Reactome: A Curated Pathway Database

Galactosylation of collagen propeptide hydroxylysines by procollagen galactosyltransferases 1, 2.

Stable Identifier
Homo sapiens
Locations in the PathwayBrowser

Hydroxylysine glycosides are specific to collagen. Collagen glycosylation takes place in the endoplasmic reticulum before triple-helix formation. Either galactose or glucose-galactose are attached to approximately one third of hydroxylysine residues by specific transferases, beta(1-O)galactosyl- and alpha(1-2)glucosyltransferase, forming galactosyl hydroxylysine (Gal-Hyl) and glucosyl-galactosyl hydroxylysine (Glu-Gal-Hyl) respectively. The genes GLT25D1 and GLT25D2 encode galactosyltransferases that are active with various types of collagen and the serum mannose-binding lectin MBL, which also contains a collagen domain. GLT25D1 gene is constitutively expressed in human tissues, whereas the GLT25D2 gene was found to be expressed only at low levels in the nervous system. These galactosyltransferases convert 5-hydroxylysine to 5-galactosyl hydroxylysine (Gal-Hyl). The extent of hydroxylysine galactosylation is variable between collagen types and locations; it is particularly common in bone type I collagen (Al-Dehaimi et al. 1999). Although the fraction of hydroxylysine residues that are glycosylated does not differ between skin and bone (the major sources of type I collagen) the pattern of hydroxylysine glycosylation is different. Glu-Gal-Hyl predominates in skin, where the Glu-Gal-Hyl/Gal-Hyl ratio is approximately 2 (Pinnell et al. 1971), whereas Gal-Hyl predominates in bone, where the Glu-Gal-Hyl/Gal-Hyl ratio is 0.47 (Krane et al. 1977).

Literature References
Participant Of
This entity is regulated by:
Title Physical Entity Activity
procollagen galactosyltransferase activity of Procollagen galactosyltransferases [endoplasmic reticulum lumen] Procollagen galactosyltransferases [endoplasmic reticulum lumen] procollagen galactosyltransferase activity (0050211)
Orthologous Events