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Updated: May 15, 2026
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Residue-specific Incorporation of Noncanonical Amino Acids into Model Proteins Using an Escherichia coli Cell-free Transcription-translation System
Published on: August 1, 2016
Structural basis for C-ribosylation in the alnumycin A biosynthetic pathway
Terhi Oja1, Laila Niiranen, Tatyana Sandalova
1Department of Biochemistry and Food Chemistry, University of Turku, FIN-20014 Turku, Finland.
Summary
Researchers identified AlnA as a C-glycosynthase, catalyzing the attachment of D-ribose-5-phosphate to prealnumycin. AlnB then dephosphorylates the intermediate, revealing a novel pathway for natural product glycosylation.
Area of Science:
- Biochemistry
- Natural Product Biosynthesis
- Enzymology
Background:
- Alnumycin A is a unique aromatic polyketide featuring a C-C bonded dioxane moiety.
- Previous work identified D-ribose-5-phosphate as the dioxane precursor and AlnA/AlnB as key enzymes in C-ribosylation.
Purpose of the Study:
- To provide direct evidence for AlnA acting as a natural C-glycosynthase.
- To elucidate the mechanism of C-ribosylation and dephosphorylation in Alnumycin A biosynthesis.
- To determine the structures of key enzymes and intermediates.
Main Methods:
- X-ray crystallography of AlnA (trimeric) and AlnB (monomeric).
- Structure determination of the intermediate alnumycin P.
- Mutagenesis studies to probe enzyme mechanisms.
Main Results:
- AlnA directly catalyzes C(8)-C(1') bond formation between prealnumycin and D-ribose-5-phosphate.
- The crystal structure of AlnA revealed an α/β/α fold, with D-ribose-5-phosphate bound in an open-chain form.
- AlnB, a haloacid dehalogenase superfamily member, dephosphorylates the intermediate.
- Crystal structures provided insights into the catalytic mechanisms of both enzymes, suggesting a Michael-type addition for AlnA and highlighting key residues for AlnB activity.
Conclusions:
- AlnA functions as a natural C-glycosynthase, establishing a novel route for carbohydrate attachment to natural products.
- The characterization of prealnumycin C-ribosylation offers a new perspective on the biosynthesis of complex glycosylated molecules.
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