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Puromycin‐sensitive aminopeptidase is the major peptidase responsible for digesting polyglutamine sequences released by proteasomes during protein degradation
Author(s) -
Bhutani N,
Venkatraman P,
Goldberg A L
Publication year - 2007
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/sj.emboj.7601592
Subject(s) - biology , puromycin , aminopeptidase , proteasome , biochemistry , protein degradation , degradation (telecommunications) , microbiology and biotechnology , amino acid , protein biosynthesis , leucine , telecommunications , computer science
Long stretches of glutamine (Q) residues are found in many cellular proteins. Expansion of these polyglutamine (polyQ) sequences is the underlying cause of several neurodegenerative diseases (e.g. Huntington's disease). Eukaryotic proteasomes have been found to digest polyQ sequences in proteins very slowly, or not at all, and to release such potentially toxic sequences for degradation by other peptidases. To identify these key peptidases, we investigated the degradation in cell extracts of model Q‐rich fluorescent substrates and peptides containing 10–30 Q's. Their degradation at neutral pH was due to a single aminopeptidase, the puromycin‐sensitive aminopeptidase (PSA, cytosol alanyl aminopeptidase). No other known cytosolic aminopeptidase or endopeptidase was found to digest these polyQ peptides. Although tripeptidyl peptidase II (TPPII) exhibited limited activity, studies with specific inhibitors, pure enzymes and extracts of cells treated with siRNA for TPPII or PSA showed PSA to be the rate‐limiting activity against polyQ peptides up to 30 residues long. (PSA digests such Q sequences, shorter ones and typical (non‐repeating) peptides at similar rates.) Thus, PSA, which is induced in neurons expressing mutant huntingtin, appears critical in preventing the accumulation of polyQ peptides in normal cells, and its activity may influence susceptibility to polyQ diseases.