2â²-Fucosyllactose (2â²-FL) is a fucosylated neutral trisaccharide composed of <small>L</small>-fucose, <small>D</small>-galactose, and <small>D</small>-glucose units. It is the most prevalent human milk oligosaccharide (HMO) naturally present in human breast milk, making up about 30% of all of HMOs. It was first discovered in the 1950s in human milk. The oligosaccharide's primary isolation technique has been in use since 1972.
2â²-FL consists of an L-fucose monomer in the ñ stereochemical configuration linked at the first carbon to a monomer of D-galactose in the ò stereochemical configuration at the second carbon, which is in turn linked at the first carbon to a monomer of D-glucose (which may be in either the ñ or ò configuration) at the fourth carbon.
The compound may be biosynthesized in quantity using E. coli.
Human systemic metabolism of intact 2'-FL is limited. Like other HMOs, it is resistant to human digestive enzymes in the upper gut, meaning it reaches the colon relatively intact.
The key site of 2'-FL metabolism is the intestinal microbiome. First, fucose is cleaved by ñ-fucosidases produced by gut bacteria such as Bifidobacterium spp. and Akkermansia spp.. The remaining lactose moiety is processed by ò-galactosidases and other glycosidases.
Further microbial fermentation results in short-chain fatty acids, such as acetate, as well as lactate, 1,2-propanediol, and butyrate.
As with many other oligosaccharides, a characteristic of 2â²-FL is its ability to protect against infectious diseases by preventing epithelial-level adhesion of toxins and pathogens. 2â²-FL stimulates the growth of certain bifidobacteria and upregulation of receptors which collectively lend to toxic and pathogenic protection; this is most prevalent in infants. Among the pathogens that 2â²-FL is known to protect against are Campylobacter jejuni, Salmonella enterica (serotype Typhimurium), and Helicobacter pylori.