Primary and secondary metabolism, and post-translational protein modifications, as portrayed by proteomic analysis of Streptomyces coelicolor.

The newly sequenced genome of Streptomyces coelicolor is estimated to encode 7825 theoretical proteins. We have mapped approximately 10% of the theoretical proteome experimentally using two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Products from 770 different genes were identified, and the types of proteins represented are discussed in terms of their annotated functional classes. An average of 1.2 proteins per gene was observed, indicating extensive post-translational regulation. Examples of modification by N-acetylation, adenylylation and proteolytic processing were characterized using mass spectrometry. Proteins from both primary and certain secondary metabolic pathways are strongly represented on the map, and a number of these enzymes were identified at more than one two-dimensional gel location. Post-translational modification mechanisms may therefore play a significant role in the regulation of these pathways. Unexpectedly, one of the enzymes for synthesis of the actinorhodin polyketide antibiotic appears to be located outside the cytoplasmic compartment, within the cell wall matrix. Of 20 gene clusters encoding enzymes characteristic of secondary metabolism, eight are represented on the proteome map, including three that specify the production of novel metabolites. This information will be valuable in the characterization of the new metabolites.

Biosynthesis of trichothecene mycotoxins: cell-free epoxidation of a trichodiene derivative.

A cell-free enzyme system from cultures of Fusarium culmorum catalyses the 12,13-epoxidation of semi-synthetic 9 beta,10 beta-epoxytrichodiene to 9 beta,10 beta;12,13-diepoxytrichodiene. This enzyme activity may be involved in the biosynthesis of trichothecene mycotoxins and since the 12,13-epoxide is known to be essential for toxicity, the enzyme activity probably confers the toxic properties associated with this group of mycotoxins. The epoxidase requires NADPH and molecular oxygen, is inhibited by carbon monoxide, and thus appears to be a cytochrome P-450-dependent mono-oxygenase. Whole cell cultures of the fungus carry out the same biotransformation, and in addition hydroxylate the diepoxide product at position 3, yielding 3 alpha-hydroxy-9 beta,10 beta;12,13-diepoxytrichodiene.