Site-Specific Selenocysteine Incorporation into Proteins by Genetic Engineering

Facile Generation of Cyanoselenocysteine as a Vibrational Label for Measuring Protein Dynamics on Longer Time Scales by 2D IR Spectroscopy

Two-dimensional infrared (2D IR) spectroscopy is a powerful technique for measuring molecular heterogeneity and dynamics with a high spatiotemporal resolution. The methods can be applied to characterize specific residues of proteins by incorporating frequency-resolved vibrational labels. However, the time scale of dynamics that 2D IR spectroscopy can measure is limited by the vibrational label's excited-state lifetime due to the decay of 2D IR absorption bands. To extend this time scale, vibrational labels with longer lifetimes are sought. An effective approach to inhibiting intramolecular energy relaxation is to isolate the vibration from the rest of the molecule by inserting a heavy atom bridge. Although this strategy has been demonstrated through the generation of functionalized amino acids, a straightforward route to their selective incorporation into proteins is often unclear. A facile approach for the attachment of a cyano group at cysteine to generate a thiocyanate has contributed to its adoption as a vibrational label of proteins. We demonstrate that an analogous route can be used for introducing cyanoselenocysteine to generate a selenocyanate vibrational label containing a heavier bridge atom. We confirm by infrared pump-probe and 2D IR spectroscopy longer vibrational lifetimes of 100-250 ps, depending on the solvent, which enable the collection of 2D IR spectra to measure frequency dynamics on longer time scales.

Expanding the Genetic Code of Bioelectrocatalysis and Biomaterials

Genetic code expansion is a promising genetic engineering technology that incorporates noncanonical amino acids into proteins alongside the natural set of 20 amino acids. This enables the precise encoding of non-natural chemical groups in proteins. This review focuses on the applications of genetic code expansion in bioelectrocatalysis and biomaterials. In bioelectrocatalysis, this technique enhances the efficiency and selectivity of bioelectrocatalysts for use in sensors, biofuel cells, and enzymatic electrodes. In biomaterials, incorporating non-natural chemical groups into protein-based polymers facilitates the modification, fine-tuning, or the engineering of new biomaterial properties. The review provides an overview of relevant technologies, discusses applications, and highlights achievements, challenges, and prospects in these fields.

Genetically Encoded Photocaged Proteinogenic and Non-Proteinogenic Amino Acids

Photocaged amino acids could be genetically encoded into proteins via genetic code expansion (GCE) and constitute unique tools for innovative protein engineering. There are a number of photocaged proteinogenic amino acids that allow strategic conversion of proteins into their photocaged variants, thus enabling spatiotemporal and non-invasive regulation of protein functions using light. Meanwhile, there are a hand of photocaged non-proteinogenic amino acids that address the challenges in directly encoding certain non-canonical amino acids (ncAAs) that structurally resemble proteinogenic ones or possess highly reactive functional groups. Herein, we would like to summarize the efforts in encoding photocaged proteinogenic and non-proteinogenic amino acids, hoping to draw more attention to this fruitful and exciting scientific campaign.

Selenium chemistry for spatio-selective peptide and protein functionalization

The ability to construct a peptide or protein in a spatio-specific manner is of great interest for therapeutic and biochemical research. However, the various functional groups present in peptide sequences and the need to perform chemistry under mild and aqueous conditions make selective protein functionalization one of the greatest synthetic challenges. The fascinating paradox of selenium (Se) - being found in both toxic compounds and also harnessed by nature for essential biochemical processes - has inspired the recent exploration of selenium chemistry for site-selective functionalization of peptides and proteins. In this Review, we discuss such approaches, including metal-free and metal-catalysed transformations, as well as traceless chemical modifications. We report their advantages, limitations and applications, as well as future research avenues.

Delivery of the selenoprotein thioredoxin reductase 1 to mammalian cells

Over-expression of genetically encoded thioredoxin reductase 1 (TrxR1) TrxR1 can be toxic to cells due to the formation of a truncated version of the enzyme. We developed a new mammalian cell-based model to investigate TrxR1 activity. Fusion of the HIV-derived cell penetrating peptide (TAT) enabled efficient cellular uptake of purified TrxR1 containing 21 genetically encoded amino acids, including selenocysteine. The TAT peptide did not significantly alter the catalytic activity of TrxR1 in vitro. We monitored TrxR1-dependent redox activity in human cells using a TrxR1-specific red fluorescent live-cell reporter. Using programmed selenocysteine incorporation in Escherichia coli, our approach allowed efficient production of active recombinant human selenoprotein TrxR1 for delivery to the homologous context of the mammalian cell. The delivered TAT-TrxR1 showed robust activity in live cells and provided a novel platform to study TrxR1 biology in human cells.

Reprogramming the Biosynthesis of Precursor Peptide to Create a Selenazole-Containing Nosiheptide Analogue

Nosiheptide (NOS), a potent bactericidal thiopeptide, belongs to a class of natural products produced by ribosomal synthesis and post-translational modifications, and its biosynthetic pathway has largely been elucidated. However, the central trithiazolylpyridine structure of NOS remains inaccessible to structural changes. Here we report the creation of a NOS analogue containing a unique selenazole ring by the construction of an artificial system in Streptomyces actuosus ATCC25421, where the genes responsible for the biosynthesis of selenoprotein from Escherichia coli and the biosynthetic gene cluster of NOS were rationally integrated to produce a selenazole-containing analogue of NOS. The thiazole at the fifth position in NOS was specifically replaced by a selenazole to afford the first selenazole-containing "unnatural" natural product. The present strategy is useful for structural manipulation of various RiPP natural products.