The α1→3 fucosylation at the penultimate GlcNAc catalyzed by fucosyltransferase VII is blocked by internally fucosylated residue in sialosyl long-chain poly-LacNAc:: Enzymatic basis for expression of physiological E-selectin epitope

Sialosyl-fucosyl poly-LacNAc without sialosyl-Le(x) epitope in myeloid cell line HL60 was shown to be the ligand for E-selectin-dependent adhesion, particularly under dynamic flow conditions, in our previous study (Handa K, Stroud MR, Hakomori S, Biochemistry 36, 12412-12420, 1997). HL60 cells express only fucosyltransferase (FT) TV and VII. X(3)NeuAcVII(3)FucnLc(10), a representative component showing E-selectin-dependent binding under dynamic flow conditions, is not alpha 1 --> 3 fucosylated at the penultimate GlcNAc catalyzed by FT-VII, but is alpha 1 --> 3 fucosylated at the internal GlcNAc catalyzed by FT-IV. VI(3)NeuAcnLc(6) is converted to VI(3)NeuAcIII(3)FucnLc(6) by FT-IV, but is also converted to VI(3)NeuAcV(3)FucnLc(6) by FT-VII. Thus, penultimate fucosylation catalyzed by FT-VII is not restricted for nLc(6) backbone, but is highly restricted for nLc(10) backbone. The cooperative effect of FT-IV and FT-VII for synthesis of poly-LacNAc having sialosyl-Le(x) with internal fucosylation may be blocked or highly restricted in poly-LacNAc having more than two LacNAc units, because preferential alpha 1 --> 3 fucosylation by FT-IV takes place at internal GlcNAc, inhibiting penultimate fucosylation by FT-VII. (C) 1998 Academic Press.