How the MccB bacterial ancestor of ubiquitin E1 initiates biosynthesis of the microcin C7 antibiotic |
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Authors: | Catherine A Regni Rebecca F Roush Darcie J Miller Amanda Nourse Christopher T Walsh Brenda A Schulman |
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Affiliation: | 1. Department of Structural Biology, St Jude Children's Research Hospital, Memphis, TN, USA;2. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA;3. Hartwell Center for Bioinformatics and Biotechnology, St Jude Children's Research Hospital, Memphis, TN, USA;4. Howard Hughes Medical Institute |
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Abstract: | The 39‐kDa Escherichia coli enzyme MccB catalyses a remarkable posttranslational modification of the MccA heptapeptide during the biosynthesis of microcin C7 (MccC7), a ‘Trojan horse’ antibiotic. The approximately 260‐residue C‐terminal region of MccB is homologous to ubiquitin‐like protein (UBL) activating enzyme (E1) adenylation domains. Accordingly, MccB‐catalysed C‐terminal MccA‐acyl‐adenylation is reminiscent of the E1‐catalysed activation reaction. However, unlike E1 substrates, which are UBLs with a C‐terminal di‐glycine sequence, MccB's substrate, MccA, is a short peptide with an essential C‐terminal Asn. Furthermore, after an intramolecular rearrangement of MccA‐acyl‐adenylate, MccB catalyses a second, unique reaction, producing a stable phosphoramidate‐linked analogue of acyl‐adenylated aspartic acid. We report six‐crystal structures of MccB in apo, substrate‐, intermediate‐, and inhibitor‐bound forms. Structural and kinetic analyses reveal a novel‐peptide clamping mechanism for MccB binding to heptapeptide substrates and a dynamic‐active site for catalysing dual adenosine triphosphate‐consuming reactions. The results provide insight into how a distinctive member of the E1 superfamily carries out two‐step activation for generating the peptidyl‐antibiotic MccC7. |
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Keywords: | antibiotic MccB MccC7 microcin ubiquitin activating enzyme |
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