Enzymatic glycosylation involving fluorinated carbohydrates.

Fluorinated carbohydrates, where one (or more) fluorine atom(s) have been introduced into a carbohydrate structure, typically through deoxyfluorination chemistry, have a wide range of applications in the glycosciences. Fluorinated derivatives of galactose, glucose, N-acetylgalactosamine, N-acetylglucosamine, talose, fucose and sialic acid have been employed as either donor or acceptor substrates in glycosylation reactions. Fluorinated donors can be synthesised by synthetic methods or produced enzymatically from chemically fluorinated sugars. The latter process is mediated by enzymes such as kinases, phosphorylases and nucleotidyltransferases. Fluorinated donors produced by either method can subsequently be used in glycosylation reactions mediated by glycosyltransferases, or phosphorylases yielding fluorinated oligosaccharide or glycoconjugate products. Fluorinated acceptor substrates are typically synthesised chemically. Glycosyltransferases are most commonly used in conjunction with natural donors to further elaborate fluorinated acceptor substrates. Glycoside hydrolases are used with either fluorinated donors or acceptors. The activity of enzymes towards fluorinated sugars is often lower than towards the natural sugar substrates irrespective of donor or acceptor. This may be in part attributed to elimination of the contribution of the hydroxyl group to the binding of the substrate to enzymes. However, in many cases, enzymes still maintain a significant activity, and reactions may be optimised where necessary, enabling enzymes to be used more successfully in the production of fluorinated carbohydrates. This review describes the current state of the art regarding chemoenzymatic production of fluorinated carbohydrates, focusing specifically on examples of the enzymatic production of activated fluorinated donors and enzymatic glycosylation involving fluorinated sugars as either glycosyl donors or acceptors.

The effects of sarcolipin over-expression in mouse skeletal muscle on metabolic activity.

Studies in sarcolipin knockout mice have led to the suggestion that skeletal muscle sarcolipin plays a role in thermogenesis. The mechanism proposed is uncoupling of the sarcoplasmic reticulum calcium pump. However, in other work sarcolipin was not detected in mouse skeletal tissue. We have therefore measured sarcolipin levels in mouse skeletal muscle using semi-quantitative western blotting and synthetic mouse sarcolipin. Sarcolipin levels were so low that it is unlikely that knocking out sarcolipin would have a measurable effect on thermogenesis by SERCA. In addition, overexpression of neither wild type nor FLAG-tagged variants of mouse sarcolipin in transgenic mice had any major significant effects on body mass, energy expenditure, even when mice were fed on a high fat diet.

Introducing affinity and selectivity into galectin-targeting nanoparticles with fluorinated glycan ligands.

Galectins are potential biomarkers and therapeutic targets. However, galectins display broad affinity towards ß-galactosides meaning glycan-based (nano)biosensors lack the required selectivity and affinity. Using a polymer-stabilized nanoparticle biosensing platform, we herein demonstrate that the specificity of immobilised lacto-N-biose towards galectins can be 'turned on/off' by using site-specific glycan fluorination and in some cases reversal of specificity can be achieved. The panel of fluoro-glycans were obtained by a chemoenzymatic approach, exploiting BiGalK and BiGalHexNAcP enzymes from Bifidobacterium infantis which are shown to tolerate fluorinated glycans, introducing structural diversity which would be very laborious by chemical methods alone. These results demonstrate that integrating non-natural, fluorinated glycans into nanomaterials can encode unprecedented selectivity with potential applications in biosensing.

Bifunctional crosslinking ligands for transthyretin.

Wild-type and variant forms of transthyretin (TTR), a normal plasma protein, are amyloidogenic and can be deposited in the tissues as amyloid fibrils causing acquired and hereditary systemic TTR amyloidosis, a debilitating and usually fatal disease. Reduction in the abundance of amyloid fibril precursor proteins arrests amyloid deposition and halts disease progression in all forms of amyloidosis including TTR type. Our previous demonstration that circulating serum amyloid P component (SAP) is efficiently depleted by administration of a specific small molecule ligand compound, that non-covalently crosslinks pairs of SAP molecules, suggested that TTR may be also amenable to this approach. We first confirmed that chemically crosslinked human TTR is rapidly cleared from the circulation in mice. In order to crosslink pairs of TTR molecules, promote their accelerated clearance and thus therapeutically deplete plasma TTR, we prepared a range of bivalent specific ligands for the thyroxine binding sites of TTR. Non-covalently bound human TTR-ligand complexes were formed that were stable in vitro and in vivo, but they were not cleared from the plasma of mice in vivo more rapidly than native uncomplexed TTR. Therapeutic depletion of circulating TTR will require additional mechanisms.