No abstract

Chemical modification of proteins is a rapidly expanding area in chemical biology. Selective installation of biochemical probes has led to a better understanding of natural protein modification and macromolecular function. In other cases such chemical alterations have changed the protein function entirely. Additionally, tethering therapeutic cargo to proteins has proven invaluable in campaigns against disease. For controlled, selective access to such modified proteins, a unique chemical handle is required. Cysteine, with its unique reactivity, has long been used for such modifications. Cysteine has enjoyed widespread use in selective protein modification, yet new applications and even new reactions continue to emerge. This Focus Review highlights the enduring utility of cysteine in protein modification with special focus on recent innovations in chemistry and biology associated with such modifications.

Glycosylation is a key mechanism for orchestrating the bioactivity, metabolism and location of small molecules in living cells. In plants, a large multigene family of glycosyltransferases is involved in these processes, conjugating hormones, secondary metabolites, biotic and abiotic environmental toxins, to impact directly on cellular homeostasis. The red grape enzyme UDP-glucose:flavonoid 3-Oglycosyltransferase (VvGT1) is responsible for the formation of anthocyanins, the health-promoting compounds which, in planta, function as colourants determining flower and fruit colour and are precursors for the formation of pigmented polymers in red wine. We show that VvGT1 is active, in vitro, on a range of flavonoids. VvGT1 is somewhat promiscuous with respect to donor sugar specificity as dissected through full kinetics on a panel of nine sugar donors. The three-dimensional structure of VvGT1 has also been determined, both in its 'Michaelis' complex with a UDP-glucose-derived donor and the acceptor kaempferol and in complex with UDP and quercetin. These structures, in tandem with kinetic dissection of activity, provide the foundation for understanding the mechanism of these enzymes in small molecule homeostasis.

This review rationalizes the varied designs of systems for incorporation of UAAs into proteins via canonical codons.