Fatty Acid Biosynthesis: Chain‐Length Regulation and Control

Abstract

De novo biosynthesis of fatty acids is an iterative process requiring strict regulation of the lengths of the produced fatty acids. In this review, we focus on the factors determining chain lengths in fatty acid biosynthesis. In a nutshell, the process of chain‐length regulation can be understood as the output of a chain‐elongating C−C bond forming reaction competing with a terminating fatty acid release function. At the end of each cycle in the iterative process, the synthesizing enzymes need to “decide” whether the growing chain is to be elongated through another cycle or released as the “mature” fatty acid. Recent research has shed light on the factors determining fatty acid chain length and has also achieved control over chain length for the production of the technologically interesting short‐chain (C4–C8) and medium‐chain (C10–C14) fatty acids.

A mass spectrometry‐based high‐throughput screening method for engineering fatty acid synthases with improved production of medium‐chain fatty acids

“…The physiochemical properties of these molecules depend on the chemical structures of fatty acyl chains, such as chain length, branching pattern, and degree of unsaturation. For microbially produced MCFAs, however, it remains a major challenge to control acyl chain compositions via enzymatic and metabolic engineering (Heil, Wehrheim, Paithankar, & Grininger, 2019; Hu, Zhu, Nielsen, & Siewers, 2019). Directed evolution has demonstrated wide successes in engineering biosynthetic selectivity via iterative rounds of large‐scale genetic mutagenesis and phenotypic screening, but no general platform is currently available to analyze FFA‐producing strain libraries in a high‐throughput manner (Cobb, Sun, & Zhao, 2013).…”

“…For long‐chain fatty acids (C14, C16, and C18), WT had more production than any of the tested mutants (Figure 4b), which correlated well with the relative ratios of FFA molecules quantified using MALDI‐ToF MS. We then speculated the molecular mechanisms behind these candidates. Mutagenesis at M1251 site can potentially increase the steric hindrance between the inner and outer KS domains, thus preventing short acyl chains from elongation (Christensen, Kragelund, von Wettstein‐Knowles, & Henriksen, 2007; Gajewski, Buelens, et al, 2017; Heil et al, 2019; Johansson et al, 2008). Mutagenesis at the neighboring G1250 site can presumably interfere with the conformational flexibility or lower the dynamic coverage of M1251 site, consequently reducing the available inner volume (Aritomi et al, 2004; Gajewski, Buelens, et al, 2017; Heil et al, 2019).…”

“…Mutagenesis at M1251 site can potentially increase the steric hindrance between the inner and outer KS domains, thus preventing short acyl chains from elongation (Christensen, Kragelund, von Wettstein‐Knowles, & Henriksen, 2007; Gajewski, Buelens, et al, 2017; Heil et al, 2019; Johansson et al, 2008). Mutagenesis at the neighboring G1250 site can presumably interfere with the conformational flexibility or lower the dynamic coverage of M1251 site, consequently reducing the available inner volume (Aritomi et al, 2004; Gajewski, Buelens, et al, 2017; Heil et al, 2019). Mutagenesis at V1254 site was found to interact frequently with the C16‐FA substrate acyl chain after docking (Heil et al, 2019; Rigouin et al, 2017).…”

“…Mutagenesis at the neighboring G1250 site can presumably interfere with the conformational flexibility or lower the dynamic coverage of M1251 site, consequently reducing the available inner volume (Aritomi et al, 2004; Gajewski, Buelens, et al, 2017; Heil et al, 2019). Mutagenesis at V1254 site was found to interact frequently with the C16‐FA substrate acyl chain after docking (Heil et al, 2019; Rigouin et al, 2017). Mutagenesis at F1279 site would disrupt the KS binding channel from the opposite side of M1251, hence limiting the space for fatty acid acyl chain elongation (Gajewski, Pavlovic, et al, 2017; Heil et al, 2019).…”

“…Mutagenesis at V1254 site was found to interact frequently with the C16‐FA substrate acyl chain after docking (Heil et al, 2019; Rigouin et al, 2017). Mutagenesis at F1279 site would disrupt the KS binding channel from the opposite side of M1251, hence limiting the space for fatty acid acyl chain elongation (Gajewski, Pavlovic, et al, 2017; Heil et al, 2019).…”