2f98
Crystal structure of the polyketide cyclase AknH with bound substrate and product analogue: implications for catalytic mechanism and product stereoselectivity.
Structural highlights
FunctionDNRD_STRGJ Involved in the biosynthesis of aklavinone which is an important precursor common to the formation of the clinically significant anthracyclines such as carminomycin, daunorubicin (daunomycin), rhodomycin, aclacinomycin T (aklavin) and aclacinomycin A (aclarubicin). These compounds are aromatic polyketide antibiotics that exhibit high cytotoxicity and are widely applied in the chemotherapy of a variety of cancers. Catalyzes the cyclization of aklanonic acid methyl ester to yield aklaviketone. It is also able to use nogalonic acid methyl ester as substrate, but produces exclusively auraviketone with C9-R stereochemistry.[1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAknH is a small polyketide cyclase that catalyses the closure of the fourth carbon ring in aclacinomycin biosynthesis in Streptomyces galilaeus, converting aklanonic acid methyl ester to aklaviketone. The crystal structure analysis of this enzyme, in complex with substrate and product analogue, showed that it is closely related in fold and mechanism to the polyketide cyclase SnoaL that catalyses the corresponding reaction in the biosynthesis of nogalamycin. Similarity is also apparent at a functional level as AknH can convert nogalonic acid methyl ester, the natural substrate of SnoaL, to auraviketone in vitro and in constructs in vivo. Despite the conserved structural and mechanistic features between these enzymes, the reaction products of AknH and SnoaL are stereochemically distinct. Supplied with the same substrate, AknH yields a C9-R product, like most members of this family of polyketide cyclases, whereas the product of SnoaL has the opposite C9-S stereochemistry. A comparison of high-resolution crystal structures of the two enzymes combined with in vitro mutagenesis studies revealed two critical amino acid substitutions in the active sites, which contribute to product stereoselectivity in AknH. Replacement of residues Tyr15 and Asn51 of AknH, located in the vicinity of the main catalytic residue Asp121, by their SnoaL counter-parts phenylalanine and leucine, respectively, results in a complete loss of product stereoselectivity. Crystal structure of the polyketide cyclase AknH with bound substrate and product analogue: implications for catalytic mechanism and product stereoselectivity.,Kallio P, Sultana A, Niemi J, Mantsala P, Schneider G J Mol Biol. 2006 Mar 17;357(1):210-20. Epub 2006 Jan 6. PMID:16414075[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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