Geometric isomerization of dietary monounsaturated fatty acids by a cis/trans fatty acid isomerase from Pseudomonas putida KT2440

Pseudomonas putida KT2440 encodes a defense system that rigidifies membranes by a cytochrome c-type cis/trans fatty acid isomerase (CTI). Despite its potential as an industrial biocatalyst for directly regulating the geometric isomerism of monounsaturated fatty acids, its original catalytic and structural properties have remained elusive. In this study, the catalytic nature of wild-type CTI purified P. putida KT2440 against dietary monounsaturated fatty acids was investigated. It showed substrate preference for palmitoleic acid (C_16:1, cis-Δ⁹), along with substrate promiscuity with chain length and double bond position (palmitoleic acid>cis-vaccenic acid>oleic acid). Under determined optimum reaction conditions, its catalytic efficiency (k_cat/K_m) was evaluated as 5.13 × 10² M^-1·sec^-1 against palmitoleic acid. Furthermore, computational predictions of the protein structure revealed its monoheme cytochrome c-type domain and a parasol-like transmembrane domain, suggesting its catalytic mode of action. For effective cis/trans isomerization, the ethylene double bond of monounsaturated fatty acids should be precisely positioned at the heme center of CTI, indicating that its substrate specificity can be determined by the alkyl chain length and the double bond position of the fatty acid substrates. These findings shed light on the potential of CTI as a promising biocatalyst for the food and lipid industry.