Defenbaugh DA, Nakai H. A context-dependent ClpX recognition determinant located at the C terminus of phage Mu repressor.
J Biol Chem 2003;
278:52333-9. [PMID:
14559921 DOI:
10.1074/jbc.m308724200]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The bacteriophage Mu immunity repressor is a conformationally sensitive sensor that can be interconverted between forms resistant to and sensitive to degradation by ClpXP protease. Protease-sensitive repressor molecules with an altered C-terminal sequence promote rapid degradation of the wild-type repressor by inducing its C-terminal end to become exposed. Here we determined that the last 5 C-terminal residues (CTD5) of the wild-type repressor contain the motif required for recognition by the ClpX molecular chaperone, a motif that is strongly dependent upon the context in which it is presented. Although attachment of the 11-residue ssrA degradation tag to the C terminus of green fluorescent protein (GFP) promoted its rapid degradation by ClpXP, attachment of 5-27 C-terminal residues of the repressor failed to promote degradation. Disordered peptides derived from 41 and 35 C-terminal residues of CcdA (CcdA41) and thioredoxin (TrxA35), respectively, activated CTD5 when placed as linkers between GFP and repressor C-terminal sequences. However, when the entire thioredoxin sequence was included as a linker to promote an ordered configuration of the TrxA35 peptide, the resulting substrate was not degraded. In addition, a hybrid tag, in which CTD5 replaced the 3-residue recognition motif of the ssrA tag, was inactive when attached directly to GFP but active when attached through the CcdA41 peptide. Thus, CTD5 is sufficient to act as a recognition motif but has requirements for its presentation not shared by the ssrA tag. We suggest that activation of CTD5 may require presentation on a disordered or flexible domain that confers ligand flexibility.
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