Hydrogel spheres, fashioned from an operationally simple mould, that incorporate boronate units were shown to function as saccharide sensors.

The incorporation of the specialized carbohydrate affinity ligand methacrylamido phenylboronic acid in polyacrylamide gels for SDS-PAGE analysis has been successful for the separation of carbohydrates and has here been adapted for the analysis of post-translationally modified proteins. While conventional SDS-PAGE analysis cannot distinguish between glycated and unglycated proteins, methacrylamido phenylboronate acrylamide gel electrophoresis (mP-AGE) in low loading shows dramatic retention of delta-gluconolactone modified proteins, while the mobility of the unmodified proteins remains unchanged. With gels containing 1% methacrylamido phenylboronate, mP-AGE analysis of gluconoylated recombinant protein Sbi results in the retention of the modified protein at a position expected for a protein that has quadrupled its expected molecular size. Subsequently, mP-AGE was tested on HSA, a protein that is known to undergo glycation under physiological conditions. mP-AGE could distinguish between various carbohydrate-protein adducts, using in vitro glycated HSA, and discriminate early from late glycation states of the protein. Enzymatically glycosylated proteins show no altered retention in the phenylboronate-incorporated gels, rendering this method highly selective for glycated proteins. We reveal that a trident interaction between phenylboronate and the Amadori cis 1,2 diol and amine group provides the molecular basis of this specificity. These results epitomize mP-AGE as an important new proteomics tool for the detection, separation, visualization and identification of protein glycation. This method will aid the design of inhibitors of unwanted carbohydrate modifications in recombinant protein production, ageing, diabetes, cardiovascular diseases and Alzheimer's disease.

Glucose and glucose metabolites are able to adversely modify proteins through a non-enzymatic reaction called glycation, which is associated with the pathology of Alzheimer’s Disease (AD) and is a characteristic of the hyperglycaemia induced by diabetes. However, the precise protein glycation profile that characterises AD is poorly defined and the molecular link between hyperglycaemia and AD is unknown. In this study, we define an early glycation profile of human brain using fluorescent phenylboronate gel electrophoresis and identify early glycation and oxidation of macrophage migration inhibitory factor (MIF) in AD brain. This modification inhibits MIF enzyme activity and ability to stimulate glial cells. MIF is involved in immune response and insulin regulation, hyperglycaemia, oxidative stress and glycation are all implicated in AD. Our study indicates that glucose modified and oxidised MIF could be a molecular link between hyperglycaemia and the dysregulation of the innate immune system in AD.

Synthetic receptors for diols that incorporate boronic acid motifs have been developed as new sensors and separation tools. Utilizing the reversible interactions of diols with boronic acids to form boronic esters under new binding regimes has provided new hydrogel constructs that have found use as dye-displacement sensors and electrophoretic separation tools; similarly, molecular boronic-acid-containing chemosensors were constructed that offer applications in the sensing of diols. This review provides a somewhat-personal perspective of developments in boronic-acid-mediated sensing and separation, placed in the context of the seminal works of others in the area, as well as offering a concise summary of the contributions of the co-authors in the area.

Glycated proteins are important biomarkers for age-related disorders, however their analysis is challenging because of the complexity of the protein-carbohydrate adducts. Here we report a method that enables the detection and identification of individual glycated proteins in complex samples using fluorescent boronic acids in gel electrophoresis. Using this method we identified glycated proteins in human serum, insect hemolymph and mouse brain homogenates, confirming this technique as a powerful proteomics tool that can be used for the identification of potential disease biomarkers.