Structural Basis of an N-Degron Adaptor with More Stringent Specificity.
Publication Type:
Journal ArticleSource:
Structure, Volume 24, Issue 2, p.232-42 (2016)Keywords:
Agrobacterium tumefaciens, Amino Acids, Bacterial Proteins, Carrier Proteins, Crystallography, X-Ray, Gene Expression Regulation, Bacterial, Models, Molecular, Mutagenesis, Site-Directed, Peptide Hydrolases, Protein Conformation, Protein Unfolding, Substrate SpecificityAbstract:
<p>The N-end rule dictates that a protein's N-terminal residue determines its half-life. In bacteria, the ClpS adaptor mediates N-end-rule degradation, by recognizing proteins bearing specific N-terminal residues and delivering them to the ClpAP AAA+ protease. Unlike most bacterial clades, many α-proteobacteria encode two ClpS paralogs, ClpS1 and ClpS2. Here, we demonstrate that both ClpS1 and ClpS2 from A. tumefaciens deliver N-end-rule substrates to ClpA, but ClpS2 has more stringent binding specificity, recognizing only a subset of the canonical bacterial N-end-rule residues. The basis of this enhanced specificity is addressed by crystal structures of ClpS2, with and without ligand, and structure-guided mutagenesis, revealing protein conformational changes and remodeling in the substrate-binding pocket. We find that ClpS1 and ClpS2 are differentially expressed during growth in A. tumefaciens and conclude that the use of multiple ClpS paralogs allows fine-tuning of N-end-rule degradation at the level of substrate recognition.</p>