Current Protein and Peptide Science - Volume 19, Issue 1, 2018

Proteins are one of the most multifaceted macromolecules in living systems. Proteins have evolved to function under physiological conditions and, therefore, are not usually tolerant of harsh experimental and environmental conditions. The growing use of proteins in industrial processes as a greener alternative to chemical catalysts often demands constant innovation to improve their performance. Protein engineering aims to design new proteins or modify the sequence of a protein to create proteins with new or desirable functions. With the emergence of structural and functional genomics, protein engineering has been invigorated in the post-genomic era. The three-dimensional structures of proteins with known functions facilitate protein engineering approaches to design variants with desired properties. There are three major approaches of protein engineering research, namely, directed evolution, rational design, and de novo design. Rational design is an effective method of protein engineering when the threedimensional structure and mechanism of the protein is well known. In contrast, directed evolution does not require extensive information and a three-dimensional structure of the protein of interest. Instead, it involves random mutagenesis and selection to screen enzymes with desired properties. De novo design uses computational protein design algorithms to tailor synthetic proteins by using the three-dimensional structures of natural proteins and their folding rules. The present review highlights and summarizes recent protein engineering approaches, and their challenges and limitations in the post-genomic era.

Bacterial luminescence is the end-product of biochemical reactions catalyzed by the luciferase enzyme. Nowadays, this fascinating phenomenon has been widely used as reporter and/or sensors to detect a variety of biological and environmental processes. The enhancement or diversification of the luciferase activities will increase the versatility of bacterial luminescence. Here, to establish the strategy for luciferase engineering, we summarized the identity and relevant roles of key amino acid residues modulating luciferase in Vibrio harveyi, a model luminous bacterium. The current opinions on crystal structures and the critical amino acid residues involved in the substrate binding sites and unstructured loop have been delineated. Based on these, the potential target residues and/or parameters for enzyme engineering were also suggested in limited scale. In conclusion, even though the accurate knowledge on the bacterial luciferase is yet to be reported, the structure-guided site-directed mutagenesis approaches targeting the regulatory amino acids will provide a useful platform to re-engineer the bacterial luciferase in the future.

Glycosaminoglycans (GAGs) such as chondroitin sulfate (CS) are the chief natural polysaccharides which reside in biological tissues mainly in extracellular matrix. These CS along with adhesion molecules and growth factors are involved in central nervous system (CNS) development, cell progression and pathogenesis. The chondroitin lyases are the enzyme that degrade and alter the CS chains and hence modify various signalling pathways involving CS chains. These CS lyases are substrate specific, can precisely manipulate the CS polysaccharides and have various biotechnological, medical and therapeutic applications. These enzymes can be used to produce the unsaturated oligosaccharides, which have immune-modulatory, anti-inflammatory and neuroprotective properties. This review focuses on the major breakthrough of the chondroitin sulfate degrading enzymes, their structures and functioning mechanism. This also provides comprehensive information regarding production, purification, characterization of CS lyases and their major applications, both established as well as emerging ones such as neural development.

β-mannanases have been shown to play an important role in various biological processes such as the cell wall component degradation, defence signalling in plants, the mobilization of storage reserves and in various industrial processes. To date, glycoside hydrolases (GHs) have been divided into 135 families and 14 clans from A to N based upon their sequence, overall structural fold and function. β -mannanases belong glycoside hydrolases and exist under four different glycoside hydrolase families, GH5, GH26, GH113 and GH134. GH5 and GH26 are combined in clan GH-A. GH5 and GH26 contain hydrolases which follow the retaining type reaction mechanism. Structural survey of β- mannanases of GH5 and GH26, suggests that both families contain similar TIM barrel fold. In addition, they also share common catalytic residues and their location in the structure. Despite these structural similarities, a distinct difference lies between the substrate binding sub-sites which define substrate specificity. This review summarizes the recent reports on the structure and function perspectives of β- mannanases of GH5 and GH26 and highlights the similarities and differences between them.

Xylooligosaccharides (XOS) have gained increased interest as prebiotics during the last years. XOS and arabinoxylooligosaccharides (AXOS) can be produced from major fractions of biomass including agricultural by-products and other low cost raw materials. Endo-xylanases are key enzymes for the production of (A)XOS from xylan. As the xylan structure is broadly diverse due to different substitutions, diverse endo-xylanases have evolved for its degradation. In this review structural and functional aspects are discussed, focusing on the potential applications of endo-xylanases in the production of differently substituted (A)XOS as emerging prebiotics, as well as their implication in the processing of the raw materials. Endo-xylanases are found in at least eight different glycoside hydrolase families (GH), and can either have a retaining or an inverting catalytic mechanism. To date, it is mainly retaining endo-xylanases that are used in applications to produce (A)XOS. Enzymes from these GH-families (mainly GH10 and GH11, and the more recently investigated GH30) are taken as prototypes to discuss substrate preferences and main products obtained. Finally, the need of new and accessory enzymes (new specificities from new families or sources) to increase the yield of different types of (A)XOS is discussed, along with in vitro tests of produced oligosaccharides and production of enzymes in GRAS organisms to facilitate use in functional food manufacturing.

Probiotic supplements in food industry have attracted a lot of attention and shown a remarkable growth in this field. Metabolic engineering (ME) approaches enable understanding their mechanism of action and increases possibility of designing probiotic strains with desired functions. Probiotic microorganisms generally referred as industrially important lactic acid bacteria (LAB) which are involved in fermenting dairy products, food, beverages and produces lactic acid as final product. A number of illustrations of metabolic engineering approaches in industrial probiotic bacteria have been described in this review including transcriptomic studies of Lactobacillus reuteri and improvement in exopolysaccharide (EPS) biosynthesis yield in Lactobacillus casei LC2W. This review summaries various metabolic engineering approaches for exploring metabolic pathways. These approaches enable evaluation of cellular metabolic state and effective editing of microbial genome or introduction of novel enzymes to redirect the carbon fluxes. In addition, various system biology tools such as in silico design commonly used for improving strain performance is also discussed. Finally, we discuss the integration of metabolic engineering and genome profiling which offers a new way to explore metabolic interactions, fluxomics and probiogenomics using probiotic bacteria like Bifidobacterium spp and Lactobacillus spp.

Cytochrome P450 enzymes are a structurally conserved but functionally diverse group of heme-containing mixed function oxidases found across both prokaryotic and eukaryotic forms of the microbial world. Microbial P450s are known to perform diverse functions ranging from the synthesis of cell wall components to xenobiotic/drug metabolism to biodegradation of environmental chemicals. Conventionally, many microbial systems have been reported to mimic mammalian P450-like activation of drugs and were proposed as the in-vitro models of mammalian drug metabolism. Recent reports suggest that native or engineered forms of specific microbial P450s from these and other microbial systems could be employed for desired specific biotransformation reactions toward natural and synthetic (drug) compounds underscoring their emerging potential in drug improvement and discovery. On the other hand, microorganisms particularly fungi and actinomycetes have been shown to possess catabolic P450s with unusual potential to degrade toxic environmental chemicals including persistent organic pollutants (POPs). Wood-rotting basidiomycete fungi in particular have revealed the presence of exceptionally large P450 repertoire (P450ome) in their genomes, majority of which are however orphan (with no known function). Our pre- and post-genomic studies have led to functional characterization of several fungal P450s inducible in response to exposure to several environmental toxicants and demonstration of their potential in bioremediation of these chemicals. This review is an attempt to summarize the postgenomic unveiling of this versatile enzyme superfamily in microbial systems and investigation of their potential to synthesize new drugs and degrade persistent pollutants, among other biotechnological applications.

Xylanases are crucial enzymes to hydrolyse the xylan of plant hemicellulose in order to complete the carbon cycle. Xylanases have been used widely in a variety of industries ranging from food and feed industry to pulp and paper industry. Most of the industrial processes which using xylanase requires a thermostable and alkali stable enzyme. Therefore it is desired to produce high thermostable and alkali stable xylanase with high activity. In this review a number of molecular techniques are used in this genomic era have been utilized to enhance physiological properties of xylanases for greater commercial application in the industries. A brief outline of diverse molecular techniques such as genome-walking PCR, thermal asymmetric interlaced PCR (TAIL-PCR), staggered extension process (StEP) recombination method, site-directed mutagenesis together with metagenomic approaches have been discussed which are used to improve the charactestics of xylanases and its production. Metagenomic studies along with directed evolution by mutant creation have also been reported as an effective tool in improvement of xylanase activity and its properties. This review comprehensively describes the recent reports and different combinatorial approaches towards production of efficient xylanases.

It has been well known that laccases can directly or indirectly catalyze oxidation of a broad species of phenols, amines and many other electron donor substrates. However, laccases as biocatalyst in “green” ionic liquids (ILs) media instead of conventional solvents are less known and regarded as an innovative research direction. The presence of ILs can either inhibit or stimulate laccase activity, strongly depending on water-miscibility and kosmotropic natures of ILs. In addition, enzyme source, mediator, pH as well as water content are very important factors which influence laccase activity and stability. Therefore, elucidation of mechanisms underlying the interactions between laccases and ILs will facilitate to screen ILs with excellent laccase compatibility. Strategies based on molecular evolution, enzyme immobilization and/or ILs modification greatly increase the tolerance of laccases against specific ILs. The use of ILs can spread the laccase applications in fields of biosynthesis, biodegradation, biosensor and biofuel cells. This article summarizes the recent progress, trends and problems in this field and focuses, in particular, on the stimulation of laccase activity in aqueous ILs media.

Virus-like particles (VLPs) are nanoscale biological structures consisting of viral proteins assembled in a morphology that mimic the native virion but do not contain the viral genetic material. The possibility of chemically and genetically modifying the proteins contained within VLPs makes them an attractive system for numerous applications. As viruses are potent immune activators as well as natural delivery vehicles of genetic materials to their host cells, VLPs are especially well suited for antigen and drug delivery applications. Despite the great potential, very few VLP designs have made it through clinical trials. In this review, we will discuss the challenges of developing VLPs for antigen and drug delivery, strategies being explored to address these challenges, and the genetic and chemical approaches available for VLP engineering.