4V2P

Ketosynthase MxnB

Summary for 4V2P

• Entry DOI: 10.2210/pdb4v2p/pdb
• Descriptor: KETOSYNTHASE, PHOSPHATE ION, (4S)-2-METHYL-2,4-PENTANEDIOL, ... (6 entities in total)
• Functional Keywords: transferase, ketosynthase, myxopyronin
• Biological source: MYXOCOCCUS FULVUS
• Total number of polymer chains: 2
• Total formula weight: 78911.55

Authors

Koehnke, J. (deposition date: 2014-10-13, release date: 2015-08-26, Last modification date: 2024-10-16)

Primary citation

Sucipto, H.,Sahner, J.H.,Prusov, E.,Wenzel, S.C.,Hartmann, R.W.,Koehnke, J.,Muller, R.
In vitro reconstitution of alpha-pyrone ring formation in myxopyronin biosynthesis.
Chem Sci, 6:5076-5085, 2015

PubMed Abstract: Myxopyronins are α-pyrone antibiotics produced by the terrestrial bacterium Mx f50 and possess antibacterial activity against Gram-positive and Gram-negative pathogens. They target the bacterial RNA polymerase (RNAP) "switch region" as non-competitive inhibitors and display no cross-resistance to the established RNAP inhibitor rifampicin. Recent analysis of the myxopyronin biosynthetic pathway led to the hypothesis that this secondary metabolite is produced from two separate polyketide parts, which are condensed by the stand-alone ketosynthase MxnB. Using assays we show that MxnB catalyzes a unique condensation reaction forming the α-pyrone ring of myxopyronins from two activated acyl chains in form of their β-keto intermediates. MxnB is able to accept thioester substrates coupled to either -acetylcysteamine (NAC) or a specific carrier protein (CP). The turnover rate of MxnB for substrates bound to CP was 12-fold higher than for NAC substrates, demonstrating the importance of protein-protein interactions in polyketide synthase (PKS) systems. The crystal structure of MxnB reveals the enzyme to be an unusual member of the ketosynthase group capable of binding and condensing two long alkyl chains bound to carrier proteins. The geometry of the two binding tunnels supports the biochemical data and allows us to propose an order of reaction, which is supported by the identification of novel myxopyronin congeners in the extract of the producer strain. Insights into the mechanism of this unique condensation reaction do not only expand our knowledge regarding the thiolase enzyme family but also opens up opportunities for PKS bioengineering to achieve directed structural modifications.

PubMed: 29308173
DOI: 10.1039/c5sc01013f

Experimental method

X-RAY DIFFRACTION (1.67 Å)