450:Endopeptidases; D020558:GTP Phosphohydrolases