Design of protein congeners containing β-cyclopropylalanine

Engineering Pyrrolysyl-tRNA Synthetase for the Incorporation of Non-Canonical Amino Acids with Smaller Side Chains

Site-specific incorporation of non-canonical amino acids (ncAAs) into proteins has emerged as a universal tool for systems bioengineering at the interface of chemistry, biology, and technology. The diversification of the repertoire of the genetic code has been achieved for amino acids with long and/or bulky side chains equipped with various bioorthogonal tags and useful spectral probes. Although ncAAs with relatively small side chains and similar properties are of great interest to biophysics, cell biology, and biomaterial science, they can rarely be incorporated into proteins. To address this gap, we report the engineering of PylRS variants capable of incorporating an entire library of aliphatic "small-tag" ncAAs. In particular, we performed mutational studies of a specific PylRS, designed to incorporate the shortest non-bulky ncAA (S-allyl-l-cysteine) possible to date and based on this knowledge incorporated aliphatic ncAA derivatives. In this way, we have not only increased the number of translationally active "small-tag" ncAAs, but also determined key residues responsible for maintaining orthogonality, while engineering the PylRS for these interesting substrates. Based on the known plasticity of PylRS toward different substrates, our approach further expands the reassignment capacities of this enzyme toward aliphatic amino acids with smaller side chains endowed with valuable functionalities.

In-Cell Synthesis of Bioorthogonal Alkene Tag S-Allyl-Homocysteine and Its Coupling with Reprogrammed Translation

In this study, we report our initial results on in situ biosynthesis of S-allyl-l-homocysteine (Sahc) by simple metabolic conversion of allyl mercaptan in Escherichia coli, which served as the host organism endowed with a direct sulfhydration pathway. The intracellular synthesis we describe in this study is coupled with the direct incorporation of Sahc into proteins in response to methionine codons. Together with O-acetyl-homoserine, allyl mercaptan was added to the growth medium, followed by uptake and intracellular reaction to give Sahc. Our protocol efficiently combined the in vivo synthesis of Sahc via metabolic engineering with reprogrammed translation, without the need for a major change in the protein biosynthesis machinery. Although the system needs further optimisation to achieve greater intracellular Sahc production for complete protein labelling, we demonstrated its functional versatility for photo-induced thiol-ene coupling and the recently developed phosphonamidate conjugation reaction. Importantly, deprotection of Sahc leads to homocysteine-containing proteins-a potentially useful approach for the selective labelling of thiols with high relevance in various medical settings.

Biomimetic strategies to design metallic proteins for detoxification of hazardous heavy metal

Discharge of hazardous heavy metals in to the environment poses a serious threat to the ecosystem owing to its non-degradability and indestructability. Physical and chemical techniques for the removal of heavy metals from industrial effluent is expensive and causes secondary pollution. On the other hand, biological processes using microorganisms play a vital role due to their large surface area to volume ratio, which increases the interactions with metal ions present in the environment. Here, we developed a third generation biological tool for the removal of heavy metal (copper) from the effluent through the biosynthesis of intracellular and surface displayed metallic proteins with novel metal co-ordination chemistry. We evaluated the cell viability for maximum heavy metal adsorption and metal tolerance of synthesized congener metallic proteins. Finally, to eliminate the cost associated with incorporation of metal binding aminoacid, we have introduced a genetic circuit in order to evolve a novel magnetotactic bacterium. The bioreactor studies of the consortia of metallic protein expressing cells immobilized on functionalized granular activated carbon revealed that 97% of copper was adsorbed from the industrial effluent. It is evident that the use of congener metallic proteins will be a futuristic approach for the treatment of wastewater facilitating environmental detoxification.