Site specific biotinylation of the human aldo/keto reductase AKR1A1 for immobilization

From Protein Features to Sensing Surfaces

Proteins play a major role in biosensors in which they provide catalytic activity and specificity in molecular recognition. However, the immobilization process is far from straightforward as it often affects the protein functionality. Extensive interaction of the protein with the surface or significant surface crowding can lead to changes in the mobility and conformation of the protein structure. This review will provide insights as to how an analysis of the physico-chemical features of the protein surface before the immobilization process can help to identify the optimal immobilization approach. Such an analysis can help to preserve the functionality of the protein when on a biosensor surface.

Bioconjugation of green fluorescent protein via an unexpectedly stable cyclic sulfonium intermediate

Smooth converter: Bioconjugation of superfolder GFP involving the formation of an unusually stable, and unprecedented, cyclic sulfonium species is described. This sulfonium can undergo smooth reaction with a range of nucleophiles to give sulfur-, selenium- and azide-modified GFP derivatives in high conversions.

Asborin inhibits Aldo/Keto reductase 1A1

Asborin is the carbaborane analogue of aspirin. Replacement of the phenyl ring in aspirin by ortho-carbaborane was found to change the pharmacological profile of the compound remarkably. Unlike aspirin, asborin cannot selectively acetylate a single serine residue in the active site of cyclooxygenase, and as a result inhibitory potency is reduced. Activation of the acetyl group and the presence of the hydrophobic and bulky cluster therefore did not meet the requirements for cyclooxygenase inhibition. Both features, however, match perfectly for inhibition of the aldo/keto reductase family. Herein, we describe the identification of aldo/keto reductase (AKR) 1A1 as an enzymatic target of asborin, which is inhibited in the low micromolar range. The detailed mode of inhibition was studied and is discussed with respect to the cluster properties. The results shed light on how ortho-carbaborane can be used as a drug synthon, as well as on the development of carbaborane-based inhibitors of other aldo/keto reductases.

Specifically Immobilised Aldo/Keto Reductase AKR1A1 Shows a Dramatic Increase in Activity Relative to the Randomly Immobilised Enzyme

The difference between site-specific and random immobilisation of the aldo/keto reductase AKR1A1 was explored. AKR1A1 was recombinantly expressed as a thioester by the intein strategy. The thioester was selectively modified with a biotin label by the expressed protein ligation method, and subsequent immobilisation on streptavidin templates was performed. Adsorption of wild-type AKR1A1 to streptavidin templates and of biotinylated AKR1A1 to uncoated templates was used to study randomly immobilised enzymes. Investigation of the kinetic parameters revealed remarkably improved activity for the site-specifically immobilised enzyme, which was comparable to that of the wild-type enzyme in solution and 60-300-fold greater than that of the randomly immobilized enzymes. Furthermore, the enzyme was surprisingly stable. No loss of activity was observed for over a week, and even after 50 days more than 35% of activity was maintained.