Identification and characterization of 4-hexylbenzoic acid and 4-nonyloxybenzoic acid as substrates of CYP102A1.

CYP102A1 is an efficient medium- to long-chain fatty acid hydroxylase that is able to accept a wide range of non-natural substrates which bear no resemblance to the natural ones. 4-Hexylbenzoic acid (HBA) and 4-nonyloxybenzoic acid (NOBA) were identified as CYP102A1 substrates via screening studies using the BD Oxygen Biosensor System. Spectroscopic binding studies showed that these two substrates bind in the active site of CYP102A1 with K(d) values of 2.6 ± 0.1 µM for HBA and 1.9 ± 0.2 µM for NOBA. NADPH consumption rates in the presence of HBA and NOBA were 45 ± 1 min(-1) and 61 ± 1 min(-1), respectively. The coupling efficiency for NADPH was 57% for NOBA, while it was 77% for HBA. During whole-cell biotransformations, HBA was converted into ω-1- and ω-2-hydroxyhexylbenzoic acid, whereas NOBA was oxidized to ω-2-hydroxynonyloxybenzoic acid and ω-2,ω-4-dihydroxynonyloxybenzoic acid. HBA was used as a fatty acid mimic to compare whole-cell biotransformations with cell-free extracts. Whole-cell biotransformations carried out in a biphasic system resulted in 86% conversion of 5 mM HBA, producing 3.8 mM ω-2- and 0.5 mM ω-1-hydroxyhexylbenzoic acid in 4 h with a turnover number of 4.1 min(-1), whereas 100% conversion of 5 mM HBA was obtained in 1 h with crude cell extracts and a cofactor regeneration system, giving a turnover number of 10.5 min(-1).