Carboxyl Formation from Methyl via Triple Hydroxylations by XiaM in Xiamycin A Biosynthesis.

The P450 enzyme XiaM was identified as a candidate to form the C-24 carboxyl group in xiamycin A (1). Alteration of medium composition led to the discovery of four new compounds from the ΔxiaMand the ΔxiaK(encoding an aromatic ring hydroxylase) mutants. Biotransformation experiments revealed that XiaM was capable of converting a methyl group to a carboxyl group through diol and aldehyde intermediates. [ABSTRACT FROM AUTHOR]