Catalyzes the reaction that attaches fucose through an O-glycosidic linkage to a conserved serine or threonine residue in the consensus sequence C1-X-X-S/T-C2 of thrombospondin type I repeats (TSRs) where C1 and C2 are the first and second cysteines of the repeat, respectively (PubMed:22588082). O-fucosylates members of several protein families including the ADAMTS, the thrombospondin (TSP) and spondin families (Probable) (PubMed:17395588). Required for the proper secretion of ADAMTS family members such as ADAMTSL1 and ADAMTS13 (PubMed:17395589, PubMed:17395588). The O-fucosylation of TSRs is also required for restricting epithelial to mesenchymal transition (EMT), maintaining the correct patterning of mesoderm and localization of the definite endoderm (By similarity). GDP-beta-L-fucose + L-seryl-[protein] = 3-O-(alpha-L-fucosyl)-L-seryl-[protein] + GDP + H(+) GDP-beta-L-fucose + L-threonyl-[protein] = 3-O-(alpha-L-fucosyl)-L-threonyl-[protein] + GDP + H(+) Inhibited by EDTA and by Zn(2+). Protein modification; protein glycosylation. Mainly located in the endoplasmic reticulum. Isoform A is expressed in fetal liver and peripheral blood lymphocytes. Isoform B is expressed in spleen, lung, testis, bone marrow, thymus, pancreas, prostate, fetal brain, fetal liver and fetal kidney. Isoform C is expressed in brain, heart, spleen, liver, lung, stomach, testis, placenta, skin, thymus, pancreas, mammary gland, prostate, fetal brain, fetal liver and fetal heart. Belongs to the glycosyltransferase 68 family. Extended N-terminus. Extended N-terminus. Peptide-O-fucosyltransferase 2