title: Active site-directed inhibitors of Rhodococcus 20 S proteasome. Kinetics and mechanism.
abstract: We have studied the mechanism of inhibition of the recombinant Rhodococcus proteasome by four different chemical classes of active site-directed small molecule inhibitors. Clasto-lactacystin beta-lactone is a time-dependent inhibitor of the Rhodococcus proteasome's ability to hydrolyze Suc-Leu-Leu-Val-Tyr-AMC, a substrate for this proteasome's single type of active site, and proceeds with a kinact/[I] of 1,700 M-1 s-1. Using peptide mapping of tryptic digests, LC/MS, and amino acid sequence analysis, we have established that the Ogamma of the hydroxyl group on the N-terminal threonine of the beta-subunit is the sole modification made by the beta-lactone. Active site titrations of the Rhodococcus proteasome with reversible peptide aldehydes show the expected stoichiometry of one inhibitor molecule per beta-subunit. Prior modification with beta-lactone completely abrogates the binding of peptidyl boronic acid inhibitors, suggesting that these inhibitors also inactivate the enzyme by reacting with the Ogamma moiety on Thr1. High performance liquid chromatography analysis of peptidyl vinyl sulfone-modified intact Rhodococcus proteasome beta-subunit and its tryptic peptides suggests that the peptidyl vinyl sulfone modifies a residue in the N-terminal 20 amino acids. This modification is also blocked by prior treatment with beta-lactone.
authors.affiliation: ProScript Inc., Cambridge, Massachusetts 02139, USA.
authors.forename: T
authors.initials: T
authors.lastname: Mc Cormack
authors.forename: W
authors.initials: W
authors.lastname: Baumeister
authors.forename: L
authors.initials: L
authors.lastname: Grenier
authors.forename: C
authors.initials: C
authors.lastname: Moomaw
authors.forename: L
authors.initials: L
authors.lastname: Plamondon
authors.forename: B
authors.initials: B
authors.lastname: Pramanik
authors.forename: C
authors.initials: C
authors.lastname: Slaughter
authors.forename: F
authors.initials: F
authors.lastname: Soucy
authors.forename: R
authors.initials: R
authors.lastname: Stein
authors.forename: F
authors.initials: F
authors.lastname: Zühl
authors.forename: L
authors.initials: L
authors.lastname: Dick
mesh_terms: D001665:Binding Sites; D003546:Cysteine Endopeptidases / Q000187:drug effects*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D007700:Kinetics; D007783:Lactones / Q000494:pharmacology*; D009097:Multienzyme Complexes / Q000187:drug effects*; D046988:Proteasome Endopeptidase Complex; D011994:Recombinant Proteins / Q000187:drug effects; D012240:Rhodococcus / Q000201:enzymology*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007783:Lactones; D009097:Multienzyme Complexes; D011994:Recombinant Proteins; C098869:clasto-lactacystin beta-lactone; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex