Protein engineering for covalent immobilization and enhanced stability through incorporation of multiple noncanonical amino acids

In Vitro Selection of Collagen-Binding Vascular Endothelial Growth Factor Containing Genetically Encoded Mussel-Inspired Adhesive Amino Acids

Protein immobilization technology is important in medical and industrial applications. We previously reported all-in-one in vitro selection, wherein a collagen-binding vascular endothelial growth factor (CB-VEGF) was identified from a fusion library of random and VEGF sequences. However, its interaction chemistry is mainly limited to the interaction established by the 20 canonical amino acids. Herein, we incorporated an adhesive non-natural amino acid found in marine mussels, L-3,4-dihydroxyphenylalanine (DOPA), into the library for all-in-one in vitro selection. After selection, we identified DOPA-containing CB-VEGF. CB-VEGF binds to collagen with an apparent dissociation constant of 2 nM; naïve VEGF does not bind to collagen. The collagen-binding peptide domain of CB-VEGF (CB-peptide) exhibited stronger binding to collagen than a mutant peptide (substitution from DOPA to tyrosine), indicating the importance of DOPA to collagen binding. The collagen-binding affinity of CB-VEGF is 10-fold higher than that of CB-peptide, suggesting that the collagen-binding ability of CB-VEGF is not due to the additive function of CB-peptide to VEGF, but is synergistic. Furthermore, increased cell growth was observed on CB-VEGF-treated collagen surfaces, not VEGF-treated collagen surfaces. Thus, integrating all-in-one in vitro selection and DOPA incorporation shows promise in generating adhesive proteins on solid supports.

Non-canonical amino acids as a tool for the thermal stabilization of enzymes

Biocatalysis has become a powerful alternative for green chemistry. Expanding the range of amino acids used in protein biosynthesis can improve industrially appealing properties such as enantioselectivity, activity and stability. This review will specifically delve into the thermal stability improvements that non-canonical amino acids (ncAAs) can confer to enzymes. Methods to achieve this end, such as the use of halogenated ncAAs, selective immobilization and rational design, will be discussed. Additionally, specific enzyme design considerations using ncAAs are discussed along with the benefits and limitations of the various approaches available to enhance the thermal stability of enzymes.

Protein Stability: Enhancement and Measurement

This chapter defines protein stability, emphasizes its importance, and surveys the field of protein stabilization, with summary reference to a selection of 2014-2021 publications. One can enhance stability, particularly by protein engineering strategies but also by chemical modification and by other means. General protocols are set out on how to measure a given protein's (i) kinetic thermal stability and (ii) oxidative stability and (iii) how to undertake chemical modification of a protein in solution.

Beyond protein tagging: Rewiring the genetic code of fluorescent proteins - A review

Fluorescent proteins (FP) are an integral part of modern biology due to its diverse biochemical and photophysical properties. The boundaries of FP have been extended through conventional mutagenesis and directed evolution approaches. Engineering of FP based on the standard genetic code consisting of 20 amino acids with limited functional groups restrict its diversification. Degeneracy of genetic code has helped in covering this substantial gap through genetic code engineering, wherein introduction of unnatural amino acid (UAA) analogues resulted in a collection of FP with varying properties. This review features the work carried till date in the area of FP incorporated with UAAs and explores strategies employed for incorporation, impact of UAAs in chromophore and surrounding residues and changes in inherent properties of FP. The long-standing association of FP as a tool for high throughput screening of orthogonal aaRS/tRNA pairs used in site specific incorporation of UAAs is expounded. Insertion of UAAs in FP has enabled their use in contemporary fields such as biophotovoltaics, bioremediation, biosensors, biomaterials and imaging of acidic vesicles. Thus, expansion of genetic code of FP is envisaged to rejig the existing spectra of colors and future research initiative in this direction is expected to glow brighter and brighter.

Reprogramming natural proteins using unnatural amino acids

Unnatural amino acids have gained significant attention in protein engineering and drug discovery as they allow the evolution of proteins with enhanced stability and activity. The incorporation of unnatural amino acids into proteins offers a rational approach to engineer enzymes for designing efficient biocatalysts that exhibit versatile physicochemical properties and biological functions. This review highlights the biological and synthetic routes of unnatural amino acids to yield a modified protein with altered functionality and their incorporation methods. Unnatural amino acids offer a wide array of applications such as antibody-drug conjugates, probes for change in protein conformation and structure-activity relationships, peptide-based imaging, antimicrobial activities, etc. Besides their emerging applications in fundamental and applied science, systemic research is necessary to explore unnatural amino acids with novel side chains that can address the limitations of natural amino acids.

Chemical modification of enzymes to improve biocatalytic performance

Improvement in intrinsic enzymatic features is in many instances a prerequisite for the scalable applicability of many industrially important biocatalysts. To this end, various strategies of chemical modification of enzymes are maturing and now considered as a distinct way to improve biocatalytic properties. Traditional chemical modification methods utilize reactivities of amine, carboxylic, thiol and other side chains originating from canonical amino acids. On the other hand, noncanonical amino acid- mediated 'click' (bioorthogoal) chemistry and dehydroalanine (Dha)-mediated modifications have emerged as an alternate and promising ways to modify enzymes for functional enhancement. This review discusses the applications of various chemical modification tools that have been directed towards the improvement of functional properties and/or stability of diverse array of biocatalysts.

Robust, site-specifically immobilized phenylalanine ammonia-lyases for the enantioselective ammonia addition of cinnamic acids

Phenylalanine ammonia-lyases (PALs) catalyse the non-oxidative deamination of l-phenylalanine to trans-cinnamic acid, while in the presence of high ammonia concentration, the synthetically attractive reverse reaction occurs. Although they have been intensively studied, the wider application of PALs for the large scale synthesis of non-natural amino acids is still rather limited, mainly due to the decreased operational stability of PALs under the high ammonia concentration conditions of ammonia addition. Herein, we describe the development of a highly stable and active immobilized PAL-biocatalyst obtained through site-specific covalent immobilization onto single-walled carbon nanotubes (SWCNTs), employing maleimide/thiol coupling of engineered enzymes containing surficial Cys residues. The immobilization method afforded robust biocatalysts (by strong covalent attachment to the support) and allowed modulation of enzymatic activity (by proper selection of binding site, controlling the orientation of the enzyme attached to the support). The novel biocatalysts were investigated in PAL-catalyzed reactions, focusing on the synthetically challenging ammonia addition reaction. The optimization of the immobilization (enzyme load) and reaction conditions (substrate : biocatalyst ratio, ammonia source, reaction temperature) involving the best performing biocatalyst SWCNTNH2 -SS-PcPAL was performed. The biocatalyst, under the optimal reaction conditions, showed high catalytic efficiency, providing excellent conversion (c ∼90% in 10 h) of cinnamic acid into l-Phe, and more importantly, possesses high operational stability, maintaining its high efficiency over >7 reaction cycles. Moreover, the site-specifically immobilized PcPAL L134A/S614C and PcPAL I460V/S614C variants were successfully applied in the synthesis of several l-phenylalanine analogues of high synthetic value, providing perspectives for the efficient replacement of classical synthetic methods for l-phenylalanines with a mild, selective and eco-friendly enzymatic alternative.

In vivo biosynthesis of tyrosine analogs and their concurrent incorporation into a residue-specific manner for enzyme engineering

A cellular system for the in vivo biosynthesis of Tyr-analogs and their concurrent incorporation into target proteins is reported.

A facile method for high level dual expression of recombinant and congener protein in a single expression system

Protein engineering is an emerging field for developing novel therapeutic proteins and commercial enzymes, along with a major impact on the global market. In recent decades, advanced methods employing protein modification through expansion of the genetic code have led to the development of proteins with new biochemical and physical properties. These techniques have produced engineered proteins with improved attribute comprising substrate relaxation, protein drug conjugation and high stability under extreme conditions of high temperatures, pH and organic solvents. Furthermore, residue specific incorporation is the simplest method for the global incorporation of non-canonical amino acid (NCAA) for protein modification; however it has the major drawbacks of high production cost and manpower requirement. In the present study, we developed a method for the incorporation of single NCAA in two different proteins by using Escherichia coli (E. coli) expression system. For that, the dual protein expressing Escherichia coli JW2581 strain was constructed by transforming pQE80L and pD881-PpiBT vectors with different promoters, selectable markers and AnnexinV, GFPHS gene. To modify the protein, the 3,4 dihydroxy phenyl alanine (DOPA) was globally incorporated into the GFPHS and Annexin V protein using dual protein expression system. The incorporation efficiency during the dual protein expression was achieved through optimized concentrations of amino acids, carbohydrate and inducers in minimal medium. This method for the incorporation of single NCAA into two different proteins using a single expression host system saves the production cost, manpower and time substantially.

Antimicrobial and Antibiofilm Activity of UP-5, an Ultrashort Antimicrobial Peptide Designed Using Only Arginine and Biphenylalanine

The recent upsurge of multidrug resistant bacteria (MDRB) among global communities has become one of the most serious challenges facing health professionals and the human population worldwide. Cationic ultrashort antimicrobial peptides (USAMPs) are a promising group of molecules that meet the required criteria of novel antimicrobial drug development. UP-5, a novel penta-peptide, displayed significant antimicrobial activities against various standard and clinical isolates of MDRB. UP-5 displayed MICs values within the range of (10–15 μM) and (55–65 μM) against Gram-positive and Gram-negative bacteria, respectively. Furthermore, UP-5 displayed antibiofilm activity with minimum biofilm eradication concentration (MBEC) value as equal to twofold higher than MIC value. At the same inhibitory concentrations, UP-5 exhibited very low or negligible toxicity toward human erythrocytes and mammalian cells. Combining UP-5 with conventional antibiotics led to a synergistic or additive mode of action that resulted in the reduction of the MIC values for some of the antibiotics by 99.7% along a significant drop in MIC values of the peptide. The stability profile of UP-5 was evaluated in full mouse plasma and serum with results indicating a more stable pattern in plasma. The present study indicates that USAMPs are promising antimicrobial agents that can avoid the negative characteristics of conventional antimicrobial peptides. Additionally, USAMPs exhibit good to moderate activity against MDRB, negligible toxicity, and synergistic outcomes in combination with conventional antimicrobial agents.