hydroxymycolates

Hydroxymycolates are a class of mycolic acids characterized by the presence of hydroxyl groups within their exceptionally long hydrocarbon chains. They constitute a subset of mycolates found in the cell envelopes of various actinobacteria, most notably mycobacteria and related genera such as Nocardia and Corynebacterium. Mycolic acids themselves are very long-chain fatty acids, typically around 60 to 90 carbon atoms, that form a major component of the mycobacterial cell wall and contribute to its impermeability and acid-fast staining. Hydroxymycolates add additional polarity to these lipid structures and are incorporated into cell-wall lipids, including trehalose-containing glycolipids, or exist as free or esterified derivatives.

Occurrence and diversity: The presence and specific structure of hydroxy mycolates vary among species and strains. They are used in chemotaxonomy to help distinguish certain mycobacterial species. Analytical identification usually involves extraction of cell-wall lipids followed by conversion to methyl esters and analysis by chromatographic methods such as gas chromatography–mass spectrometry.

Biogenesis and function: Mycolic acids are synthesized by bacterial fatty acid synthase systems (FAS-I and FAS-II) with specialized enzymes that generate the meromycolate chains and attach them to glycerol backbones or trehalose. Hydroxylation introduces hydroxyl groups at defined positions, influencing the physical properties of the cell envelope. These modifications affect cell-wall permeability, interactions with host factors, and may modulate susceptibility to certain antibiotics and immune responses.

Clinical and research relevance: Hydroxymycolates are studied to understand cell-wall architecture, taxonomy, and pathogenesis of mycobacterial infections. Their lipid profiles aid in species identification and in investigations of lipidomics in clinical isolates.