4h2h
Crystal structure of an enolase (mandalate racemase subgroup, target EFI-502101) from Pelagibaca bermudensis htcc2601, with bound mg and l-4-hydroxyproline betaine (betonicine)
Structural highlights
FunctionHPBD_SALBH Catalyzes the 2-epimerization of trans-4-hydroxy-L-proline betaine (tHyp-B) to cis-4-hydroxy-D-proline betaine (cHyp-B). Is involved in a catabolic pathway that degrades tHyp-B to alpha-ketoglutarate. This pathway would permit the utilization of tHyp-B as a carbon and nitrogen source in the absence of osmotic stress, since tHyp-B functions as an osmolyte and is not catabolized when it is needed as osmoprotectant. To a lesser extent, can also catalyze the racemization of L-proline betaine.[1] Publication Abstract from PubMedAssigning valid functions to proteins identified in genome projects is challenging: overprediction and database annotation errors are the principal concerns. We and others are developing computation-guided strategies for functional discovery with 'metabolite docking' to experimentally derived or homology-based three-dimensional structures. Bacterial metabolic pathways often are encoded by 'genome neighbourhoods' (gene clusters and/or operons), which can provide important clues for functional assignment. We recently demonstrated the synergy of docking and pathway context by 'predicting' the intermediates in the glycolytic pathway in Escherichia coli. Metabolite docking to multiple binding proteins and enzymes in the same pathway increases the reliability of in silico predictions of substrate specificities because the pathway intermediates are structurally similar. Here we report that structure-guided approaches for predicting the substrate specificities of several enzymes encoded by a bacterial gene cluster allowed the correct prediction of the in vitro activity of a structurally characterized enzyme of unknown function (PDB 2PMQ), 2-epimerization of trans-4-hydroxy-l-proline betaine (tHyp-B) and cis-4-hydroxy-d-proline betaine (cHyp-B), and also the correct identification of the catabolic pathway in which Hyp-B 2-epimerase participates. The substrate-liganded pose predicted by virtual library screening (docking) was confirmed experimentally. The enzymatic activities in the predicted pathway were confirmed by in vitro assays and genetic analyses; the intermediates were identified by metabolomics; and repression of the genes encoding the pathway by high salt concentrations was established by transcriptomics, confirming the osmolyte role of tHyp-B. This study establishes the utility of structure-guided functional predictions to enable the discovery of new metabolic pathways. Discovery of new enzymes and metabolic pathways by using structure and genome context.,Zhao S, Kumar R, Sakai A, Vetting MW, Wood BM, Brown S, Bonanno JB, Hillerich BS, Seidel RD, Babbitt PC, Almo SC, Sweedler JV, Gerlt JA, Cronan JE, Jacobson MP Nature. 2013 Sep 22. doi: 10.1038/nature12576. PMID:24056934[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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