Global suppression of protein folding defects and inclusion body formation

Molecular Biology Applications of Psychrophilic Enzymes: Adaptations, Advantages, Expression, and Prospective

Psychrophilic enzymes are primarily produced by microorganisms from extremely low-temperature environments which are known as psychrophiles. Their high efficiency at low temperatures and easy heat inactivation property have attracted extensive attention from various food and industrial bioprocesses. However, the application of these enzymes in molecular biology is still limited. In a previous review, the applications of psychrophilic enzymes in industries such as the detergent additives, the food additives, the bioremediation, and the pharmaceutical medicine, and cosmetics have been discussed. In this review, we discuss the main cold adaptation characteristics of psychrophiles and psychrophilic enzymes, as well as the relevant information on different psychrophilic enzymes in molecular biology. We summarize the mining and screening methods of psychrophilic enzymes. We finally recap the expression of psychrophilic enzymes. We aim to provide a reference process for the exploration and expression of new generation of psychrophilic enzymes.

Using T4 Genetics and Laemmli's Development of High Resolution SDS Gel Electrophoresis to Reveal Structural Protein Interactions Controlling Protein Folding and Phage Self-Assembly

One of the most transformative experimental techniques in the rise of modern molecular biology and biochemistry was the development of high resolution Sodium Dodecyl Sulfate (SDS) poly acrylamide gel electrophoresis, which allowed separation of proteins - including structural proteins - in complex mixtures according to their molecular weights. Its development was intimately tied to investigations of the control of virus assembly within phage-infected cells. The method was developed by Ulrich K. Laemmli working in the virus structural group led by Aaron Klug at the famed Medical Research Council Laboratory for Molecular Biology (LMB) at Cambridge, UK. While Laemmli was tackling T4 head assembly, I sat at the next bench working on T4 tail assembly. To date, Laemmli's original paper has been cited almost 300,000 times. His gel procedure and our cooperation allowed us to sort out the sequential protein-protein interactions controlling the viral self-assembly pathways. It is still not fully appreciated that this control involved protein conformational change induced by interaction with an edge of the growing structure. Subsequent efforts of my students and I to understand how temperature sensitive mutations interfered with assembly were important in revealing the intracellular off-pathway aggregation processes competing with productive protein folding. These misfolding processes slowed the initial productivity of the biotechnology industry. The article below describes the scientific origin, context and sociology that supported these advances in protein biochemistry, protein expression, and virus assembly. The cooperation and collaboration that was integral to both the LMB culture and phage genetics fields were key to these endeavors.

Polyclonal aptamer libraries as binding entities on a graphene FET based biosensor for the discrimination of apo- and holo-retinol binding protein 4

Oligonucleotide DNA aptamers represent an emergently important class of binding entities towards as different analytes as small molecules or even whole cells. Without requiring the canonical isolation of individual aptamers following the SELEX process, the focused polyclonal libraries prepared by this in vitro evolution and selection can directly be used to label their dedicated targets and to serve as binding molecules on surfaces. Here we report the first instance of a sensor able to discriminate between loaded and unloaded retinol-binding protein 4 (RBP4), an important biomarker for the prediction of diabetes and kidney disease. The sensor relies on two aptamer libraries tuned such that they discriminate between the protein isoforms, requiring no further sample labelling to detect RBP4 in both states. The evolution, binding properties of the libraries and the functionalization of graphene FET sensor chips are presented as well as the functionality of the resulting biosensor.

Identification, functional characterization and expression pattern of myeloid differentiation factor 88 (MyD88) in Nibea albiflora

Myeloid differentiation factor 88 (MyD88), composed of an N-terminal death domain and a C-terminal Toll/interleukin (IL)-IR homology domain, is a key connector protein in the TLR signal transduction pathway. In this study a novel isoform of MyD88 in Nibea albiflora (named as NaMyD88) was identified and functionally characterized (GenBank accession no. MN384261.1). Its complete cDNA sequence was 1672 bp and contained an open reading frame of 879 bp encoding 292 amino acid residues, which was similar to its teleost fish counterparts in the length. The theoretical molecular mass was 33.63 kDa and the isoelectric point was 5.24. BLASTp analysis suggested that the deduced amino acids sequence of NaMyD88 shared high identity to the known MyD88, for instance, 94.77% identity with Collichthys lucidus. Sequence analysis showed that NaMyD88 protein was consistent with MyD88 protein of other species at three conserved domains, N-terminal DD, short middle domain and C-terminal TIR, and the TIR domain contained three highly conserved motifs: Box1, Box2, and Box3. NaMyD88 and red fluorescent protein (Dsred) were fused and expressed in the cytoplasm of the epithelioma papulosum cyprini (EPC cells). The NaTLR9-TIR-EGFP fusion protein, which was obtained in our previous studies, showed green fluorescence and mainly distributed in the cytoplasm. After co-transfection, NaMyD88-Dsred and NaTLR9-TIR-EGFP obviously overlapped and displayed orange-yellow color. The results showed that the homologous MyD88-Dsred could interact with NaTLR9-TIR-EGFP. Based on this result pcMV-NaMyD88-TIR-Myc plasmids and the pcDNA3.1-NaTLR9-TIR-flag were constructed and co-transfected into 293T cells for the immunoprecipitation test. According to Western blot, the protein eluted by Flag-beads could be detected by anti-Flag-tag antibody and anti-Myc tag antibody respectively, while the protein without NaTLR9-TIR could not be found, which further proved that TLR and MyD88 could interact each other. The prokaryotic plasmid of MyD88-TIR domain was constructed, expressed in BL21 (DE3) and purified by Ni-NAT super flow resin conforming to the expected molecular weight of 27 kDa with the corresponding active sites for its conferring protein-protein interaction functions. Real-time fluorescence quantitative PCR showed that NaMyD88 could be expressed in intestine, stomach, liver, kidney, gill, heart and spleen, with the highest in the kidney, and it was up-regulated after being infected with Polyinosinic:polycytidylic acid - Poly (I:C) and Pseudomonas plecoglossicida, which showed that NaMyD88 was involved in the immune response of N.albiflora. These data afforded a basis for understanding the role of NaMyD88 in the TLR signaling pathway of N.albiflora.

CFTR trafficking mutations disrupt cotranslational protein folding by targeting biosynthetic intermediates

Protein misfolding causes a wide spectrum of human disease, and therapies that target misfolding are transforming the clinical care of cystic fibrosis. Despite this success, however, very little is known about how disease-causing mutations affect the de novo folding landscape. Here we show that inherited, disease-causing mutations located within the first nucleotide-binding domain (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) have distinct effects on nascent polypeptides. Two of these mutations (A455E and L558S) delay compaction of the nascent NBD1 during a critical window of synthesis. The observed folding defect is highly dependent on nascent chain length as well as its attachment to the ribosome. Moreover, restoration of the NBD1 cotranslational folding defect by second site suppressor mutations also partially restores folding of full-length CFTR. These findings demonstrate that nascent folding intermediates can play an important role in disease pathogenesis and thus provide potential targets for pharmacological correction.

Addition of an N-Terminal Poly-Glutamate Fusion Tag Improves Solubility and Production of Recombinant TAT-Cre Recombinase in Escherichia coli

Cre recombinase is widely used to manipulate DNA sequences for both in vitro and in vivo research. Attachment of a trans-activator of transcription (TAT) sequence to Cre allows TATCre to penetrate the cell membrane, and the addition of a nuclear localization signal (NLS) helps the enzyme to translocate into the nucleus. Since the yield of recombinant TAT-Cre is limited by formation of inclusion bodies, we hypothesized that the positively charged arginine-rich TAT sequence causes the inclusion body formation, whereas its neutralization by the addition of a negatively charged sequence improves solubility of the protein. To prove this, we neutralized the positively charged TAT sequence by proximally attaching a negatively charged poly-glutamate (E12) sequence. We found that the E12 tag improved the solubility and yield of E12-TAT-NLS-Cre (E12-TAT-Cre) compared with those of TAT-NLS-Cre (TATCre) when expressed in E. coli. Furthermore, the growth of cells expressing E12-TAT-Cre was increased compared with that of the cells expressing TAT-Cre. Efficacy of the purified TATCre was confirmed by a recombination test on a floxed plasmid in a cell-free system and 293 FT cells. Taken together, our results suggest that attachment of the E12 sequence to TAT-Cre improves its solubility during expression in E. coli (possibly by neutralizing the ionic-charge effects of the TAT sequence) and consequently increases the yield. This method can be applied to the production of transducible proteins for research and therapeutic purposes.

Enhanced production of recombinant serratiopeptidase in Escherichia coli and its characterization as a potential biosimilar to native biotherapeutic counterpart

BACKGROUND

Serratia marcescens, a Gram-negative nosocomial pathogen secretes a 50 kDa multi-domain zinc metalloprotease called serratiopeptidase. Broad substrate specificity of serratiopeptidase makes it suitable for detergent and food processing industries The protein shows potent anti-inflammatory, anti-edemic, analgesic, antibiofilm activity and sold as an individual or fixed-dose enteric-coated tablets combined with other drugs. Although controversial, serratiopeptidase as drug is used in the treatment of chronic sinusitis, carpal tunnel syndrome, sprains, torn ligaments, and postoperative inflammation. Since the native producer of serratiopeptidase is a pathogenic microorganism, the current production methods need to be replaced by alternative approaches. Heterologous expression of serratiopeptidase in E. coli was tried before but not found suitable due to the limited yield, and other expression related issues due to its inherent proteolytic activity such as cytotoxicity, cell death, no expression, minimal expression, or inactive protein accumulation.

RESULTS

Recombinant expression of mature form serratiopeptidase in E. coli seems toxic and resulted in the failure of transformation and other expression related issues. Although E. coli C43(DE3) cells, express protein correctly, the yield was compromised severely. Optimization of protein expression process parameters such as nutrient composition, induction point, inducer concentration, post-induction duration, etc., caused significant enhancement in serratiopeptidase production (57.9 ± 0.73% of total cellular protein). Expressed protein formed insoluble, enzymatically inactive inclusion bodies, and gave 40-45 mg/l homogenous (> 98% purity) biologically active and conformationally similar serratiopeptidase to the commercial counterpart upon refolding and purification.

CONCLUSION

Expression of mature serratiopeptidase in E. coli C43(DE3) cells eliminated the protein expression associated with toxicity issues. Further optimization of process parameters significantly enhanced the overexpression of protein resulting in the higher yield of pure and functionally active recombinant serratiopeptidase. The biological activity and conformational features of recombinant serratiopeptidase were very similar to the commercially available counterpart suggesting it-a potential biosimilar of therapeutic and industrial relevance.

Bacterial inclusion bodies are industrially exploitable amyloids

Understanding the structure, functionalities and biology of functional amyloids is an issue of emerging interest. Inclusion bodies, namely protein clusters formed in recombinant bacteria during protein production processes, have emerged as unanticipated, highly tunable models for the scrutiny of the physiology and architecture of functional amyloids. Based on an amyloidal skeleton combined with varying amounts of native or native-like protein forms, bacterial inclusion bodies exhibit an unusual arrangement that confers mechanical stability, biological activity and conditional protein release, being thus exploitable as versatile biomaterials. The applicability of inclusion bodies in biotechnology as enriched sources of protein and reusable catalysts, and in biomedicine as biocompatible topographies, nanopills or mimetics of endocrine secretory granules has been largely validated. Beyond these uses, the dissection of how recombinant bacteria manage the aggregation of functional protein species into structures of highly variable complexity offers insights about unsuspected connections between protein quality (conformational status compatible with functionality) and cell physiology.

[Investigation the role of mutations M182T and Q39K in structure of beta-lactamase TEM-72 by molecular dynamics method]

Synthesis of b-lactamases is one of the common mechanisms of bacterial resistance to b-lactam antibiotics including penicillins and cephalosporins. The widespread use of antibiotics results in appearance of numerous extended-spectrum b-lactamase variants or resistance to inhibitors. Mutations of 92 residues of TEM type were found. Several mutations are the key mutations that determine the extension of spectrum of substrates. However, roles of the most associated mutations, located far from active site, remain unknown. We have investigated the role of associated mutations in structure of b-lactamase TEM-72, which contain two key mutation (G238S, E240K) and two associated mutations (Q39K, M182T) by means of simulation of molecular dynamics. The key mutation lead to destabilization of the protein globule, characterized by increased mobility of amino acid residues at high temperature of modelling. Mutation M182T lead to stabilization protein, whereas mutation Q39K is destabilizing mutation. It seems that the last mutation serves for optimization of conformational mobility of b-lactamase and may influence on enzyme activity.

Production and characterization of a novel antifungal chitinase identified by functional screening of a suppressive-soil metagenome

Background

Through functional screening of a fosmid library, generated from a phytopathogen-suppressive soil metagenome, the novel antifungal chitinase—named Chi18H8 and belonging to family 18 glycosyl hydrolases—was previously discovered. The initial extremely low yield of Chi18H8 recombinant production and purification from Escherichia coli cells (21 μg/g cell) limited its characterization, thus preventing further investigation on its biotechnological potential.

Results

We report on how we succeeded in producing hundreds of milligrams of pure and biologically active Chi18H8 by developing and scaling up to a high-yielding, 30 L bioreactor process, based on a novel method of mild solubilization of E. coli inclusion bodies in lactic acid aqueous solution, coupled with a single step purification by hydrophobic interaction chromatography. Chi18H8 was characterized as a Ca²⁺-dependent mesophilic chitobiosidase, active on chitin substrates at acidic pHs and possessing interesting features, such as solvent tolerance, long-term stability in acidic environment and antifungal activity against the phytopathogens Fusarium graminearum and Rhizoctonia solani. Additionally, Chi18H8 was found to operate according to a non-processive endomode of action on a water-soluble chitin-like substrate.

Conclusions

Expression screening of a metagenomic library may allow access to the functional diversity of uncultivable microbiota and to the discovery of novel enzymes useful for biotechnological applications. A persisting bottleneck, however, is the lack of methods for large scale production of metagenome-sourced enzymes from genes of unknown origin in the commonly used microbial hosts. To our knowledge, this is the first report on a novel metagenome-sourced enzyme produced in hundreds-of-milligram amount by recovering the protein in the biologically active form from recombinant E. coli inclusion bodies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0634-8) contains supplementary material, which is available to authorized users.

Widespread Historical Contingency in Influenza Viruses

In systems biology and genomics, epistasis characterizes the impact that a substitution at a particular location in a genome can have on a substitution at another location. This phenomenon is often implicated in the evolution of drug resistance or to explain why particular "disease-causing" mutations do not have the same outcome in all individuals. Hence, uncovering these mutations and their locations in a genome is a central question in biology. However, epistasis is notoriously difficult to uncover, especially in fast-evolving organisms. Here, we present a novel statistical approach that replies on a model developed in ecology and that we adapt to analyze genetic data in fast-evolving systems such as the influenza A virus. We validate the approach using a two-pronged strategy: extensive simulations demonstrate a low-to-moderate sensitivity with excellent specificity and precision, while analyses of experimentally validated data recover known interactions, including in a eukaryotic system. We further evaluate the ability of our approach to detect correlated evolution during antigenic shifts or at the emergence of drug resistance. We show that in all cases, correlated evolution is prevalent in influenza A viruses, involving many pairs of sites linked together in chains; a hallmark of historical contingency. Strikingly, interacting sites are separated by large physical distances, which entails either long-range conformational changes or functional tradeoffs, for which we find support with the emergence of drug resistance. Our work paves a new way for the unbiased detection of epistasis in a wide range of organisms by performing whole-genome scans.

Protein recovery from inclusion bodies of Escherichia coli using mild solubilization process

Formation of inclusion bodies in bacterial hosts poses a major challenge for large scale recovery of bioactive proteins. The process of obtaining bioactive protein from inclusion bodies is labor intensive and the yields of recombinant protein are often low. Here we review the developments in the field that are targeted at improving the yield, as well as quality of the recombinant protein by optimizing the individual steps of the process, especially solubilization of the inclusion bodies and refolding of the solubilized protein. Mild solubilization methods have been discussed which are based on the understanding of the fact that protein molecules in inclusion body aggregates have native-like structure. These methods solubilize the inclusion body aggregates while preserving the native-like protein structure. Subsequent protein refolding and purification results in high recovery of bioactive protein. Other parameters which influence the overall recovery of bioactive protein from inclusion bodies have also been discussed. A schematic model describing the utility of mild solubilization methods for high throughput recovery of bioactive protein has also been presented.

Wild-type human γD-crystallin promotes aggregation of its oxidation-mimicking, misfolding-prone W42Q mutant

Non-native protein conformers generated by mutation or chemical damage template aggregation of wild-type, undamaged polypeptides in diseases ranging from amyotrophic lateral sclerosis to cancer. We tested for such interactions in the natively monomeric human eye lens protein γd-crystallin, whose aggregation leads to cataract disease. The oxidation-mimicking W42Q mutant of γd-crystallin formed non-native polymers starting from a native-like state under physiological conditions. Aggregation occurred in the temperature range 35-45 °C, in which the mutant protein began to lose the native conformation of its N-terminal domain. Surprisingly, wild-type γd-crystallin promoted W42Q polymerization in a catalytic manner, even at mutant concentrations too low for homogeneous nucleation to occur. The presence of wild-type protein also downshifted the temperature range of W42Q aggregation. W42Q aggregation required formation of a non-native intramolecular disulfide bond but not intermolecular cross-linking. Transient WT/W42Q binding may catalyze this oxidative misfolding event in the mutant. That a more stable variant in a mixture can specifically promote aggregation of a less stable one rationalizes how extensive aggregation of rare damaged polypeptides can occur during the course of aging.

Mutational studies on resurrected ancestral proteins reveal conservation of site-specific amino acid preferences throughout evolutionary history

Local protein interactions (“molecular context” effects) dictate amino acid replacements and can be described in terms of site-specific, energetic preferences for any different amino acid. It has been recently debated whether these preferences remain approximately constant during evolution or whether, due to coevolution of sites, they change strongly. Such research highlights an unresolved and fundamental issue with far-reaching implications for phylogenetic analysis and molecular evolution modeling. Here, we take advantage of the recent availability of phenotypically supported laboratory resurrections of Precambrian thioredoxins and β-lactamases to experimentally address the change of site-specific amino acid preferences over long geological timescales. Extensive mutational analyses support the notion that evolutionary adjustment to a new amino acid may occur, but to a large extent this is insufficient to erase the primitive preference for amino acid replacements. Generally, site-specific amino acid preferences appear to remain conserved throughout evolutionary history despite local sequence divergence. We show such preference conservation to be readily understandable in molecular terms and we provide crystallographic evidence for an intriguing structural-switch mechanism: Energetic preference for an ancestral amino acid in a modern protein can be linked to reorganization upon mutation to the ancestral local structure around the mutated site. Finally, we point out that site-specific preference conservation naturally leads to one plausible evolutionary explanation for the existence of intragenic global suppressor mutations.

Folding the proteome

Protein folding is an essential prerequisite for protein function and hence cell function. Kinetic and thermodynamic studies of small proteins that refold reversibly were essential for developing our current understanding of the fundamentals of protein folding mechanisms. However, we still lack sufficient understanding to accurately predict protein structures from sequences, or the effects of disease-causing mutations. To date, model proteins selected for folding studies represent only a small fraction of the complexity of the proteome and are unlikely to exhibit the breadth of folding mechanisms used in vivo. We are in urgent need of new methods - both theoretical and experimental - that can quantify the folding behavior of a truly broad set of proteins under in vivo conditions. Such a shift in focus will provide a more comprehensive framework from which to understand the connections between protein folding, the molecular basis of disease, and cell function and evolution.

Characterization of a KCS-like KASII from Jessenia bataua that elongates saturated and monounsaturated stearic acids in Arabidopsis thaliana

As the world population grows, the demand for food increases. Although vegetable oils provide an affordable and rich source of energy, the supply of vegetable oils available for human consumption is limited by the "fuel vs food" debate. To increase the nutritional value of vegetable oil, metabolic engineering may be used to produce oil crops of desirable fatty acid composition. We have isolated and characterized β-ketoacyl ACP-synthase II (KASII) cDNA from a high-oleic acid palm, Jessenia bataua. Jessenia KASII (JbKASII) encodes a 488-amino acid polypeptide that possesses conserved domains that are necessary for condensing activities. When overexpressed in E. coli, recombinant His-tagged JbKASII was insoluble and non-functional. However, Arabidopsis plants expressing GFP-JbKASII fusions had elevated levels of arachidic acid (C20:0) and erucic acid (C22:1) at the expense of stearic acid (C18:0) and oleic acid (C18:1). Furthermore, JbKASII failed to complement the Arabidopsis KASII mutant, fab1-2. This suggests that the substrate specificity of JbKASII is similar to that of ketoacyl-CoA synthase (KCS), which preferentially elongates stearic and oleic acids, and not palmitic acid. Our results suggest that the KCS-like JbKASII may elongate C18:0 and C18:1 to yield C20:0 and C22:1, respectively. JbKASII may, therefore, be an interesting candidate gene for promoting the production of very long chain fatty acids in transgenic oil crops.

A computational-experimental approach identifies mutations that enhance surface expression of an oseltamivir-resistant influenza neuraminidase

The His274→Tyr (H274Y) oseltamivir (Tamiflu) resistance mutation causes a substantial decrease in the total levels of surface-expressed neuraminidase protein and activity in early isolates of human seasonal H1N1 influenza, and in the swine-origin pandemic H1N1. In seasonal H1N1, H274Y only became widespread after the occurrence of secondary mutations that counteracted this decrease. H274Y is currently rare in pandemic H1N1, and it remains unclear whether secondary mutations exist that might similarly counteract the decreased neuraminidase surface expression associated with this resistance mutation in pandemic H1N1. Here we investigate the possibility of predicting such secondary mutations. We first test the ability of several computational approaches to retrospectively identify the secondary mutations that enhanced levels of surface-expressed neuraminidase protein and activity in seasonal H1N1 shortly before the emergence of oseltamivir resistance. We then use the most successful computational approach to predict a set of candidate secondary mutations to the pandemic H1N1 neuraminidase. We experimentally screen these mutations, and find that several of them do indeed partially counteract the decrease in neuraminidase surface expression caused by H274Y. Two of the secondary mutations together restore surface-expressed neuraminidase activity to wildtype levels, and also eliminate the very slight decrease in viral growth in tissue-culture caused by H274Y. Our work therefore demonstrates a combined computational-experimental approach for identifying mutations that enhance neuraminidase surface expression, and describes several specific mutations with the potential to be of relevance to the spread of oseltamivir resistance in pandemic H1N1.

Mechanisms for the evolution of a derived function in the ancestral glucocorticoid receptor

Understanding the genetic, structural, and biophysical mechanisms that caused protein functions to evolve is a central goal of molecular evolutionary studies. Ancestral sequence reconstruction (ASR) offers an experimental approach to these questions. Here we use ASR to shed light on the earliest functions and evolution of the glucocorticoid receptor (GR), a steroid-activated transcription factor that plays a key role in the regulation of vertebrate physiology. Prior work showed that GR and its paralog, the mineralocorticoid receptor (MR), duplicated from a common ancestor roughly 450 million years ago; the ancestral functions were largely conserved in the MR lineage, but the functions of GRs-reduced sensitivity to all hormones and increased selectivity for glucocorticoids-are derived. Although the mechanisms for the evolution of glucocorticoid specificity have been identified, how reduced sensitivity evolved has not yet been studied. Here we report on the reconstruction of the deepest ancestor in the GR lineage (AncGR1) and demonstrate that GR's reduced sensitivity evolved before the acquisition of restricted hormone specificity, shortly after the GR-MR split. Using site-directed mutagenesis, X-ray crystallography, and computational analyses of protein stability to recapitulate and determine the effects of historical mutations, we show that AncGR1's reduced ligand sensitivity evolved primarily due to three key substitutions. Two large-effect mutations weakened hydrogen bonds and van der Waals interactions within the ancestral protein, reducing its stability. The degenerative effect of these two mutations is extremely strong, but a third permissive substitution, which has no apparent effect on function in the ancestral background and is likely to have occurred first, buffered the effects of the destabilizing mutations. Taken together, our results highlight the potentially creative role of substitutions that partially degrade protein structure and function and reinforce the importance of permissive mutations in protein evolution.

Multiple global suppressors of protein stability defects facilitate the evolution of extended-spectrum TEM β-lactamases

The introduction of extended-spectrum cephalosporins and β-lactamase inhibitors has driven the evolution of extended-spectrum β-lactamases (ESBLs) that possess the ability to hydrolyze these drugs. The evolved TEM ESBLs from clinical isolates of bacteria often contain substitutions that occur in the active site and alter the catalytic properties of the enzyme to provide an increased hydrolysis of extended-spectrum cephalosporins or an increased resistance to inhibitors. These active-site substitutions often result in a cost in the form of reduced enzyme stability. The evolution of TEM ESBLs is facilitated by mutations that act as global suppressors of protein stability defects in that they allow the enzyme to absorb multiple amino acid changes despite incremental losses in stability associated with the substitutions. The best-studied example is the M182T substitution, which corrects protein stability defects and is commonly found in TEM ESBLs or inhibitor-resistant variants from clinical isolates. In this study, a genetic selection for second-site mutations that could partially restore function to a severely destabilized primary mutant enabled the identification of A184V, T265M, R275Q, and N276D, which are known to occur in TEM ESBLs from clinical isolates, as suppressors of TEM-1 protein stability defects. Further characterization demonstrated that these substitutions increased the thermal stability of TEM-1 and were able to correct the stability defects of two different sets of destabilizing mutations. The acquisition of compensatory global suppressors of stability costs associated with active-site mutations may be a common mechanism for the evolution of novel protein function.

Permissive secondary mutations enable the evolution of influenza oseltamivir resistance

The His274-->Tyr274 (H274Y) mutation confers oseltamivir resistance on N1 influenza neuraminidase but had long been thought to compromise viral fitness. However, beginning in 2007-2008, viruses containing H274Y rapidly became predominant among human seasonal H1N1 isolates. We show that H274Y decreases the amount of neuraminidase that reaches the cell surface and that this defect can be counteracted by secondary mutations that also restore viral fitness. Two such mutations occurred in seasonal H1N1 shortly before the widespread appearance of H274Y. The evolution of oseltamivir resistance was therefore enabled by "permissive" mutations that allowed the virus to tolerate subsequent occurrences of H274Y. An understanding of this process may provide a basis for predicting the evolution of oseltamivir resistance in other influenza strains.

Fundamental link between folding states and functional states of proteins

Folding and function of proteins are two aspects of proteins which are usually considered as basically unrelated phenomena that are optimized by evolution independently. From the funnel model of folding/unfolding and the associated energy landscape, we infer the paradigm that the minimum number of folding intermediates is determined by the number of all functional states of a protein ("essential" folding intermediates). Here, we demonstrate the supposed fundamental link using the Ras protein complexed with the GTP analogue GppNHp that occurs in two structural states coexisting in solution. State 2 was shown earlier to represent the effector interacting state, and the function of state 1 was hitherto unknown. By (31)P NMR spectroscopy, we demonstrate that state 1 represents the conformation interacting with guanine nucleotide exchange factors (GEFs). Denaturation experiments of the protein with a chaotropic reagent show that both functional states coexist during folding and unfolding. Application of high pressure represents another perturbation of the energy landscape, leading to an increased population of the state 1 as observed by NMR spectroscopy. The specific volume difference between the two states DeltaV(12) is 17.2 +/- 0.5 mL mol(-1), indicating that state 1 represents a more open conformation of the protein. The free energies of stabilization for state 1 and state 2 at 278 K can be determined as 8.3 and 9.8 kJ mol(-1), respectively.

Protein aggregation from inclusion bodies to amyloid and biomaterials

Inclusion bodies and amyloid are two different outcomes of the same fundamental biological process: protein aggregation. They share two important features that suggest sequence-specific aggregation: oligomeric intermediates as precursors to the aggregated sate and sensitivity to site-specific point mutations. For a long time, the physical state of inclusion bodies was refractory to the use of protein structural characterization techniques that were developed for soluble proteins. Recent high-resolution studies reveal that the apparently amorphous state of these dense protein agglomerates consists of amyloid-type structures adopted by short segments that initiate aggregation. Under certain circumstances it is possible for the aggregation-prone segments to "recruit" a globular counterpart within the inclusion body, with the latter being able to fold into an active conformation. In this chapter we will discuss these recent structural insights in relation with the also recent, high-resolution structures for amyloid "spines" and their ability to accommodate globular or "swapped" domains in their periphery. Finally, unexpected natural roles for amyloid structures such as protection, adhesion, and storage materials gradually emerge. We will discuss how these properties in combination with biochemical and structural insights can inspire "biomimetic" approaches for the rational design of novel nanobiomaterials.

The mechanism of folding of Im7 reveals competition between functional and kinetic evolutionary constraints

Many proteins reach their native state through pathways involving the presence of folding intermediates. It is not clear whether this type of folding landscape results from insufficient evolutionary pressure to optimize folding efficiency, or arises from a conflict between functional and folding constraints. Here, using protein-engineering, ultra-rapid mixing and stopped-flow experiments combined with restrained molecular dynamics simulations, we characterize the transition state for the formation of the intermediate populated during the folding of the bacterial immunity protein, Im7, and the subsequent molecular steps leading to the native state. The results provide a comprehensive view of the folding process of this small protein. An analysis of the contributions of native and non-native interactions at different stages of folding reveals how the complexity of the folding landscape arises from concomitant evolutionary pressures for function and folding efficiency.

Purification of truncated and mutated Chemotaxis Inhibitory Protein of Staphylococcus aureus--an anti-inflammatory protein

The Chemotaxis Inhibitory Protein of Staphylococcus aureus (CHIPS) binds and blocks the C5a receptor (C5aR) and formyl-peptide receptor (FPR). This way, CHIPS is a potent inhibitor of the immune cell recruitment associated with inflammation. Truncation of the protein and the introduction of mutations, shifts the expression towards the insoluble fraction of Escherichia coli, whereas the wild-type protein can be solubly expressed. A protocol for expression and tag independent purification of biologically active CHIPS variants has been established to enable further characterization of an improved CHIPS variant, called ADC-1004. The CHIPS variants were purified by washing of E. coli inclusion bodies followed by refolding and gel filtration. New techniques were utilized to optimize the purification process. Expression in inclusion bodies was increased by the use of Ultra Yield flasks and optimal refolding conditions were determined by the use of the iFOLD Refolding System 2. The folding and biological activity of the purified proteins were analyzed by circular dichroism (CD) spectroscopy and flow cytometry, respectively, and compared to solubly produced CHIPS(31-113) and wild-type CHIPS(1-121). We show that the CHIPS variants produced in inclusion bodies can be refolded and purified to achieve equal biological activity as solubly produced CHIPS(31-113) and wild-type CHIPS(1-121). The truncation causes minor structural changes while purification from inclusion bodies or the soluble fraction does not further affect the structure.

Cotranslational folding promotes beta-helix formation and avoids aggregation in vivo

Newly synthesized proteins must form their native structures in the crowded environment of the cell, while avoiding non-native conformations that can lead to aggregation. Yet, remarkably little is known about the progressive folding of polypeptide chains during chain synthesis by the ribosome or of the influence of this folding environment on productive folding in vivo. P22 tailspike is a homotrimeric protein that is prone to aggregation via misfolding of its central beta-helix domain in vitro. We have produced stalled ribosome:tailspike nascent chain complexes of four fixed lengths in vivo, in order to assess cotranslational folding of newly synthesized tailspike chains as a function of chain length. Partially synthesized, ribosome-bound nascent tailspike chains populate stable conformations with some native-state structural features even prior to the appearance of the entire beta-helix domain, regardless of the presence of the chaperone trigger factor, yet these conformations are distinct from the conformations of released, refolded tailspike truncations. These results suggest that organization of the aggregation-prone beta-helix domain occurs cotranslationally, prior to chain release, to a conformation that is distinct from the accessible energy minimum conformation for the truncated free chain in solution.

Choice of cellular protein expression system

Recombinant protein expression has become a standard laboratory tool, and a wide variety of systems and techniques are now in use. Because there are so many systems to choose from, the investigator has to be careful to use the combination that will give the best results for the protein being studied. This overview unit discusses expression and production choices, including post-translational modifications (e.g., glycosylation, acylation, sulfation, and removal of N-terminal methionine), in vivo and in vitro folding, and influence of downstream elements on expression.

Polyhead formation in phage P22 pinpoints a region in coat protein required for conformational switching

Eighteen single amino acid substitutions in phage P22 coat protein cause temperature-sensitive folding defects (tsf). Three intragenic global suppressor (su) substitutions (D163G, T166I and F170L), localized to a flexible loop, rescue the folding of several tsf coat proteins. Here we investigate the su substitutions in the absence of the original tsf substitutions. None of the su variant coat proteins displayed protein folding defects. Individual su substitutions had little effect on phage production in vivo; yet double and triple combinations resulted in a cold-sensitive (cs) phenotype, consistent with a defect in assembly. During virus assembly and maturation, conformational switching of capsid subunits is required when chemically identical capsid subunits form an icosahedron. Analysis of double- and triple-su phage-infected cell lysates by negative-stain electron microscopy reveals an increase in aberrant structures at the cs temperature. In vitro assembly of F170L coat protein causes production of polyheads, never seen before in phage P22. Purified procapsids composed of all of the su coat proteins showed defects in expansion, which mimics maturation in vitro. Our results suggest that a previously identified surface-exposed loop in coat protein is critical in conformational switching of subunits during both procapsid assembly and maturation.

Chemical chaperone-mediated protein folding: stabilization of P22 tailspike folding intermediates by glycerol

Polyol co-solvents such as glycerol increase the thermal stability of proteins. This has been explained by preferential hydration favoring the more compact native over the denatured state. Although polyols are also expected to favor aggregation by the same mechanism, they have been found to increase the folding yields of some large, aggregation-prone proteins. We have used the homotrimeric phage P22 tailspike protein to investigate the origin of this effect. The folding of this protein is temperature-sensitive and limited by the stability of monomeric folding intermediates. At non-permissive temperature (≥35°C), tailspike refolding yields were increased significantly in the presence of 1–4 mglycerol. At low temperature, tailspike refolding is prevented when folding intermediates are destabilized by the addition of urea. Glycerol could offset the urea effect, suggesting that the polyol acts by stabilizing crucial folding intermediates and not by increasing solvent viscosity. The stabilization effect of glycerol on tailspike folding intermediates was confirmed in experiments using a temperature-sensitive folding mutant protein, by fluorescence measurements of subunit folding kinetics, and by temperature up-shift experiments. Our results suggest that the chemical chaperone effect of polyols observed in the folding of large proteins is due to preferential hydration favoring structure formation in folding intermediates.

Aeropin from the extremophile Pyrobaculum aerophilum bypasses the serpin misfolding trap

Serpins are metastable proteinase inhibitors. Serpin metastability drives both a large conformational change that is utilized during proteinase inhibition and confers an inherent structural flexibility that renders serpins susceptible to aggregation under certain conditions. These include point mutations (the basis of a number of important human genetic diseases), small changes in pH, and an increase in temperature. Many studies of serpins from mesophilic organisms have highlighted an inverse relationship: mutations that confer a marked increase in serpin stability compromise inhibitory activity. Here we present the first biophysical characterization of a metastable serpin from a hyperthermophilic organism. Aeropin, from the archaeon Pyrobaculum aerophilum, is both highly stable and an efficient proteinase inhibitor. We also demonstrate that because of high kinetic barriers, aeropin does not readily form the partially unfolded precursor to serpin aggregation. We conclude that stability and activity are not mutually exclusive properties in the context of the serpin fold, and propose that the increased stability of aeropin is caused by an unfolding pathway that minimizes the formation of an aggregation-prone intermediate ensemble, thereby enabling aeropin to bypass the misfolding fate observed with other serpins.

GroEL/S substrate specificity based on substrate unfolding propensity

Phage P22 wild-type (WT) coat protein does not require GroEL/S to fold but temperature-sensitive-folding (tsf) coat proteins need the chaperone complex for correct folding. WT coat protein and all variants absolutely require P22 scaffolding protein, an assembly chaperone, to assemble into precursor structures termed procapsids. Previously, we showed that a global suppressor (su) substitution, T1661, which rescues several tsf coat protein variants, functioned by inducing GroEL/S. This led to an increased formation of tsf:T1661 coat protein:GroEL complexes compared with the tsf parents. The increased concentration of complexes resulted in more assembly-competent coat proteins because of a shift in the chaperone-driven kinetic partitioning between aggregation-prone intermediates toward correct folding and assembly. We have now investigated the folding and assembly of coat protein variants that carry a different global su substitution, F170L. By monitoring levels of phage production in the presence of a dysfunctional GroEL we found that tsf:F170L proteins demonstrate a less stringent requirement for GroEL. Tsf:F170L proteins also did not cause induction of the chaperones. Circular dichroism and tryptophan fluorescence indicate that the native state of the tsf: F170L coat proteins is restored to WT-like values. In addition, native acrylamide gel electrophoresis shows a stabilized native state for tsf:F170L coat proteins. The F170L su substitution also increases procapsid production compared with their tsf parents. We propose that the F170L su substitution has a decreased requirement for the chaperones GroEL and GroES as a result of restoring the tsf coat proteins to a WT-like state. Our data also suggest that GroEL/S can be induced by increasing the population of unfolding intermediates.

Comparative Evaluation of α-Amylase Refolding Through Two Different Artificial Chaperone Systems

Two different artificial chaperone systems were evaluated in this work using either detergents or CDs as the stripping agents. Upon dilution of urea-denatured alpha-amylase to a non-denaturing urea concentration in the presence of the capturing agent, complexes of the detergent and non-native protein molecules are formed and thereby the formation of protein aggregates is prevented. The so-called captured protein is unable to refold from the detergent-protein complex states unless a stripping agent is used to remove the detergent molecules. Our results by fluorescence, UV, turbidity measurement, circular dichroism, surface tension and activity assay indicated that the extent of refolding assistance was different due to different inter- and intra- molecular interactions in the two different systems. However, the high activity recovery in the presence of detergents, as the stripping agent, suggests that they can constitute suitable replacement for the more expensive and common stripping agent of cyclodextrins.

Kinetics and thermodynamics of amyloid fibril assembly

With some exceptions, amyloids appear to be accidental aggregated structures whose formation was not selected for in molecular evolution. Despite this, amyloid fibrils are in many respects surprisingly well-behaved molecules. For example, Huntington's disease-related polyglutamine sequences aggregate via a relatively simple nucleated growth polymerization mechanism. In addition, the Alzheimer's plaque protein Abeta has been shown to undergo reversible amyloid fibril formation to a position of dynamic equilibrium such that reaction thermodynamics can be quantified. Studies of these well-behaved amyloid systems are allowing us to peer more deeply into the process and products of off-pathway misfolding and aggregation.

Modulation of protein aggregation by polyethylene glycol conjugation: GCSF as a case study

Polyethylene glycol (PEG) conjugation to proteins has emerged as an important technology to produce drug molecules with sustained duration in the body. However, the implications of PEG conjugation to protein aggregation have not been well understood. In this study, conducted under physiological pH and temperature, N-terminal attachment of a 20 kDa PEG moiety to GCSF had the ability to (1) prevent protein precipitation by rendering the aggregates soluble, and (2) slow the rate of aggregation relative to GCSF. Our data suggest that PEG-GCSF solubility was mediated by favorable solvation of water molecules around the PEG group. PEG-GCSF appeared to aggregate on the same pathway as that of GCSF, as evidenced by (a) almost identical secondary structural transitions accompanying aggregation, (b) almost identical covalent character in the aggregates, and (c) the ability of PEG-GCSF to rescue GCSF precipitation. To understand the role of PEG length, the aggregation properties of free GCSF were compared to 5kPEG-GCSF and 20kPEG-GCSF. It was observed that even 5kPEG-GCSF avoided precipitation by forming soluble aggregates, and the stability toward aggregation was vastly improved compared to GCSF, but only marginally less stable than the 20kPEG-GCSF. Biological activity measurements demonstrated that both 5kPEG-GCSF and 20kPEG-GCSF retained greater activity after incubation at physiological conditions than free GCSF, consistent with the stability measurements. The data is most compatible with a model where PEG conjugation preserves the mechanism underlying protein aggregation in GCSF, steric hindrance by PEG influences aggregation rate, while aqueous solubility is mediated by polar PEG groups on the aggregate surface.

Frequencies of hydrophobic and hydrophilic runs and alternations in proteins of known structure

Patterns of alternation of hydrophobic and polar residues are a profound aspect of amino acid sequences, but a feature not easily interpreted for soluble proteins. Here we report statistics of hydrophobicity patterns in proteins of known structure in a current protein database as compared with results from earlier, more limited structure sets. Previous studies indicated that long hydrophobic runs, common in membrane proteins, are underrepresented in soluble proteins. Long runs of hydrophobic residues remain significantly underrepresented in soluble proteins, with none longer than 16 residues observed. These long runs most commonly occur as buried alpha helices, with extended hydrophobic strands less common. Avoiding aggregation of partially folded intermediates during intracellular folding remains a viable explanation for the rarity of long hydrophobic runs in soluble proteins. Comparison between database editions reveals robustness of statistics on aqueous proteins despite an approximately twofold increase in nonredundant sequences. The expanded database does now allow us to explain several deviations of hydrophobicity statistics from models of random sequence in terms of requirements of specific secondary structure elements. Comparison to prior membrane-bound protein sequences, however, shows significant qualitative changes, with the average hydrophobicity and frequency of long runs of hydrophobic residues noticeably increasing between the database editions. These results suggest that the aqueous proteins of solved structure may represent an essentially complete sample of the universe of aqueous sequences, while the membrane proteins of known structure are not yet representative of the universe of membrane-associated proteins, even by relatively simple measures of hydrophobic patterns.

Artificial chaperone-assisted refolding of GuHCl-denatured alpha-amylase at low temperature: refolding versus aggregation

Refolding of GuHCl-denatured alpha-amylase was investigated using the artificial chaperone-assisted method. Three different cationic detergents (CTAB, TTAB and DTAB) and two nonionic detergents (Tween 80 and Triton X-100) were evaluated as the capturing reagents along with alpha- and beta-CD as the stripping agents. The refolding yields, at a final protein concentration of 0.15 mg/ml, were 82, 71 and 66% in the presence of beta-CD and CTAB, TTAB or DTAB, respectively. To improve the refolding yield and to suppress the extent of aggregation, the initial rate of the stripping step was slowed down by maintaining the refolding environment at 4 degrees C for about 3 min followed by raising the temperature to 25 degrees C. Under this thermal procedure, the refolding yield and the extent of aggregation were changed from 82 and 25% at 25 degrees C to 94 and 7% at 4 degrees C, respectively. These findings may assist the activity recovery of recombinant proteins at relatively high concentrations.

An elongated spine of buried core residues necessary for in vivo folding of the parallel beta-helix of P22 tailspike adhesin

The parallel beta-helix is an elongated beta-sheet protein domain associated with microbial virulence factors, toxins, viral adhesins, and allergens. Long stacks of similar, buried residues are a prominent feature of this fold, as well as the polypeptide chain fold of an amyloid structure. The 13-rung, right-handed, parallel beta-helix of the homotrimeric P22 tailspike adhesin exhibits predominantly hydrophobic stacks. The role of these stacked residues in the folding and stabilization of the protein is unclear. Through scanning alanine mutagenesis we have identified a folding spine of stacked residues in continuous contact along the length of P22 tailspike's beta-helix domain that is necessary for folding within cells. Nearly all chains carrying alanine substitutions of the 103 buried nonalanines were defective in folding in vivo at 37 degrees C. However, the majority of these chains successfully reached a native state, stable to >80 degrees C, when folded inside cells at low temperatures. Thus, nearly the entire buried core was critical for in vivo beta-helix folding but negligible for stability. Folding at 18 degrees C revealed the minimal folding spine of 29 nonglycine stack positions that were intolerant to alanine substitution. These results indicate that a processive folding mechanism, dependent on stacking contacts, controls beta-helix formation. Such a stepwise folding pathway offers a new target for drug design against this class of microbial virulence factors.

Missense meanderings in sequence space: a biophysical view of protein evolution

Proteins are finicky molecules; they are barely stable and are prone to aggregate, but they must function in a crowded environment that is full of degradative enzymes bent on their destruction. It is no surprise that many common diseases are due to missense mutations that affect protein stability and aggregation. Here we review the literature on biophysics as it relates to molecular evolution, focusing on how protein stability and aggregation affect organismal fitness. We then advance a biophysical model of protein evolution that helps us to understand phenomena that range from the dynamics of molecular adaptation to the clock-like rate of protein evolution.

Engineering and characterization of a superfolder green fluorescent protein

Existing variants of green fluorescent protein (GFP) often misfold when expressed as fusions with other proteins. We have generated a robustly folded version of GFP, called 'superfolder' GFP, that folds well even when fused to poorly folded polypeptides. Compared to 'folding reporter' GFP, a folding-enhanced GFP containing the 'cycle-3' mutations and the 'enhanced GFP' mutations F64L and S65T, superfolder GFP shows improved tolerance of circular permutation, greater resistance to chemical denaturants and improved folding kinetics. The fluorescence of Escherichia coli cells expressing each of eighteen proteins from Pyrobaculum aerophilum as fusions with superfolder GFP was proportional to total protein expression. In contrast, fluorescence of folding reporter GFP fusion proteins was strongly correlated with the productive folding yield of the passenger protein. X-ray crystallographic structural analyses helped explain the enhanced folding of superfolder GFP relative to folding reporter GFP.

Twin-arginine signal peptide attributes effective display of CD147 to filamentous phage

A novel phagemid (pTat8) was constructed in this study to improve the quality of a molecule displayed on filamentous phage. The twin-arginine translocation (Tat) pathway was chosen for transporting and integrating a CD147 molecule into a phage particle via gpVIII. The parent vector pComb8-CD147Ex was modified by substituting a Sec signal sequence (PelB) with a twin-arginine signal sequence from trimethylamine N-oxide reductase (TorA). The characteristics of the CD147 displayed on the phage particle were evaluated by Sandwich ELISA and Western immunoblotting. A Tat-dependent leader was found to be superior to the Sec leader for the phage display of CD147. Our findings further support the involvement of an Escherichia coli Tat translocase in mediating the integration of a hydrophobic transmembrane protein into the inner membrane. This modified phagemid will be useful in phage display technique when the correctly folded structure is required (i.e., antibody libraries and ligand-receptor tracing).

Solubilization and refolding of bacterial inclusion body proteins

Inclusion bodies produced in Escherichia coli are composed of densely packed denatured protein molecules in the form of particles. Refolding of inclusion body proteins into bioactive forms is cumbersome, results in poor recovery and accounts for the major cost in production of recombinant proteins from E. coli. With new information available on the structure and function of protein aggregates in bacterial inclusion bodies, it has been possible to develop improved solubilization and refolding procedures for higher recovery of bioactive protein. Inclusion bodies are formed from partially folded protein intermediates and are composed of aggregates of mostly single types of polypeptide. This helps to isolate and purify the protein aggregates to homogeneity before solubilization and refolding. Proteins inside inclusion body aggregates have native-like secondary structures. It is assumed that restoration of this native-like secondary structure using mild solubilization conditions will help in improved recovery of bioactive protein in comparison to solubilization using a high concentration of chaotropic agent. Analysis of the dominant forces causing aggregation during inclusion body formation provides information to develop suitable mild solubilization procedures for inclusion body proteins. Refolding from such solubilized protein will be very high due to restoration of native-like secondary structure. Human growth hormone inclusion bodies were purified to homogeneity from E. coli cells before solubilization and refolding. Pure inclusion bodies were solubilized at alkaline pH in the presence of 2 M urea solution. The solubilized proteins were refolded using a pulsatile renaturation process and subsequently purified using chromatographic procedures. More than 40% of the inclusion body proteins could be refolded back to the bioactive native conformation. Mild solubilization is thus the key for high recovery of bioactive protein from inclusion bodies.