The glycosylation of AGP and its associations with the binding to methadone

OUP accepted manuscript

Glycans expand the structural complexity of proteins by several orders of magnitude, resulting in a tremendous analytical challenge when including them in biomedical research. Recent glycobiological research is painting a picture in which glycans represent a crucial structural and functional component of the majority of proteins, with alternative glycosylation of proteins and lipids being an important regulatory mechanism in many biological and pathological processes. Since interindividual differences in glycosylation are extensive, large studies are needed to map the structures and to understand the role of glycosylation in human (patho)physiology. Driven by these challenges, methods have emerged, which can tackle the complexity of glycosylation in thousands of samples, also known as high-throughput (HT) glycomics. For facile dissemination and implementation of HT glycomics technology, the sample preparation, analysis, as well as data mining, need to be stable over a long period of time (months/years), amenable to automation, and available to non-specialized laboratories. Current HT glycomics methods mainly focus on protein N-glycosylation and allow to extensively characterize this subset of the human glycome in large numbers of various biological samples. The ultimate goal in HT glycomics is to gain better knowledge and understanding of the complete human glycome using methods that are easy to adapt and implement in (basic) biomedical research. Aiming to promote wider use and development of HT glycomics, here, we present currently available, emerging, and prospective methods and some of their applications, revealing a largely unexplored molecular layer of the complexity of life.

N-glycan microheterogeneity regulates interactions of plasma proteins

Glycosylation is one of the most common and complex posttranslation modifications that significantly influences protein structure and function. However, linking individual glycan structures to protein interactions remains challenging and typically requires multiple techniques. Here, we establish a mass-spectrometric approach to systematically dissect the microheterogeneity of two important serum proteins, α1-acid glycoprotein and haptoglobin, and relate glycan features to drug and protein-binding interaction kinetics. We found that the degree of N-glycan branching and extent of terminal fucosylation can attenuate or enhance these interactions, providing important insight into drug transport in plasma. Our study demonstrates an approach capable of investigating how protein glycosylation fine-tunes protein–drug interactions at the glycan-specific level and will prove universally useful for studying glycoprotein interactions.

Altered glycosylation patterns of plasma proteins are associated with autoimmune disorders and pathogenesis of various cancers. Elucidating glycoprotein microheterogeneity and relating subtle changes in the glycan structural repertoire to changes in protein–protein, or protein–small molecule interactions, remains a significant challenge in glycobiology. Here, we apply mass spectrometry-based approaches to elucidate the global and site-specific microheterogeneity of two plasma proteins: α1-acid glycoprotein (AGP) and haptoglobin (Hp). We then determine the dissociation constants of the anticoagulant warfarin to different AGP glycoforms and reveal how subtle N-glycan differences, namely, increased antennae branching and terminal fucosylation, reduce drug-binding affinity. Conversely, similar analysis of the haptoglobin–hemoglobin (Hp–Hb) complex reveals the contrary effects of fucosylation and N-glycan branching on Hp–Hb interactions. Taken together, our results not only elucidate how glycoprotein microheterogeneity regulates protein–drug/protein interactions but also inform the pharmacokinetics of plasma proteins, many of which are drug targets, and whose glycosylation status changes in various disease states.

Tell-Tale SNPs: The Role of CYP2B6 in Methadone Fatalities

Cytochrome P450 (CYP) enzyme 2B6 plays a significant role in the stereo-selective metabolism of (S)-methadone to 2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolidine, an inactive methadone metabolite. Elevated (S)-methadone can cause cardiotoxicity by prolonging the QT interval of the heart's electrical cycle. Large inter-individual variability of methadone pharmacokinetics causes discordance in the relationship between dose, plasma concentrations and side effects. The purpose of this study was to determine if one or more single nucleotide polymorphisms (SNPs) located within the CYP2B6 gene contributes to a poor metabolizer phenotype for methadone in these fatal cases. The genetic analysis was conducted on 125 Caucasian methadone-only fatalities obtained from the West Virginia and Kentucky Offices of the Chief Medical Examiner. The frequency of eight exonic and intronic SNPs (rs2279344, rs3211371, rs3745274, rs4803419, rs8192709, rs8192719, rs12721655 and rs35979566) was determined. The frequencies of SNPs rs3745274 (*9, c516G > T, Q172H), and rs8192719 (21563 C > T) were enhanced in the methadone-only group. Higher blood methadone concentrations were observed in individuals who were genotyped homozygous for SNP rs3211371 (*5, c1459C > T, R487C). These results indicate that these three CYP2B6 SNPs are associated with methadone fatalities.