TypIIFAS

TypIIFAS is a term used in biochemistry to denote a proposed subclass of type II fatty acid synthase (FAS) systems. It is distinguished from both the canonical Type II fatty acid synthase arrangements and the Type I multifunctional megasynthases by its modular, ACP-dependent organization. In TypIIFAS, fatty acid elongation relies on separate, typically soluble enzymes that act on an acyl carrier protein (ACP) carrying the growing chain. Condensation is performed by ketoacyl-ACP synthases (KAS) of the II-type (such as FabB/FabF homologs), with individual enzymes providing distinct steps: malonyl transfer (FabD-like), reduction (FabG), dehydration (FabZ/FabA), and enoyl reduction (FabI). The pathway proceeds through sequential cycles with the growing acyl-ACP tethered to ACP rather than existing as a single polypeptide.

Occurrence and genetic organization: TypIIFAS components have been identified in several bacterial genera and, in some cases, in archaea, often in operon-like clusters that include acp, fabD, fabH or fabB/fabF, fabG, fabZ/fabA, and fabI or related reductases. The exact complement of enzymes and their substrate specificities can vary, contributing to differences in chain length, saturation, and branching.

Function and importance: TypIIFAS contributes to membrane lipid biosynthesis and can be adapted for the production of unusual fatty acids. Because the components are discrete enzymes, TypIIFAS offers potential targets for antibiotics and for metabolic engineering aimed at customized lipid products.