ADAMTS13 is a plasma metalloproteinase that cleaves von Willebrand factor to smaller, less thrombogenic forms. Deficiency of ADAMTS13 activity in plasma leads to thrombotic thrombocytopenic purpura. ADAMTS13 contains eight thrombospondin type 1 repeats (TSR), seven of which contain a consensus sequence for the direct addition of fucose to the hydroxyl group of serine or threonine. Mass spectral analysis of tryptic peptides derived from human ADAMTS13 indicate that at least six of the TSRs are modified with an O-fucose disaccharide. Analysis of [3 H]fucose metabolically incorporated into ADAMTS13 demonstrated that the disaccharide has the structure glucose-␤1,3-fucose. Mutation of the modified serine to alanine in TSR2, TSR5, TSR7, and TSR8 reduced the secretion of ADAMTS13. Mutation of more than one site dramatically reduced secretion regardless of the sites mutated. When the expression of protein O-fucosyltransferase 2 (POFUT2), the enzyme that transfers fucose to serines in TSRs, was reduced using siRNA, the secretion of ADAMTS13 decreased. A similar outcome was observed when ADAMTS13 was expressed in a cell line unable to synthesize the donor for fucose addition, GDPfucose. Although overexpression of POFUT2 did not affect the secretion of wild-type ADAMTS13, it did increase the secretion of the ADAMTS13 TSR1,2 double mutant but not that of ADAMTS13 TSR1-8 mutant. Together these findings indicate that O-fucosylation is functionally significant for secretion of ADAMTS13.ADAMTS13 is a plasma metalloprotease that cleaves von Willebrand factor to smaller, less thrombogenic fragments. ADAMTS13 is a member of the ADAMTS family of metalloproteases that are characterized by a conserved domain structure. These include a metalloprotease domain, a disintegrin domain, a thrombospondin type 1 repeat (TSR), 2 a cysteinerich domain, and a spacer domain and conclude with a variable number of additional TSRs (1). ADAMTS13 uniquely contains seven additional TSRs and two CUB1 domains at its carboxyl end (2-4) (Fig. 1A). TSRs contain ϳ60 amino acids with conserved tryptophans and cysteines. They were first described in thrombospondin type 1 and are homologous to the properdin repeat found in many components of the complement system. Thrombospondin type 1 is a protein that is thought to play a role in angiogenesis, cell adhesion, and motility (5, 6). Many interactions of thrombospondin-1 are thought to be mediated through amino acids within the TSRs (7). For example, binding of thrombospondin-1 to the endothelial cell protein, CD36, can be inhibited by the peptide CSVTCG, which is found in the TSRs of thrombospondin-1 (8). The three TSRs of thrombospondin-1 have been shown to contain a fucose directly linked to a serine or threonine within a putative consensus sequence of C 1 XX(S/T)C 2 G (where C 1 and C 2 are the 1st and 2nd conserved cysteines in the TSR (9)), which is the putative CD36 binding region. The fucose on the TSRs was further modified with a glucose in ␤1-3 linkage to form a disaccharide (9, 10). Subsequent analysis ...

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The ADAMTS superfamily contains several metalloproteases (ADAMTS proteases) as well as ADAMTS-like molecules that lack proteolytic activity. Their common feature is the presence of one or more thrombospondin type-1 repeats (TSRs) within a characteristic modular organization. ADAMTS like-1/punctin-1 has four TSRs. Previously, O-fucosylation on Ser or Thr mediated by the endoplasmic reticulum-localized enzyme protein-O-fucosyltransferase 2 (POFUT2) was described for TSRs of thrombospondin-1, properdin, and F-spondin within the sequence Cys-Xaa 1 -Xaa 2 -(Ser/Thr)-Cys-Xaa-Xaa-Gly (where the fucosylated residue is underlined). On mass spectrometric analysis of tryptic peptides from recombinant secreted human punctin-1, the appropriate peptides from TSR2, TSR3, and TSR4 were found to bear either a fucose monosaccharide (TSR3, TSR4) or a fucose-glucose disaccharide (TSR2, TSR3, TSR4). Although mass spectral analysis did not unambiguously identify the relevant peptide from TSR1, metabolic labeling of cells expressing TSR1 and the cysteine-rich module led to incorporation of [ 3 H]fucose into this construct. Mutation of the putative modified Ser/Thr residues in TSR2, TSR3, and TSR4 led to significantly decreased levels of secreted punctin-1. Similarly, expression of punctin-1 in Lec-13 cells that are deficient in conversion of GDP-mannose to GDP-fucose substantially decreased the levels of secreted protein, which were restored upon culture in the presence of exogenous L-fucose. In addition, mutation of the single N-linked oligosaccharide in punctin-1 led to decreased levels of secreted punctin-1. Taken together, the data define a critical role for N-glycosylation and O-fucosylation in the biosynthesis of punctin-1. From a broad perspective, these data suggest that O-fucosylation may be a widespread post-translational modification in members of the ADAMTS superfamily with possible regulatory consequences.In humans, the ADAMTS superfamily contains 19 ADAMTS proteases and at least five ADAMTS-like proteins. ADAMTS proteases consist of a metalloprotease zymogen domain attached to a C-terminal ancillary domain. The modular construction of the ancillary domain, which includes one or more thrombospondin-type 1 repeats (TSRs), 2 is a hallmark of the ADAMTS superfamily (1, 2). TSRs were initially discovered in the matricellular protein thrombospondin-1 (3) and were subsequently identified in several other molecules. ADAMTS-like proteins closely resemble the ancillary domains of ADAMTS proteases in their modular content (including the presence of TSRs) and primary sequence but lack the metalloprotease domain, and thus, do not have protease activity (4, 5). ADAMTS-like proteins are not alternatively spliced variants arising from ADAMTS genes, but they are the products of distinct genes. They are present in chordates as well as non-chordates (6), implying conserved functions, although these are presently unknown. Currently, it is considered that some ADAMTS-like proteins may be extracellular matrix components, although a potential ...

Thrombospondin type 1 repeat (TSR) superfamily members regulate diverse biological activities ranging from cell motility to inhibition of angiogenesis. In this study, we verified that mouse protein O-fucosyltransferase-2 (POFUT2) specifically adds O-fucose to TSRs. Using two Pofut2 gene trap lines, we demonstrated that O-fucosylation of TSRs was essential for restricting epithelial to mesenchymal transition in the primitive streak, correct patterning of mesoderm, and localization of the definitive endoderm. Although Pofut2 mutant embryos established anterior/posterior polarity, they underwent extensive mesoderm differentiation at the expense of maintaining epiblast pluripotency. Moreover, mesoderm differentiation was biased towards the vascular endothelial cell lineage. Localization of Foxa2 and Cer1 expressing cells within the interior of Pofut2 mutant embryos suggested that POFUT2 activity was also required for the displacement of the primitive endoderm by definitive endoderm. Notably, Nodal, BMP4, Fgf8, and Wnt3 expression were markedly elevated and expanded in Pofut2 mutants, providing evidence that O-fucose modification of TSRs was essential for modulation of growth factor signaling during gastrulation. The ability of Pofut2 mutant embryos to form teratomas comprised of tissues from all three germ layer origins suggested that defects in Pofut2 mutant embryos resulted from abnormalities in the extracellular environment. This prediction is consistent with the observation that POFUT2 targets are constitutive components of the extracellular matrix (ECM) or associate with the ECM. For this reason, the Pofut2 mutants represent a valuable tool for studying the role of O-fucosylation in ECM synthesis and remodeling, and will be a valuable model to study how post-translational modification of ECM components regulates the formation of tissue boundaries, cell movements, and signaling.

O-Fucose has been described on both epidermal growth factor-like (EGF-like) repeats and Thrombospondin type 1 repeats (TSRs). The enzyme adding fucose to EGF-like repeats, protein O-fucosyltransferase 1 (Pofut1), is a soluble protein located in the lumen of endoplasmic reticulum (ER). A second protein O-fucosyltransferase, Pofut2, quite divergent from its homolog Pofut1, has recently been shown to O-fucosylate TSRs but not EGF-like repeats. To date, Pofut1 genes have only been characterized in human, mouse, and fly, and Pofut2 in mouse, fly, and partially in the nematode Caenorhabditis elegans. Here, we report cDNA sequences and genomic structures of bovine Pofut1 and Pofut2 genes and describe for the first time five alternative spliced transcripts for each gene. Only one transcript for both Pofut1 and Pofut2 encodes an active bovine O-fucosyltransferase. Variant transcript distribution was examined in 13 bovine tissues. Transcripts encoding active forms are ubiquitous, whereas other forms possess a more restricted tissue-expression profile. Sequence comparison and phylogenetic analyses revealed that both Pofut genes are present as a single copy in animal genomes, and their exon-intron organizations are conserved among vertebrates. The last common ancestor of all analyzed bilaterian species would be predicted to possess polyexonic Pofut genes in their genome.