Characterization of the C‐terminal region of molecular forms of human milk bile salt‐stimulated lipase

Abstract

Bile salt‐stimulated lipase (BSSL) in human milk exists in multiple molecular forms and it has been shown that approximately one‐third of lactating mothers secrete two forms. Aim: to determine the structural features of BSSL that may give rise to this heterogeneity. Methods: Oligosaccharides present in the proline‐rich region in the C‐terminus of BSSL were investigated using deglycosylating enzymes and lectin affinity probing to determine the origin of the multiple molecular forms. Results: It was found that the variability in the molecular mass of BSSL is due predominantly to glycosylation. The molecular forms contain similar sugar chains; all forms possess the core disaccharide Galβ1‐3GalNAc and β‐D‐galactose, fucose linked at α1‐6 and sialic acid linkage α2‐3 to galactose. Conclusion: The molecular mass difference in the BSSL molecular forms cannot be attributed to the type of carbohydrate moiety in the sugar chains of the N‐ and O‐linked sites suggesting that the differences arise from the extent or quantity of glycosylation. The oligosaccharides in the C‐terminal region contain Lewis x and b and, less prominently, Lewis a antigenic structures. Owing to the presence of these blood‐group‐related antigenic determinants, the C‐terminal region of BSSL may have an adhesive function in cell‐cell interactions.

Bile Salt-Stimulated Lipase from Human Milk Binds DC-SIGN and Inhibits Human Immunodeficiency Virus Type 1 Transfer to CD4 + T Cells

“…The sequence coverage was 32% and the probability-based molecular weight search score 199 (with protein scores greater than 76 considered significant). The identification of BSSL is in accordance with the observation that the protein expresses Le X (27).…”

“…Exon 11 encodes on average 16 repeat domains of 11 amino acids (amino acids 536 to 711) at the C terminus, which contains a high number of O glycosylation sites, while the N terminus contains only one potential N glycosylation site (Asn 187) (1,37). Variant isoforms of BSSL have been shown to differ in the number of repeats at the C terminus of the molecule (24,41), which has been shown to be the domain with a high expression of Le X (27), likely explaining the observed correlation between Le X expression and BSSL size. In accordance with our observation, it has been shown that the expression of Le X can vary between mothers (20).…”

“…Neonates normally secrete only small amounts of colipase-dependent pancreatic lipase into the duodenum (14), so gastric lipase as well as BSSL in human milk markedly enhances fat digestion in the newborn (3). Pancreatic BSSL and human milk BSSL were shown to be identical at the amino acid level (19,31) while substantially varying in their carbohydrate contents (26,43), with Le X being present at the C terminus of BSSL (20,27). BSSL is also present in testes and adrenals (21) and blood plasma of humans (25).…”

“…Bile salt-stimulated lipase (BSSL) is a Le X -carrying glycoprotein (27) secreted by the pancreas and activated by bile salts in the intestine. BSSL is also expressed by the mammary gland and present in human milk (4) at a concentration of between 100 and 200 g/ml (42).…”

Bile salt dependent lipase promotes intestinal adaptation in rats with massive small bowel resection

“…Bile salt dependent lipase (BSDL) is an LeX-carrying glycoprotein secreted by the pancreas and activated by bile salts in the intestine [9]. BSDL is also expressed by the mammary gland and is present in human milk at a concentration between 100 and 200 μg/ml [10,11].…”