Hexaacylillerad

Hexaacylillerad (six-acylated) is a term used in biochemistry to describe a molecule that bears six fatty acyl groups. In many contexts the phrase refers to the lipid A portion of the lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria, where the canonical lipid A is typically hexaacylated.

Structurally, lipid A consists of a disaccharide backbone of glucosamine units, often with phosphate groups and attached fatty acid chains. A hexaacylated lipid A contains six fatty acyl chains, usually arranged as four primary acyl chains derived from 3-hydroxy fatty acids and two additional secondary chains. The exact pattern and length of the chains can vary among species, but six acyl chains is the common form associated with strong immunostimulatory activity.

Biologically, the degree of acylation affects how the molecule is recognized by the host immune system. Hexaacylated lipid A is a potent endotoxin that strongly activates Toll-like receptor 4 (TLR4) in complex with MD-2, triggering inflammatory responses. By contrast, underacylated forms (such as penta- or tetraacylated lipid A) tend to be less endotoxic. This variation has practical implications for vaccine design and adjuvant development; modified lipid A structures with fewer acyl chains often retain immunogenicity while reducing reactogenicity.

Biosynthesis of hexaacylated lipid A involves specific acyltransferases that add the fatty acids to the lipid A backbone. Changes in these enzymatic steps can shift the molecule toward fewer acyl chains, influencing bacterial virulence and host interactions.

See also: lipopolysaccharide, lipid A, acylation, endotoxin.