Archer-Hartmann, S. A. | bioRxiv Science

bioRxiv2020

Structure of the Xylan O-Acetyltransferase AtXOAT1 Reveals Molecular Insight into Polysaccharide Acetylation in Plants

Acetylation of biomolecules is gaining increased attention due to both the abundance and importance of this modification across all kingdoms of life. Xylans are a major component of plant cell walls and are the third most abundant biopolymer in Nature. O-Acetyl moieties are the dominant backbone substituents of glucuronoxylan in dicots and play a major role in the polymer-polymer interactions that are crucial for proper wall architecture and normal plant development. Here, we describe the biochemical, structural, and mechanistic characterization of Arabidopsis thaliana xylan O-acetyltransferase 1 (AtXOAT1), a member of the plant-specific Trichome Birefrigence Like (TBL) family that catalyzes the 2-O-acetylation of xylan. A multipronged approach involving X-ray crystallography, biochemical analyses, mutagenesis, and molecular simulations show that XOAT1 catalyzes xylan acetylation through formation of an acyl-enzyme intermediate by a double displacement bi-bi mechanism involving a Ser-His-Asp catalytic triad and unconventionally employs an arginine residue in formation of an oxyanion hole.

biochemistry↗

bioRxiv2018

Determining the link between alpha-gal-containing antigens in North American ticks and red meat allergy

Development of specific IgE antibodies to the oligosaccharide galactose--1, 3-galactose (-gal) following tick bites has been shown to be the source of red meat allergy. In this study, we investigated the presence of -gal in four tick species: the lone-star tick (Amblyomma americanum), the Gulf-Coast tick (Amblyomma maculatum), the American dog tick (Dermacentor variabilis), and the black-legged tick (Ixodes scapularis) by using a combination of immunoproteome, carbohydrate analysis, and basophil activation approaches. Using anti--gal antibodies, -gal was identified in the salivary glands of both Am. americanum and Ix. scapularis, while Am. maculatum and De. variabilis appeared to lack the sugar. PNGase F treatment confirmed the deglycosylation of N-linked -gal-containing proteins in tick salivary glands. Immunolocalization of -gal moieties to the salivary secretory vesicles of the salivary acini also confirmed the secretory nature of -gal-containing antigens in ticks. Am. americanum ticks were fed human blood (lacks -gal) using an artificial membrane feeding system to determine the source of -gal. N-linked glycan analysis revealed that Am. americanum and Ix. scapularis have -gal in their saliva and salivary glands, but Am. maculatum contains no detectable quantity. Salivary samples from Am. americanum and Ix. scapularis stimulated activation of basophils primed with plasma from -gal allergic subjects. Together, our data support the idea that bites from certain tick species may specifically create a risk for the development of -gal-specific IgE and hypersensitivity reactions in humans. Alpha-Gal syndrome challenges the current food allergy paradigm and broadens opportunities for future research.

immunology↗