Identification of Alp1U and Lom6 as epoxy hydrolases and implications for kinamycin and lomaiviticin biosynthesis

Abstract

The naturally occurring diazobenzofluorenes, kinamycins, fluostatins and lomaiviticins, possess highly oxygenated A-rings, via which the last forms a dimeric pharmacophore. However, neither the A-ring transformation nor the dimerization mechanisms have been explored thus far. Here we propose a unified biosynthetic logic for the three types of antibiotics and verify one key reaction via detailed genetic and enzymatic experiments. Alp1U and Lom6 from the kinamycin and lomaiviticin biosynthesis, respectively, are shown to catalyse epoxy hydrolysis on a substrate that is obtained by chemical deacetylation of a kinamycin-pathway-derived intermediate. Thus, our study provides the first evidence for the existence of an epoxy intermediate in lomaiviticin biosynthesis. Furthermore, our results suggest that the dimerization in the lomaiviticin biosynthesis proceeds after dehydration of a product generated by Lom6.

Figure 1. The proposed biosynthetic pathway for kinamycin class antibiotics.

Figure 2. HPLC profiles of crude extracts from mutants studied in this work.

Trace A, the starting strain producing kinamycin D (3); trace B, ΔΔalp1U producing epoxykinamycin FL-120B′ (4); trace C, ΔΔalp1U::alp1U restoring the production of 3.

Figure 3. HPLC analysis of enzymatic reactions.

Trace A, standard epoxykinamycin FL-120B′ (4); trace B, 4 with Alp1U, producing kinamycin E (5); trace C, 4 with Lom6.

Figure 4. HPLC traces of enzymatic reactions.

Trace A, epoxykinamycin FL-120B′ (4) treated with 0.1 N LiOH, forming epoxykinamycin (1); trace B, kinamycin E (5) treated with 0.1 N LiOH forming kinamycin F (2); trace C, standard 1; trace D, 1 with Lom6 in 50 min producing 2; trace E, 1 with Alp1U in 10 min producing 2.