FUT10 and FUT11 as Novel <i>O</i>-fucosyltransferases

In humans, there are 13 identified genes for fucosyltransferases, and their activities are as follows: 1-2 linkage to Gal (FUT1, 2) and 1-3/4 linkage to lactosamine GlcNAc (FUT3-7, 9), 1-6 linkage to the reducing end of N-linked glycans (FUT8), and the O-fucosyltransferases (POFUT) POFUT1 and POFUT2 (FUT12 and FUT13), which are responsible for modifying protein Ser/Thr residues, were previously identified.On the other hand, the substrates, and activities of two enzymes, FUT10 and FUT11, which were initially identified as 1,3/4-fucosyltransferases based on sequence information, have remained obscure.This section presents a report demonstrating that FUT10 and FUT11 are, in fact, novel protein O-fucosyltransferases [Hao et al. (2025) Nat.Chem.Biol.21, 598-610].The authors have recently reported that the N-terminal elastin microfibril interface (EMI) domain of Multimerin-1 (MMRN1) released from platelets is a novel O-fucosylation site for platelet proteome analysis.In that report, it was shown that the EMI domain of MMRN1 is critical for protein-protein interactions and MMRN1 secretion.Furthermore, it has been shown that O-fucosylation of the EMI domain occurs independently of the known O-fucosyltransferases POFUT1 and POFUT2, suggesting the presence of an unknown O-fucosyltransferase [Houlahan et al. (2024) Mol.Cell Proteomics 23, 100717].The authors performed additional investigations into the MMRN1 O-fucosylation.They identified a second O-fucosylation site in the N-terminal EMI domain, T265, in addition to T216, which was initially reported, and a C-terminal EGF domain, T1055.Fucosylation of the EMI domain was confirmed to be a POFUT1/2-independently modification.They screened the interaction of all 13 human fucosyltransferases with the N-terminal EMI domain of MMRN1 using the structure prediction software AlphaFold2-multimer and AlphaFold3.The screening results suggest that only FUT10 and FUT11 can form reliable complex structures with the EMI domain and that the GDP-binding site on the enzyme is in close contact with the EMI domain fucosylation site.These interactions were supported by the fact that both FUT10 and FUT11 were successfully enriched by coimmunoprecipitation with the EMI domain of MMRN1.The O-fucosyltransferase activity of FUT10 and FUT11 in the EMI domain was verified using purified recombinant proteins.The results showed that FUT10 and FUT11 function independently as POFUT by adding fucose to both the T216 and T265 fucosylation sites in the EMI domain of MMRN1.In addition, O-fucose in the MMRN1 EMI domain expressed in