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SmiA is a hybrid priming/scaffolding adaptor for the LonA protease in Bacillus subtilis.

ABSTRACT: Regulatory proteolysis targets properly folded clients via a combination of cis-encoded degron sequences and trans-expressed specificity factors called adaptors. SmiA of Bacillus subtilis was identified as the first adaptor protein for the Lon family of proteases, but the mechanism of SmiA-dependent proteolysis is unknown. Here, we develop a fluorescence-based assay to measure the kinetics of SmiA-dependent degradation of its client SwrA and show that SmiA-SwrA interaction and the SwrA degron were both necessary, but not sufficient, for proteolysis. Consistent with a scaffolding adaptor mechanism, we found that stoichiometric excess of SmiA caused substrate-independent inhibition of LonA-dependent turnover. Furthermore, SmiA was strictly required even when SwrA levels were high suggesting that a local increase in substrate concentration mediated by the scaffold was not sufficient for proteolysis. Moreover, SmiA function could not be substituted by thermal denaturation of the substrate, consistent with a priming adaptor mechanism. Taken together, we conclude that SmiA functions via a mechanism that is a hybrid between scaffolding and priming models.

SUBMITTER: Olney SG

PROVIDER: S-EPMC9204741 | biostudies-literature |

REPOSITORIES: biostudies-literature

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The C-Terminal Region of Bacillus subtilis SwrA Is Required for Activity and Adaptor-Dependent LonA Proteolysis.

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