Identification of the herboxidiene biosynthetic gene cluster in Streptomyces chromofuscus ATCC 49982

Abstract

The 53-kb biosynthetic gene cluster for the novel anticholesterol natural product herboxidiene was identified in Streptomyces chromofuscus ATCC 49982 by genome sequencing and gene inactivation. In addition to herboxidiene, a biosynthetic intermediate, 18-deoxy-herboxidiene, was also isolated from the fermentation broth of S. chromofuscus ATCC 49982 as a minor metabolite.

Fig 1

The proposed herboxidiene biosynthetic pathway and the sequenced biosynthetic gene cluster. (A) Proposed biosynthetic pathway of compound 1. (B) Organization of the herboxidiene biosynthetic gene cluster. ORFs involved in herboxidiene biosynthesis are shown as gray (regulatory and tailoring enzymes) and black (PKS) arrows.

Fig 2

Alignment of divergent motifs in the AT and KR domains of the herboxidiene PKS. (A) Methylmalonyl-CoA-specific and malonyl-CoA-specific ATs. The underlined residues are associated with malonyl-CoA and methylmalonyl-CoA specificity. (B) Alignment of the conserved motifs in KRs. KR1 belongs to A1-type KRs (1, no LDD; 2, W; 3, no H). KR3, -4, -5, -6, -7, and -8 fall into the B1 type (1, LDD; 4, no P). The conserved motifs of KR2 are obscure, and the type of this domain remains unclear.

Fig 3

HPLC analysis of herboxidiene biosynthesis in S. chromofuscus ATCC 49982 and mHER1001 at 238 nm. Traces: i, products of S. chromofuscus ATCC 49982; ii, products of S. chromofuscus mHER1001; iii, purified standard of compound 1; iv, purified standard of compound 2.