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First published online May 20, 2005; 10.1104/pp.104.057406 Plant Physiology 138:1046-1057 (2005) © 2005 American Society of Plant Biologists Tripeptidyl Peptidase II. An Oligomeric Protease Complex from Arabidopsis1Department of Genetics (A.J.B., P.Y., R.D.V.) and Department of Chemistry (M.S., L.M.S.), University of Wisconsin, Madison, Wisconsin 53706
The breakdown of most nuclear and cytoplasmic proteins involves their partial cleavage by the 26S proteasome followed by further disassembly to free amino acids by the combined action of endo- and exopeptidases. In animals, one important intermediate exopeptidase is tripeptidyl peptidase (TPP)II, which digests peptide products of the 26S proteasome and other endopeptidases into tripeptides. Here, we describe the purification and characterization of TPPII from Arabidopsis (Arabidopsis thaliana). Like its animal counterparts, Arabidopsis TPPII exists as a soluble, approximately 5- to 9-MD complex. Two related species of 153 and 142 kD are present in the purified preparations that are derived from a single TPP2 gene. Sequencing by Edman degradation of the intact polypeptides and mass spectrometry of proteolytic fragments demonstrated that the 142-kD form mainly differs from the 153-kD form by a truncation at the C-terminal end. This serine protease is a member of the subtilisin superfamily and is sensitive to the inhibitors alanine-alanine-phenylalanine-chloromethylketone and butabindide, which are diagnostic for the TPPII subfamily. The Arabidopsis TPP2 gene is widely expressed in many tissue types with related genes evident in other plant genomes. Whereas the 26S proteasome is essential, TPPII appears not as important for plant physiology. An Arabidopsis T-DNA mutant defective in TPP2 expression displays no phenotypic abnormalities and is not hypersensitive to either amino acid analogs or the 26S proteasome inhibitor MG132. As a consequence, plants likely contain other intermediate exopeptidases that assist in amino acid recycling.
1 This work was supported by the National Science Foundation Arabidopsis 2010 Initiative (grant no. MCB–0115870), by the U.S. Department of Energy Basic Energy Sciences program (grant no. DE–FG02–88ER13968 to R.D.V.), by the National Heart, Lung and Blood Institute-National Institutes of Health (grant no. N01–HV–28182 to L.M.S.), and by a Louis and Elsa Thomsen Wisconsin Distinguished Predoctoral Fellowship (to P.Y.). 2 These authors contributed equally to the paper. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.057406. * Corresponding author; e-mail vierstra{at}wisc.edu; fax 608–262–2976. Received November 30, 2004; returned for revision January 25, 2005; accepted February 3, 2005. This article has been cited by other articles:
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