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. Author manuscript; available in PMC: 2011 Sep 13.

Published in final edited form as: Nature. 2009 Sep 16;461(7264):621–626. doi: 10.1038/nature08357

(a) Mass spectra of tryptic N-terminal heptapeptides from Mtb proteasomes that were untreated (i), HT1171-treated (ii), treated with glutaraldehyde/Na(CN)BH₃ after trypsin digestion (iii), or treated with glutaraldehyde/Na(CN)BH₃ after HT1171 treatment and trypsin digestion (iv). All ions were confirmed by MS/MS analysis (Fig. S7a–d). Reaction equations illustrate proposed modification of active site Thr1 by oxathiazol-2-one (i ii), and modification of primary amino groups at Thr1 and Lys7 with glutaraldehyde and Na(CN)BH₃ (i iii and ii iv). (b) Proposed mechanism of proteasome inactivation by oxathiazol-2-one. Paths marked by a, b, d lead to irreversible inhibition. In paths marked by c, hydrolysis of the inhibitor-enzyme intermediate allows the proteasome to degrade the oxathiazol-2-one without losing activity.

Inline graphic — (a) Mass spectra of tryptic N-terminal heptapeptides from Mtb proteasomes that were untreated (i), HT1171-treated (ii), treated with glutaraldehyde/Na(CN)BH₃ after trypsin digestion (iii), or treated with glutaraldehyde/Na(CN)BH₃ after HT1171 treatment and trypsin digestion (iv). All ions were confirmed by MS/MS analysis (Fig. S7a–d). Reaction equations illustrate proposed modification of active site Thr1 by oxathiazol-2-one (i ii), and modification of primary amino groups at Thr1 and Lys7 with glutaraldehyde and Na(CN)BH₃ (i iii and ii iv). (b) Proposed mechanism of proteasome inactivation by oxathiazol-2-one. Paths marked by a, b, d lead to irreversible inhibition. In paths marked by c, hydrolysis of the inhibitor-enzyme intermediate allows the proteasome to degrade the oxathiazol-2-one without losing activity.