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Cover Picture: A Novel Mycolactone from a Clinical Isolate of Mycobacterium ulcerans Provides Evidence for Additional Toxin Heterogeneity as a Result of Specific Changes in the Modular Polyketide Synthase (ChemBioChem 4/2005)
The cover picture shows the structure (in red, right) of the lipophilic polyketide toxin mycolactone obtained from the reference Ghana strain of Mycobacterium ulcerans, the causative agent of the emerging disease Buruli ulcer, and that (in red, left) of a molecular variant of mycolactone newly identified from a clinical isolate of M. ulcerans from China. The new variant bears a single additional methyl group in the sidechain, as shown by mass spectrometry. Also shown at the top is the difference detected between the structural genes; this difference is dictated by a precise acyltransferase (AT) domain swap in the chain-building polyketide synthase, so that a propionate (Pr) unit is recruited rather than an acetate (Ac) unit. Detailed information about this apparent natural example of polyketide biosynthetic engineering is reported by P. Leadley et al. on p. 643 ff.