Conserved residues Arg188 and Asp302 are critical for active site organization and catalysis in human ABO(H) blood group A and B glycosyltransferases.

Homologous glycosyltransferases GTA and GTB perform the final step in human ABO(H) blood group A and B antigen synthesis by transferring the sugar moiety from donor UDP-GalNAc/UDP-Gal to the terminal H antigen disaccharide acceptor. Like other GT-A fold family 6 glycosyltransferases, GTA and GTB undergo major conformational changes in two mobile regions, the C-terminal tail and internal loop, to achieve the closed, catalytic state. These changes are known to establish a salt bridge network among conserved active site residues Arg188, Asp211 and Asp302, which move to accommodate a series of discrete donor conformations while promoting loop ordering and formation of the closed enzyme state.

Glycosyltransfer in mutants of putative catalytic residue Glu303 of the human ABO(H) A and B blood group glycosyltransferases GTA and GTB proceeds through a labile active site.

The homologous glycosyltransferases α-1,3-N-acetylgalactosaminyltransferase (GTA) and α-1,3-galactosyltransferase (GTB) carry out the final synthetic step of the closely related human ABO(H) blood group A and B antigens. The catalytic mechanism of these model retaining enzymes remains under debate, where Glu303 has been suggested to act as a putative nucleophile in a double displacement mechanism, a local dipole stabilizing the intermediate in an orthogonal associative mechanism or a general base to stabilize the reactive oxocarbenium ion-like intermediate in an SNi-like mechanism. Kinetic analysis of GTA and GTB point mutants E303C, E303D, E303Q and E303A shows that despite the enzymes having nearly identical sequences, the corresponding mutants of GTA/GTB have up to a 13-fold difference in their residual activities relative to wild type.

A preclinical study of the safety and efficacy of Occlusin™ 500 Artificial Embolization Device in sheep.

Introduction: This study evaluated the safety, effectiveness, and biodegradation of a new embolic agent, Occlusin™ 503 Artificial Embolization Device (OCL 503). The agent consists of biodegradable poly-lactic-co-glycolic acid microspheres (150-212 μm) coated with type I bovine collagen and was compared with Embosphere® Microspheres (300-500 μm) in this controlled study of uterine artery embolization (UAE) in sheep.

Methods: Unilateral UAE was performed in 32 adult ewes randomly assigned.

Cysteine-to-serine mutants dramatically reorder the active site of human ABO(H) blood group B glycosyltransferase without affecting activity: structural insights into cooperative substrate binding.

A common feature in the structures of GT-A-fold-type glycosyltransferases is a mobile polypeptide loop that has been observed to participate in substrate recognition and enclose the active site upon substrate binding. This is the case for the human ABO(H) blood group B glycosyltransferase GTB, where amino acid residues 177-195 display significantly higher levels of disorder in the unliganded state than in the fully liganded state. Structural studies of mutant enzymes GTB/C80S/C196S and GTB/C80S/C196S/C209S at resolutions ranging from 1.

ABO(H) blood group A and B glycosyltransferases recognize substrate via specific conformational changes.

The final step in the enzymatic synthesis of the ABO(H) blood group A and B antigens is catalyzed by two closely related glycosyltransferases, an alpha-(1-->3)-N-acetylgalactosaminyltransferase (GTA) and an alpha-(1-->3)-galactosyltransferase (GTB). Of their 354 amino acid residues, GTA and GTB differ by only four "critical" residues. High resolution structures for GTB and the GTA/GTB chimeric enzymes GTB/G176R and GTB/G176R/G235S bound to a panel of donor and acceptor analog substrates reveal "open," "semi-closed," and "closed" conformations as the enzymes go from the unliganded to the liganded states.

A single point mutation reverses the donor specificity of human blood group B-synthesizing galactosyltransferase.

Blood group A and B antigens are carbohydrate structures that are synthesized by glycosyltransferase enzymes. The final step in B antigen synthesis is carried out by an alpha1-3 galactosyltransferase (GTB) that transfers galactose from UDP-Gal to type 1 or type 2, alphaFuc1-->2betaGal-R (H)-terminating acceptors. Similarly the A antigen is produced by an alpha1-3 N-acetylgalactosaminyltransferase that transfers N-acetylgalactosamine from UDP-GalNAc to H-acceptors.