mycolic

Mycolic refers to a class of extremely long-chain fatty acids known as mycolic acids, which are a defining component of the cell walls of certain bacteria, most notably the genus Mycobacterium. These acids are β-hydroxy fatty acids with very long carbon chains, typically ranging from about 60 to 90 carbon atoms, and they are covalently linked to the arabinogalactan–peptidoglycan matrix to form a dense, waxy outer layer. This mycolyl-arabinogalactan-peptidoglycan complex contributes to the characteristic acid-fast staining properties of mycobacteria and to the markedly low permeability of the cell envelope.

Biosynthesis and structural diversity are distinctive features of mycolates. They are produced by specialized fatty acid synthesis pathways, mainly FAS-I and FAS-II, with additional tailoring steps that yield substituted forms such as methoxymycolates, ketomycolates, and hydroxymycolates. The meromycolate chain length and the presence of cyclopropane rings or other functional groups add to structural diversity and influence cell wall properties. The final formation of mycolic acids involves coordinated enzymatic steps, including polyketide synthases such as Pks13.

Biological and medical significance is considerable. The waxy, lipid-rich cell envelope impedes chemical and immune system access, contributing to virulence and persistence in hosts, as well as intrinsic resistance to many antibiotics. Clinically, mycolic acids underpin acid-fast staining techniques used in diagnostics, and they are targets of antitubercular drugs that interrupt mycolic acid synthesis. Mycolates are most associated with pathogenic mycobacteria but can also be found in related Actinobacteria such as Nocardia.