Analysis of the five glycosylation sites of human α1-acid glycoprotein

Abstract

Orosomucoid (OMD) contains complex bi-, tri- and tetra-antennary glycan chains. Subfractionation of OMD into three molecular variants using concanavalin A lectin chromatography is based on variations in these complex structures. Standard h.p.l.c. profiles have been developed to analyse the percentage and distribution of the glycoforms present at each glycosylation site in OMD and its molecular variants. The ability to quantify the glycoforms present at each site allows us to extend the earlier results of others and resolve the remaining questions concerning the glycan structures of these variants. Most significantly, the proportions of bi-, tri- and tetra-antennary chains differ at each site for the three molecular variants. The most strongly retained variant from concanavalin A is uniquely capable of possessing biantennary chains at all five sites, whereas the unretained variant is completely devoid of biantennary chains. Only glycosylation site II of the five present is 100% biantennary in the retained and weakly retained variants. In addition, the two gene products of OMD were differentially glycosylated. Molecular masses of the glycoforms were verified by matrix-assisted u.v. laser desorption mass spectrometry. On the basis of the site distribution of oligosaccharides in the variants, efforts were made to understand the factors that control the processing of the carbohydrate chains in OMD. The results indicate that the 'site-directed' model of processing offers the most consistent explanation for the structures seen at the individual glycosylation sites of OMD.

Glycoprotein analysis of porcine bronchoalveolar lavage fluid reveals potential biomarkers corresponding to resistance toActinobacillus pleuropneumoniaeinfection

“…This protein carries an extensive number of glycan residues which can be differently processed during the posttranslational protein maturation leading to a manifold functional diversity [14]. Former studies described that these modifications can also result in an altered affinity towards the lectin Concanavalin A [45]. Based on this fact, a higher presence of alpha-1-acid glycoprotein in the acute stage of infection cannot be excluded because the lectin-based glycoprotein purification of BALF possibly might hamper the detection of modified versions of this protein.…”

Growth of Streptococcus pneumoniae on Human Glycoconjugates Is Dependent upon the Sequential Activity of Bacterial Exoglycosidases

“…To determine whether S. pneumoniae can utilize monosaccharides liberated from glycoconjugates via exoglycosidase activity, we selected the model glycoprotein, purified human AGP, as a substrate for pneumococcal growth. Human AGP is a well-characterized serum glycoprotein with an average of 16 glycan branches per molecule (38). Although not present in the airway, AGP exhibits the same complex N-linked glycan structure as host defense molecules, which have been previously demonstrated to coat the pneumococcal surface in vivo.…”

A meta-analysis of genome-wide association studies identifies ORM1 as a novel gene controlling thrombin generation potential

“…Finally, in vitro functional studies revealed that plasma orosomucoid levels correlate with lag time and that supplementing the plasma of healthy individuals with orosomucoid resulted in impaired thrombin activity as characterized by increased lag time; this observation being consistent with the concomitant associations of rs150611042-A allele with both decreased lag time and decreased ORM1 expression. ORM1 encodes a key acute phase plasma protein, orosomucoid also called a-1-acid glycoprotein 1 (a-1-AGP) 55 whose specific function has not yet been determined; it might function as a transport protein in the blood stream, appears to modulate the immune system during the acute-phase reaction and has been shown to associate with allergic contact dermatitis, psoriasis, and sarcoidosis. 56 Several pieces of evidence support a role of a-1-AGP in coagulation.…”