Site-directed mutagenesis

Design and Production of a Novel Anti-PD-1 Nanobody by CDR Grafting and Site-Directed Mutagenesis Approach

Programmed cell death protein-1 (PD-1) is a membrane protein expressed on the surface of activated T-cells, B-cells, natural killer cells, dendritic cells, macrophages, and monocytes. Inhibition of the PD-1/PD-L1 interaction by monoclonal antibodies (mAbs) has many therapeutic benefits and has led to a major advance in the treatment of various types of tumors. Due to the large size and immunogenicity of the antibodies (Abs), using small molecules such as nanobodies (nanobodies or VHH) is more appropriate for this purpose. In this research, the complementarity determining regions (CDR) grafting method was used to produce anti-PD-1 nanobody. For producing the grafted anti-PD-1 nanobody, CDRs from the tislelizumab mAb were grafted into the frameworks of a nanobody whose sequence is similar to the tislelizumab mAb. Also, the site-directed mutagenesis method was used to produce two mutated anti-PD-1 nanobodies which increased the affinity of grafted anti-PD-1 nanobodies. Two amino acid substitutions (Tyr97Arg and Tyr102Arg) in the VHH-CDR3 were used to improve grafted nanobody affinity and the binding capacity of the mutated nanobodies. The binding of the anti-PD-1 nanobodies and PD-1 antigen (Ag) was confirmed by Dot blot, western blot, and indirect ELISA analysis. According to the results of these in silico and in vitro studies, the binding between grafted and mutated nanobodies with PD-1 was confirmed. Also, our findings show that site-directed mutagenesis can increase the affinity of nanobodies.

Engineering cytokine therapeutics

Cytokines have pivotal roles in immunity, making them attractive as therapeutics for a variety of immune-related disorders. However, the widespread clinical use of cytokines has been limited by their short blood half-lives and severe side effects caused by low specificity and unfavourable biodistribution. Innovations in bioengineering have aided in advancing our knowledge of cytokine biology and yielded new technologies for cytokine engineering. In this Review, we discuss how the development of bioanalytical methods, such as sequencing and high-resolution imaging combined with genetic techniques, have facilitated a better understanding of cytokine biology. We then present an overview of therapeutics arising from cytokine re-engineering, targeting and delivery, mRNA therapeutics and cell therapy. We also highlight the application of these strategies to adjust the immunological imbalance in different immune-mediated disorders, including cancer, infection and autoimmune diseases. Finally, we look ahead to the hurdles that must be overcome before cytokine therapeutics can live up to their full potential.

Enzyme activity engineering based on sequence co-evolution analysis

The utility of engineering enzyme activity is expanding with the development of biotechnology. Conventional methods have limited applicability as they require high-throughput screening or three-dimensional structures to direct target residues of activity control. An alternative method uses sequence evolution of natural selection. A repertoire of mutations was selected for fine-tuning enzyme activities to adapt to varying environments during the evolution. Here, we devised a strategy called sequence co-evolutionary analysis to control the efficiency of enzyme reactions (SCANEER), which scans the evolution of protein sequences and direct mutation strategy to improve enzyme activity. We hypothesized that amino acid pairs for various enzyme activity were encoded in the evolutionary history of protein sequences, whereas loss-of-function mutations were avoided since those are depleted during the evolution. SCANEER successfully predicted the enzyme activities of beta-lactamase and aminoglycoside 3'-phosphotransferase. SCANEER was further experimentally validated to control the activities of three different enzymes of great interest in chemical production: cis-aconitate decarboxylase, α-ketoglutaric semialdehyde dehydrogenase, and inositol oxygenase. Activity-enhancing mutations that improve substrate-binding affinity or turnover rate were found at sites distal from known active sites or ligand-binding pockets. We provide SCANEER to control desired enzyme activity through a user-friendly webserver.

Thermostability engineering of industrial enzymes through structure modification

Thermostability is an essential requirement of enzymes in the industrial processes to catalyze the reactions at high temperatures; thus, enzyme engineering through directed evolution, semi-rational design and rational design are commonly employed to construct desired thermostable mutants. Several strategies are implemented to fulfill enzymes' thermostability demand including decreasing the entropy of the unfolded state through substitutions Gly → Xxx or Xxx → Pro, hydrogen bond, salt bridge, introducing two different simultaneous interactions through single mutant, hydrophobic interaction, filling the hydrophobic cavity core, decreasing surface hydrophobicity, truncating loop, aromatic-aromatic interaction and introducing positively charged residues to enzyme surface. In the current review, horizons about compatibility between secondary structures and substitutions at preferable structural positions to generate the most desirable thermostability in industrial enzymes are broadened. KEY POINTS: • Protein engineering is a powerful tool for generating thermostable industrial enzymes. • Directed evolution and rational design are practical approaches in enzyme engineering. • Substitutions in preferable structural positions can increase thermostability.

Use of Mutagenesis and Functional Screens to Characterize Essential Genes Involved in Lipopolysaccharide Transport

Structure-function analysis is a powerful strategy to characterize the contribution of specific residues to the biogenesis and function of a protein. This approach requires the characterization of strains that express mutant alleles in the absence of the wild-type protein. When studying nonessential bacterial genes, collections of mutants can be easily constructed by introducing plasmid-encoded alleles of interest into a strain that already lacks the wild-type gene. However, this high-throughput approach is not applicable to studying essential genes since their respective null strains are not viable. While there are several tools currently available to modify essential genes, they can be greatly limited by the amount of effort it takes to build and analyze each mutant strain. Here, we describe a high-throughput system for the rapid structure-function analysis of essential genes involved in lipopolysaccharide transport in Escherichia coli. This method, which can be applied to study any essential gene, relies on the initial construction of a single bacterial strain that can be used to generate and functionally characterize multiple plasmid-encoded alleles in under 24 h. We will discuss the advantages and possible shortcomings of our protocol in comparison to other commonly used methods.

Total Syntheses and Chemical Biology Studies of Hymeglusin and Fusarilactone A, Novel Circumventors of β-Lactam Drug Resistance in Methicillin-Resistant Staphylococcus aureus

Hymeglusin, a previously known eukaryotic hydroxymethylglutaryl-CoA (HMG-CoA) synthase inhibitor, was identified as circumventing the β-lactam drug resistance in methicillin-resistant Staphylococcus aureus (MRSA). We describe the concise total syntheses of a series of natural products, which enabled determination of the absolute configuration of fusarilactone A and provided structure-activity relationship information. Based on previous reports, we speculated that the target protein of this circumventing effect may be MRSA bacterial HMG-CoA synthase (mvaS). We found that this enzyme was dose-dependently inhibited by hymeglusin. Furthermore, overexpression of the MRSA mvaS gene and site-directed mutagenesis studies suggested its binding site and the mechanism of action.

Evolution of strept(avidin)-based artificial metalloenzymes in organometallic catalysis

Artificial metalloenzymes have been recently established as efficient alternatives to traditional transition metal catalysts. The presence of a secondary coordination sphere in artificial metalloenzymes makes them advantageous over transition metal catalysts, which rely essentially on their first coordination sphere to exhibit their catalytic activity. Recent developments on streptavidin- and avidin-based artificial metalloenzymes have made them highly chemically and genetically evolved for selective organometallic transformations. In this review, we discuss the chemo-genetic optimization of streptavidin- and avidin-based artificial metalloenzymes for the enhancement of their catalytic activities towards a wide range of synthetic transformations. Considering the high impact in vivo applications of artificial metalloenzymes, their catalytic efficacies to promote abiological reactions in intracellular as well as periplasmic environment are also discussed. Overall, this review can provide an insight to readers regarding the design and systematic optimization of strept(avidin)-based artificial metalloenzymes for specific reactions.

Glutamine-walking: Creating reactive substrates for transglutaminase-mediated protein labeling

Chemically modified proteins are increasingly being tested and approved as therapeutic products. Batch-to-batch homogeneity is crucial to ensure safety and quality of therapeutic products. Highly selective protein modification may be achieved using enzymatic routes. Microbial transglutaminase (mTG) is a robust, easy to use and well-established enzyme that is used at a very large scale in the food industry such that its efficacy and its safety for human consumption are well established. In the context of therapeutic protein modification, mTG should crosslink one or more glutamines on the target protein with an aminated moiety such as a solubilizer, a tracer or a cytotoxic moiety. mTG has the advantage of being unreactive toward the majority of surface-exposed glutamines on most proteins, reducing sample heterogeneity. The caveat is that there may be no reactive glutamine on the target protein, or else a reactive glutamine may be found in a location where its modification compromises function of the target protein. Here we describe the glutamine-walk (Gln-walk), a straightforward method to create a glutamine-substrate site that is reactive to mTG in a target protein. Iterative substitution of single amino acids to a glutamine is followed by facile identification of reactivity with mTG, where covalent labeling of the target with an aminated fluorophore allows visualization of the most reactive modified targets. The approach is empirical; knowledge of the target protein structure and functional regions facilitates application of the method.

The conserved metalloprotease invadolysin is present in invertebrate haemolymph and vertebrate blood

We identified invadolysin, a novel essential metalloprotease, for functions in chromosome structure, cell proliferation and migration. Invadolysin also plays an important metabolic role in insulin signalling and is the only protease known to localise to lipid droplets, the main lipid storage organelle in the cell. In silico examination of the protein sequence of invadolysin predicts not only protease and lipase catalytic motifs, but also post-translational modifications and the secretion of invadolysin. Here we show that the protease motif of invadolysin is important for its role in lipid accumulation, but not in glycogen accumulation. The lipase motif does not appear to be functionally important for the accumulation of lipids or glycogen. Post-translational modifications likely contribute to modulating the level, localisation or activity of invadolysin. We identified a secreted form of invadolysin in the soluble fraction of invertebrate hemolymph (where we observe sexually dimorphic forms) and also vertebrate plasma, including in the extracellular vesicle fraction. Biochemical analysis for various post-translational modifications demonstrated that secreted invadolysin is both N- and O-glycosylated, but not apparently GPI-linked. The discovery of invadolysin in the extracellular milieu suggests a role for invadolysin in normal organismal physiology.

Summary: In this study, we show that the conserved metalloprotease invadolysin is present in invertebrate hemolymph and vertebrate blood, suggesting the protein may function in organismal physiology.

MicroRNA‑373 exerts anti‑tumor functions in human liver cancer by targeting Rab22a

Liver cancer is a one of the most frequent types of tumor worldwide. It has long been recognized that microRNAs are important participants in the progression of various types of cancer. The present study explored the role of microRNA‑373 (miR‑373) in liver cancer development. Reverse transcription‑quantitative polymerase chain reaction was performed to evaluate the transcription level of miR‑373 in 96 liver cancer tissues and adjacent normal liver tissues. The association of miR‑373 with clinicopathological characteristics was analyzed using the χ2 test. Kaplan‑Meier univariate analysis and multivariate hazard analysis were performed to identify the clinical potential of miR‑373 in the prognosis of liver cancer patients. Transfection of miR‑373 mimics into Hep3B and HepG2 liver cancer cell lines was conducted to reveal the underlying mechanism in regulating liver cancer progression. The functional assays included proliferation, migration, invasion and luciferase assays. The findings of the present study demonstrated that miR‑373 transcription level was markedly downregulated in liver cancer tissues compared with the adjacent normal tissues and was associated with the clinical prognosis of liver cancer patients. Overexpressing miR‑373 mimics in liver cancer cell lines decreased cell proliferation and invasion, suggesting that miR‑373 exerts anti‑tumor effects in liver cancer. In addition, data from the present study demonstrated the direct effect of miR373 on inhibiting the expression and signaling of Ras‑related protein Rab22a, a well‑known oncoprotein. Taken together, the results from the present study suggested that miR‑373 suppresses liver cancer progression and may serve as a promising prognosis prediction biomarker.

Four Challenges for Better Biocatalysts

Biocatalysis (the use of biological molecules or materials to catalyse chemical reactions) has considerable potential. The use of biological molecules as catalysts enables new and more specific syntheses. It also meets many of the core principles of “green chemistry”. While there have been some considerable successes in biocatalysis, the full potential has yet to be realised. This results, partly, from some key challenges in understanding the fundamental biochemistry of enzymes. This review summarises four of these challenges: the need to understand protein folding, the need for a qualitative understanding of the hydrophobic effect, the need to understand and quantify the effects of organic solvents on biomolecules and the need for a deep understanding of enzymatic catalysis. If these challenges were addressed, then the number of successful biocatalysis projects is likely to increase. It would enable accurate prediction of protein structures, and the effects of changes in sequence or solution conditions on these structures. We would be better able to predict how substrates bind and are transformed into products, again leading to better enzyme engineering. Most significantly, it may enable the de novo design of enzymes to catalyse specific reactions.

Cognizance of Molecular Methods for the Generation of Mutagenic Phage Display Antibody Libraries for Affinity Maturation

Antibodies leverage on their unique architecture to bind with an array of antigens. The strength of interaction has a direct relation to the affinity of the antibodies towards the antigen. In vivo affinity maturation is performed through multiple rounds of somatic hypermutation and selection in the germinal centre. This unique process involves intricate sequence rearrangements at the gene level via molecular mechanisms. The emergence of in vitro display technologies, mainly phage display and recombinant DNA technology, has helped revolutionize the way antibody improvements are being carried out in the laboratory. The adaptation of molecular approaches in vitro to replicate the in vivo processes has allowed for improvements in the way recombinant antibodies are designed and tuned. Combinatorial libraries, consisting of a myriad of possible antibodies, are capable of replicating the diversity of the natural human antibody repertoire. The isolation of target-specific antibodies with specific affinity characteristics can also be accomplished through modification of stringent protocols. Despite the ability to screen and select for high-affinity binders, some 'fine tuning' may be required to enhance antibody binding in terms of its affinity. This review will provide a brief account of phage display technology used for antibody generation followed by a summary of different combinatorial library characteristics. The review will focus on available strategies, which include molecular approaches, next generation sequencing, and in silico approaches used for antibody affinity maturation in both therapeutic and diagnostic applications.

Parallel molecular evolution and adaptation in viruses

Parallel molecular evolution is the independent evolution of the same genotype or phenotype from distinct ancestors. The simple genomes and rapid evolution of many viruses mean they are useful model systems for studying parallel evolution by natural selection. Parallel adaptation occurs in the context of several viral behaviours, including cross-species transmission, drug resistance, and host immune escape, and its existence suggests that at least some aspects of virus evolution and emergence are repeatable and predictable. We introduce examples of virus parallel evolution and summarise key concepts. We outline the difficulties in detecting parallel adaptation using virus genomes, with a particular focus on phylogenetic and structural approaches, and we discuss future approaches that may improve our understanding of the phenomenon.

Mechanical Softening of a Small Ubiquitin-Related Modifier Protein Due to Temperature Induced Flexibility at the Core

Despite the growing interest in the thermal softening of proteins, the mechanistic details of it are far from understood. β-Grasp proteins have globular shape with compact structure and they are mechanically resilient. The β-clamp or mechanical clamp in them formed by the interactions between the terminal β-strands is generally associated with the protein mechanical resistance. Although previous studies showed that temperature can perturb the protein mechanical stability, the structural changes leading to the lowered mechanical resistance are not known. Here, we investigated the temperature dependent mechanical stability of small ubiquitin-related modifier 2 (SUMO2) using single-molecule force spectroscopy (SMFS) and the corresponding conformational changes using ensemble experiments. SMFS studies on the polyprotein of SUMO2 estimate a decrease in the spring constant of the protein from 4.50 to 1.35 N/m upon increasing the temperature from 5 to 45 °C. Interestingly, near-UV circular dichroism spectroscopy reveals a decrease in tertiary structure content while the overall secondary structure of the protein remains unchanged. Steady-state fluorescence and quenching studies on SUMO2 with a tryptophan mutation at the core (F60W) show that the nonpolar environment of the tryptophan is unchanged and the protein core is inaccessible to the bulk solvent, in the same temperature range. We attribute the thermal softening observed in atomic force microscopy (AFM) experiments to the reduction in tertiary structure of SUMO2. Our results provide evidence for the importance of the intramolecular interactions at the protein core along with the β-clamp or mechanical clamp in providing the mechanical resistance as well as in modulating the protein stiffness.

Identification of 2',4'-Dihydroxychalcone as an Antivirulence Agent Targeting HlyU, a Master Virulence Regulator in Vibrio vulnificus

The emergence of antimicrobial resistance and rapid acclimation allows Vibrio vulnificus to rapidly propagate in the host. This problematic pathological scenario can be circumvented by employing an antivirulence strategy, treating Vibrio infections without hindering the bacterial growth. We developed a genome-integrated orthogonal inhibitor screening platform in E. coli to identify antivirulence agents targeting a master virulence regulator of V. vulnificus. We identified 2′,4′-dihydroxychalcone (DHC) from the natural compound library and verified that it decreases the expression of the major toxin network which is equivalent to the ∆hlyU deletion mutant. 2′,4′-DHC also reduced the hemolytic activity of V. vulnificus which was tested as an example of virulence phenotype. The electrophoretic mobility shift assay confirmed that 2′,4′-DHC specifically targeted HlyU and inhibited its binding to PrtxA1 promoter. Under in vivo conditions, a single dose of 2′,4′-DHC protected ~50% wax-worm larvae from V. vulnificus infection at a non-toxic concentration to both V. vulnificus and wax-worm larvae. In the current study, we demonstrated that an orthogonal reporter system is suitable for the identification of antivirulence compounds with accuracy, and identified 2′,4′-DHC as a potent antivirulence agent that specifically targets the HlyU virulence transcriptional regulator and significantly reduces the virulence and infection potential of V. vulnificus.

A novel, easy and rapid method for constructing yeast two-hybrid vectors using In-Fusion technology

Yeast two-hybrid systems are powerful tools for analyzing interactions between proteins. Vector construction is an essential step in yeast two-hybrid experiments, which require bait and prey plasmids. In this study, we modified the multiple cloning site sequence of the yeast plasmid pGADT7 by site-directed mutagenesis PCR to generate the pGADT7-In vector, which resulted in an easy and rapid method for constructing yeast two-hybrid vectors using the In-Fusion cloning technique. This method has three key advantages: only one pair of primers and one round of PCR are needed to generate bait and prey plasmids for each gene, it is restriction endonuclease- and ligase-independent, and it is fast and easily performed.

Protein bioelectronics: a review of what we do and do not know

We review the status of protein-based molecular electronics. First, we define and discuss fundamental concepts of electron transfer and transport in and across proteins and proposed mechanisms for these processes. We then describe the immobilization of proteins to solid-state surfaces in both nanoscale and macroscopic approaches, and highlight how different methodologies can alter protein electronic properties. Because immobilizing proteins while retaining biological activity is crucial to the successful development of bioelectronic devices, we discuss this process at length. We briefly discuss computational predictions and their connection to experimental results. We then summarize how the biological activity of immobilized proteins is beneficial for bioelectronic devices, and how conductance measurements can shed light on protein properties. Finally, we consider how the research to date could influence the development of future bioelectronic devices.

Mutational Analysis of Binding Protein-Chemoreceptor Interactions

Interactions between ligands and chemoreceptors in Escherichia coli and Salmonella enterica can be studied through genetic manipulation of the actors involved. Sequence analysis and modeling can reveal potential sites of interaction, and these sites can be deleted or mutated and the effects tested through various in vivo chemotaxis assays to ascertain their importance during interaction. Here, the approach for analysis of the interaction between a major E. coli chemoreceptor and its binding protein ligand is described.

Biopharmaceuticals from microorganisms: from production to purification

The use of biopharmaceuticals dates from the 19th century and within 5–10 years, up to 50% of all drugs in development will be biopharmaceuticals. In the 1980s, the biopharmaceutical industry experienced a significant growth in the production and approval of recombinant proteins such as interferons (IFN α, β, and γ) and growth hormones. The production of biopharmaceuticals, known as bioprocess, involves a wide range of techniques. In this review, we discuss the technology involved in the bioprocess and describe the available strategies and main advances in microbial fermentation and purification process to obtain biopharmaceuticals.

Crystallizing the 6S and 8S spliceosomal assembly intermediates: a complex project

The small nuclear ribonucleoproteins (snRNPs) U1, U2, U4/6 and U5 are major constituents of the pre-mRNA processing spliceosome. They contain a common RNP core that is formed by the ordered binding of Sm proteins onto the single-stranded Sm site of the snRNA. Although spontaneous in vitro, assembly of the Sm core requires assistance from the PRMT5 and SMN complexes in vivo. To gain insight into the key steps of the assembly process, the crystal structures of two assembly intermediates of U snRNPs termed the 6S and 8S complexes have recently been reported. These multimeric protein complexes could only be crystallized after the application of various rescue strategies. The developed strategy leading to the crystallization and solution of the 8S crystal structure was subsequently used to guide a combination of rational crystal-contact optimization with surface-entropy reduction of crystals of the related 6S complex. Conversely, the resulting high-resolution 6S crystal structure was used during the restrained refinement of the 8S crystal structure.

A method for validating microRNAs in plants by miR-RACE

miRNA prediction algorithms often fail to predict the accurate location of the mature miRNA in a precursor sequence with nucleotide-level precision. miRNAs-rapid amplification of cDNA ends (miR-RACE) is an efficient method to determine the precise sequences of computationally predicted microRNAs (miRNAs). miR-RACE includes the following steps: miRNA-enriched library preparation, two specific 5'- and 3'-miRNA RACE (miR-RACE) PCR reactions, and sequence-directed cloning. The most challenging step is the two gene-specific primers designed for the two RACE reactions. The miR-RACE protocol is rapid and can be executed and completed in 2-3 days.

Mutually exclusive binding of APPL(PH) to BAR domain and Reptin regulates β-catenin dependent transcriptional events

Reptin functions in a wide range of biological processes including chromatin remodelling, nucleolar organization and transcriptional regulation of WNT signalling. As β-catenin dependent transcriptional repression and activation events involve binding of Reptin and histone deacetylase 1 to APPL endocytic proteins, this complex has become an important target to identify molecules governing endocytic processes and WNT signalling. Here, we describe the structural basis of APPL binding to Reptin to explore their mode of binding in context with APPL1/APPL2 dimerization. There is an evidence that both PH and BAR domains of APPL proteins exhibit alternately conserved regions involved in hetero-dimerization process and our in-silico data also corroborate this fact. Moreover, APPL2(PH) domain binds to the BAR domain region encompassing a nuclear localization signal. We conclude that APPL(PH) binding to BAR domain and Reptin is mutually exclusive which regulates the nucleocytoplasmic shuttling of Reptin. Furthermore, Reptin is unable to bind with membrane-associated APPL proteins. These observations were further expanded by experimental approaches where we identified a novel point mutation D316N lying in the APPL1(PH) domain which resulted in a significantly reduced binding with Reptin. By luciferase assays, we observed that overexpression of APPL1(D316N) and APPL1(WT) stimulated β-catenin/TCF dependent transcriptional activity in a similar manner which suggested that binding of Reptin to APPL1 is not necessary for β-catenin dependent target gene expression. Overall, our data attempt to highlight a comparative role of APPL proteins in controlling β-catenin dependent transcription mechanism which may improve our understanding of gene regulation.

Improving ethanol and xylitol fermentation at elevated temperature through substitution of xylose reductase in Kluyveromyces marxianus

Thermo-tolerant yeast Kluyveromyces marxianus is able to utilize a wide range of substrates, including xylose; however, the xylose fermentation ability is weak because of the redox imbalance under oxygen-limited conditions. Alleviating the intracellular redox imbalance through engineering the coenzyme specificity of NADPH-preferring xylose reductase (XR) and improving the expression of XR should promote xylose consumption and fermentation. In this study, the native xylose reductase gene (Kmxyl1) of the K. marxianus strain was substituted with XR or its mutant genes from Pichia stipitis (Scheffersomyces stipitis). The ability of the resultant recombinant strains to assimilate xylose to produce xylitol and ethanol at elevated temperature was greatly improved. The strain YZB014 expressing mutant PsXR N272D, which has a higher activity with both NADPH and NADH as the coenzyme, achieved the best results, and produced 3.55 g l(-1) ethanol and 11.32 g l(-1) xylitol-an increase of 12.24- and 2.70-fold in product at 42 °C, respectively. A 3.94-fold increase of xylose consumption was observed compared with the K. marxianus YHJ010 harboring KmXyl1. However, the strain YZB015 expressing a mutant PsXR K21A/N272D, with which co-enzyme preference was completely reversed from NADPH to NADH, failed to ferment due to the low expression. So in order to improve xylose consumption and fermentation in K. marxianus, both higher activity and co-enzyme specificity change are necessary.

Prospects for robust biocatalysis: engineering of novel specificity in a halophilic amino acid dehydrogenase

Heat- and solvent-tolerant enzymes from halophiles, potentially important industrially, offer a robust framework for protein engineering, but few solved halophilic structures exist to guide this. Homology modelling has guided mutations in glutamate dehydrogenase (GDH) from Halobacterium salinarum to emulate conversion of a mesophilic GDH to a methionine dehydrogenase. Replacement of K89, A163 and S367 by leucine, glycine and alanine converted halophilic GDH into a dehydrogenase accepting L-methionine, L-norleucine and L-norvaline as substrates. Over-expression in the halophilic expression host Haloferax volcanii and three-step purification gave ~98 % pure protein exhibiting maximum activity at pH 10. This enzyme also showed enhanced thermostability and organic solvent tolerance even at 70 °C, offering a biocatalyst resistant to harsh industrial environments. To our knowledge, this is the first reported amino acid specificity change engineered in a halophilic enzyme, encouraging use of mesophilic models to guide engineering of novel halophilic biocatalysts for industrial application. Calibrated gel filtration experiments show that both the mutant and the wild-type enzyme are stable hexamers.

Purification of plastocyanin and cytochrome c6 from plants, green algae, and cyanobacteria

Plastocyanin and cytochrome c6 are widely distributed over the oxygen-evolving photosynthetic organisms. The two proteins are functionally equivalent, but strongly differ in their global electrostatic charge. In fact, they are acidic in eukaryotes, but either neutral or basic in cyanobacteria. Such a difference in their electrostatic features is a critical factor in designing the purification procedure, which must thus be modified and adapted accordingly. This chapter reports the methods for producing (including cell cultures), isolating, and purifying plastocyanin and cytochrome c6--which greatly differ in their isoelectric point--from a number of eukaryotic and prokaryotic organisms.

Site-directed mutagenesis for improving biophysical properties of VH domains

Recombinant antibody fragments are significant therapeutic and diagnostic reagents. As such, their efficacy depends heavily on their affinities and biophysical properties. Thus, mutagenesis approaches have been extensively applied to recombinant antibodies to improve their affinity, stability, and solubility. Among the existing recombinant antibody variants, human V(H) domains stand out as the ones with the general need of solubility engineering at some point during their development; this solubility engineering step transforms V(H)s into nonaggregating, functional entities, rendering them useful as therapeutic and diagnostic reagents. Here, we present one of several approaches that have been employed to develop nonaggregating human V(H) domains. We apply an in vitro site-directed mutagenesis approach to an aggregating human V(H) domain by means of a splice overlap extension technique. The resultant mutant V(H)s are nonaggregating in contrast to the parent wild type V(H) and less prone to aggregation following thermal unfolding.

MiR-RACE, a new efficient approach to determine the precise sequences of computationally identified trifoliate orange (Poncirus trifoliata) microRNAs

BACKGROUND

Among the hundreds of genes encoding miRNAs in plants reported, much more were predicted by numerous computational methods. However, unlike protein-coding genes defined by start and stop codons, the ends of miRNA molecules do not have characteristics that can be used to define the mature miRNAs exactly, which made computational miRNA prediction methods often cannot predict the accurate location of the mature miRNA in a precursor with nucleotide-level precision. To our knowledge, there haven't been reports about comprehensive strategies determining the precise sequences, especially two termini, of these miRNAs.

METHODS

In this study, we report an efficient method to determine the precise sequences of computationally predicted microRNAs (miRNAs) that combines miRNA-enriched library preparation, two specific 5' and 3' miRNA RACE (miR-RACE) PCR reactions, and sequence-directed cloning, in which the most challenging step is the two specific gene specific primers designed for the two RACE reactions. miRNA-mediated mRNA cleavage by RLM-5' RACE and sequencing were carried out to validate the miRNAs detected. Real-time PCR was used to analyze the expression of each miRNA.

RESULTS

The efficiency of this newly developed method was validated using nine trifoliate orange (Poncirus trifoliata) miRNAs predicted computationally. The miRNAs computationally identified were validated by miR-RACE and sequencing. Quantitative analysis showed that they have variable expression. Eight target genes have been experimentally verified by detection of the miRNA-mediated mRNA cleavage in Poncirus trifoliate.

CONCLUSION

The efficient and powerful approach developed herein can be successfully used to validate the sequences of miRNAs, especially the termini, which depict the complete miRNA sequence in the computationally predicted precursor.

Sticky PCR: A PCR-based protocol for targeted protein engineering

This article describes a simple but powerful PCR-based protocol for the generation of cohesive ends on linear DNA fragments, permitting the precise engineering of DNA constructs for a variety of applications. These include the introduction of deletion mutations, domain swapping, creating hybrid DNA fusions, or targeted protein engineering. This novel method can also facilitate the cloning of large or complex DNA fragments into a relevant cloning vector independent of the use of internal restriction endonuclease sites. The protocol involves the amplification of the required fragments by polymerase chain reaction through the use of two sets of overlapping desalted oligonucleotide primers. The subsequent mixing, denaturation and re-annealing of these products present correct cohesive terminal ends for ligation. There is no requirement for special vectors, enzymes or bases, suggesting that this protocol provides a unique way of engineering constructs in a rapid and cost-effective way for specific applications, such as precise deletion or swapping of various domains of the epidermal growth factor receptor to determine their role in membrane localization.

PEPOP: computational design of immunogenic peptides

Background

Most methods available to predict protein epitopes are sequence based. There is a need for methods using 3D information for prediction of discontinuous epitopes and derived immunogenic peptides.

Results

PEPOP uses the 3D coordinates of a protein both to predict clusters of surface accessible segments that might correspond to epitopes and to design peptides to be used to raise antibodies that target the cognate antigen at specific sites. To verify the ability of PEPOP to identify epitopes, 13 crystallographically defined epitopes were compared with PEPOP clusters: specificity ranged from 0.75 to 1.00, sensitivity from 0.33 to 1.00, and the positive predictive value from 0.19 to 0.89. Comparison of these results with those obtained with two other prediction algorithms showed comparable specificity and slightly better sensitivity and PPV. To prove the capacity of PEPOP to predict immunogenic peptides that induce protein cross-reactive antibodies, several peptides were designed from the 3D structure of model antigens (IA-2, TPO, and IL8) and chemically synthesized. The reactivity of the resulting anti-peptides antibodies with the cognate antigens was measured. In 80% of the cases (four out of five peptides), the flanking protein sequence process (sequence-based) of PEPOP successfully proposed peptides that elicited antibodies cross-reacting with the parent proteins. Polyclonal antibodies raised against peptides designed from amino acids which are spatially close in the protein, but separated in the sequence, could also be obtained, although they were much less reactive. The capacity of PEPOP to design immunogenic peptides that induce antibodies suitable for a sandwich capture assay was also demonstrated.

Conclusion

PEPOP has the potential to guide experimentalists that want to localize an epitope or design immunogenic peptides for raising antibodies which target proteins at specific sites. More successful predictions of immunogenic peptides were obtained when a peptide was continuous as compared with peptides corresponding to discontinuous epitopes. PEPOP is available for use at .

Structural double-mutant cycle analysis of a hydrogen bond network in ketosteroid isomerase from Pseudomonas putida biotype B

KSI (ketosteroid isomerase) catalyses an allylic isomerization reaction at a diffusion-controlled rate. A hydrogen bond network, Asp(99).Water(504).Tyr(14).Tyr(55).Tyr(30), connects two critical catalytic residues, Tyr(14) and Asp(99), with Tyr(30), Tyr(55) and a water molecule in the highly apolar active site of the Pseudomonas putida KSI. In order to characterize the interactions among these amino acids in the hydrogen bond network of KSI, double-mutant cycle analysis was performed, and the crystal structure of each mutant protein within the cycle was determined respectively to interpret the coupling energy. The DeltaDeltaG(o) values of Y14F/D99L (Tyr(14)-->Phe/Asp(99)-->Leu) KSI, 25.5 kJ/mol for catalysis and 28.9 kJ/mol for stability, were smaller than the sums (i.e. 29.7 kJ/mol for catalysis and 34.3 kJ/mol for stability) for single mutant KSIs respectively, indicating that the effect of the Y14F/D99L mutation was partially additive for both catalysis and stability. The partially additive effect of the Y14F/D99L mutation suggests that Tyr(14) and Asp(99) should interact positively for the stabilization of the transition state during the catalysis. The crystal structure of Y14F/D99L KSI indicated that the Y14F/D99L mutation increased the hydrophobic interaction while disrupting the hydrogen bond network. The DeltaDeltaG(o) values of both Y30F/D99L and Y55F/D99L KSIs for the catalysis and stability were larger than the sum of single mutants, suggesting that either Tyr(30) and Asp(99) or Tyr(55) and Asp(99) should interact negatively for the catalysis and stability. These synergistic effects of both Y30F/D99L and Y55F/D99L mutations resulted from the disruption of the hydrogen bond network. The synergistic effect of the Y55F/D99L mutation was larger than that of the Y30F/D99L mutation, since the former mutation impaired the proper positioning of a critical catalytic residue, Tyr(14), involved in the catalysis of KSI. The present study can provide insight into interpreting the coupling energy measured by double-mutant cycle analysis based on the crystal structures of the wild-type and mutant proteins.

Approaches to DNA mutagenesis: an overview

In the last several years, the use of double-stranded DNA templates together with thermostable-polymerase PCR has essentially replaced the use single-stranded DNA templates using the thermolabile polymerase for in vitro mutagenesis. Numerous PCR methods are now available, such as overlap-extension PCR, megaprimer PCR, and inverse PCR. All these PCR methods are reliable, effective, and convenient, although they are more prone to high rates of spontaneous error in mutant DNAs than are methods using thermolabile polymerases. Some improvements, such as the introduction of methylated templates, have been employed to minimize PCR errors. On the other hand, because of the introduction of many selection measures (e.g., restoration of antibiotic resistance, restoration of replication origin and unique site elimination), both double-stranded and single-stranded DNAs can now be used as templates for mutagenesis using thermolabile polymerase methods. For PCR methods, selection measures such as nested PCR has developed. All these selection measures have greatly improved the efficiency of mutagenesis by removing wild-type templates prior to transformation. Many efficient methods are available for both SDM and REM. Mutations can be introduce in vitro or in vivo, either by mutagenic primers or by erroneous DNA synthesis. Thus, choices largely depend on the experimental needs and resources of the investigator.

Effects of codon usage and vector-host combinations on the expression of spinach plastocyanin in Escherichia coli

Spinach plastocyanin has been expressed in Escherichia coli and exported to the periplasmic space. The effects of codon usage, expression system, growth length, and temperature on expression levels in LB medium were investigated. A stretch of codons, rare in E. coli, was identified and replaced with highly expressed codons, increasing the yield by at least 20%. Plastocyanin was more efficiently expressed under the T7 promoter than under the lac promoter. Maximum yields were obtained at 37 degrees C when growing the cells for 16 h after induction. The optimized expression system produced 38 mg holoprotein per liter culture. In this system it was also possible to express plastocyanin in minimal medium, at a yield of 10 mg per liter. N-terminal sequencing and mass spectrometry showed that plastocyanin was correctly processed. The expressed plastocyanin was purified to homogeneity, as shown by an A278/A597 ratio of 1.0, and together with amino acid analysis and the determination of oxidized and total copper contents, both the absorption coefficients for epsilon 278 and for epsilon 597 were determined to be 4700 M-1 cm-1.

Characterization of plastocyanin from the cyanobacterium Phormidium laminosum: copper-inducible expression and SecA-dependent targeting in Escherichia coli

Plastocyanin from the thermophilic cyanobacterium Phormidium laminosum has been purified, a partial amino acid sequence obtained and the gene cloned and sequenced. The derived amino acid sequence indicates that the plastocyanin protein is initially synthesized with an N-terminal leader sequence of 34 amino acids to direct it across the thylakoid membrane. The leader sequence consists of a positively charged N-terminal region, a hydrophobic region and a cleavage site, which are characteristic both of higher-plant chloroplast thylakoid transfer domains and of bacterial leader peptides. The petE gene and flanking regions have been cloned in Escherichia coli, and the plastocyanin protein is expressed and directed to the periplasmic space, with concomitant processing to the mature form. Targeting to the periplasm and processing of the plastocyanin protein in E. coli appears to be dependent on components of the Sec apparatus, since the unprocessed precursor accumulates in the cytoplasm of a secA mutant. Expression of plastocyanin in E. coli is copper-inducible and apparently controlled at the level of transcription, leading to the conclusion that copper-regulated promoters exist in the regions flanking the gene and are recognized in a heterologous system. Possible implications for gene expression and protein targeting in the cyanobacterium are discussed.