Structural enzymology of the biosynthesis of polyketide antibiotics

Anthracyclines are an important group of aromatic antibiotics that exhibit antitumour activity, which makes them useful in treatment of various cancers. They are synthesised in the polyketide biosynthetic pathway as secondary metabolites by different Streptomyces species. An increasing number of anthracyclines have however been shown to exhibit cardiotoxic side-effects. The genetics and enzymology of this pathway has recently attracted considerable interest, not at least with the possible prospect for the production of novel antibiotics.

In this thesis some of the enzymes involved in biosynthesis of anthracyclines have been studied by protein crystallography and biochemical methods. The structure of SnoaL, a stereospecific cyclase was determined to a resolution of 1.35 A as a complex with a product analogue. SnoaL belongs to a hitherto uncharacterised family of enzymes with alpha+beta barrel like fold and catalyses a novel form of intramolecular aldolcondensation. The structure of the methylesterase RdmC in complex with product analogue shows the common alpha/beta hydrolase fold and contains a catalytic SerHis-Asp triad. RdmB is a hydroxylase built up by a Rossman-like fold common to methyltransferases. The enzyme utilizes the SAM moiety in a novel way as a cofactor in the hydroxylation reaction. DnrK is a methyltransferase with a structure very similar to that of RdmB.

RdmB and DnrK are thus two enzymes sharing the same fold but catalysing different reactions. They are illustrative examples of two enzymes evolved through divergent evolution. A common feature to all the enzymes studied in the thesis is that they bind their anthracycline substrates mainly through hydrophobic interactions with the involvement of only a few hydrogen bonds. Many of the enzymes have a very broad substrate specificity which might be due to these features.

List of scientific papers

I. Jansson A, Niemi J, Mantsala P, Schneider G (2003). Crystal structure of aclacinomycin methylesterase with bound product analogues: implications for anthracycline recognition and mechanism. J Biol Chem. 278(40): 39006-13. Epub 2003 Jul 23
https://pubmed.ncbi.nlm.nih.gov/12878604

II. Jansson A, Niemi J, Mantsala P, Schneider G (2003). Crystallization and preliminary X-ray diffraction studies of aclacinomycin-10-methyl esterase and aclacinomycin-10-hydroxylase from Streptomyces purpurascens. Acta Crystallogr D Biol Crystallogr. 59(Pt 9): 1637-9.
https://pubmed.ncbi.nlm.nih.gov/12925797

III. Jansson A, Niemi J, Lindqvist Y, Mantsala P, Schneider G (2003). Crystal structure of aclacinomycin-10-hydroxylase, a S-adenosyl-L-methionine-dependent methyltransferase homolog involved in anthracycline biosynthesis in Streptomyces purpurascens. J Mol Biol. 334(2): 269-80.
https://pubmed.ncbi.nlm.nih.gov/14607118

IV. Sutana A, Kallio P, Jansson A, Niemi J, Mantsala P, Schneider G (2004). Crystallisation and preliminary crystallographic data of SnoaL, a polyketide cyclase in nogalamycin biosynthesis. Acta Crystallogr D Biol Crystallogr. [Accepted]

V. Sultana A, Kallio P, Jansson A, Wang JS, Niemi J, Mantsala P, Schneider G (2004). Structure of the polyketide cyclase SnoaL reveals a novel mechanism for enzymatic aldol condensation. EMBO J. 23(9): 1911-21. Epub 2004 Apr 08
https://pubmed.ncbi.nlm.nih.gov/15071504

VI. Jansson A, Koskiniemi H, Mantsala P, Niemi J, Schneider G (2004). Crystal structure of a ternary complex of DnrK, a methyltransferase in daunorubicin biosynthesis with bound products. [Manuscript]