A comparative analysis of the sugar phosphate cyclase superfamily involved in primary and secondary metabolism.

Sugar phosphate cyclases (SPCs) catalyze the cyclization of sugar phosphates to produce a variety of cyclitol intermediates that serve as the building blocks of many primary metabolites, for example, aromatic amino acids, and clinically relevant secondary metabolites, for example, aminocyclitol/aminoglycoside and ansamycin antibiotics. Feeding experiments with isotopically labeled cyclitols revealed that cetoniacytone A, a unique C(7)N-aminocyclitol antibiotic isolated from an insect endophytic Actinomyces sp., is derived from 2-epi-5-epi-valiolone, a product of SPC. By using heterologous probes from the 2-epi-5-epi-valiolone synthase class of SPCs, an SPC homologue gene, cetA, was isolated from the cetoniacytone producer. cetA is closely related to BE-orf9 found in the BE-40644 biosynthetic gene cluster from Actinoplanes sp. strain A40644. Recombinant expression of cetA and BE-orf9 and biochemical characterization of the gene products confirmed their function as 2-epi-5-epi-valiolone synthases. Further phylogenetic analysis of SPC sequences revealed a new clade of SPCs that might regulate the biosynthesis of a novel set of secondary metabolites.

Structure and biosynthesis of cetoniacytone A, a cytotoxic aminocarba sugar produced by an endosymbiontic Actinomyces.

Cetoniacytone A (1) and some related minor components (2, 6, 7) were produced by Actinomyces sp. (strain Lu 9419), which was isolated from the intestines of a rose chafer (Cetonia aureata). The structures of the novel metabolites were established by detailed spectroscopic analysis. The absolute configuration of 1 was determined by X-ray analysis and derivatisation with chiral acids. 1 exhibits a significant cytotoxicity against selected tumor cell lines. The biosynthesis of 1 was studied by feeding 13C labelled precursors. The results suggest that the characteristic p-C7N skeleton of the aminocarba sugar is formed via the pentose phosphate pathway by cyclisation of a heptulose phosphate intermediate.