Proteolytic assays reveal that human HSP90β is a substrate of CD2830.
A, Caco-2 whole cell lysates analyzed via SDS-PAGE before (−) and after (+) incubation with rCD2830. Arrow points at cleavage product. B, recombinant human HSP90β analyzed via SDS-PAGE after incubation with rCD2830 for different time periods. C, SDS-PAGE analysis of human HSP90α after 20 h of incubation with (+) or without (−) rCD2830. D, LC–ion trap MS(/MS) analysis of tryptic digests of HSP90β before and after cleavage with rCD2830. A specific semi-tryptic peptide of HSP90β was identified only in the run from the CD2830-cleaved HSP90β. MS/MS analysis of this peptide demonstrated that HSP90β was cleaved by CD2830 after Ala-702 (see F). E, Electrospray ionization Q-TOF-MS analysis of the C-terminally released HSP90β peptide after cleavage by rCD2830. F, identification of the rCD2830 cleavage site in human HSP90β and alignment of the C-terminal amino acid sequences of human HSP90β and HSP90α. Arrowhead indicates the CD2830 cleavage site between Ala-702 and Ala-703 of human HSP90β. MW, molecular weight in kilodaltons.