Involvement of LH3 and GLT25D1 for glucosyl-galactosyl-hydroxylation on non-collagen-like domain of FGL1.

Glucosyl-galactosyl-hydroxylation (GGH) is one type of post-translational modification, which is mainly observed in collagen-like domain-containing proteins. Using LC-MS/MS analysis, we found a GGH-like modification at Lys65 of fibrinogen-like protein 1 (FGL1), although it does not contain a collagen-like domain. To identify the glycosyltransferases responsible for this modification, we established LH3/GLT25D1-knockout FGL1-overexpressing HT1080 cell lines. The result showed that knockout of LH3 or GLT25D1 significantly inhibited the glycosylation. Furthermore, deficiency of GGH by point mutation of the FGL1 protein or knockout of the GGH-related glycosyltransferase reduced FGL1 protein levels. Taken together, these data indicate that Lys65 of FGL1 is glucosyl-galactosyl-hydroxylated by LH3 and GLT25D1. Our results provide novel insights to regulate various FGL1 functions.