Expression and purification of a cleavable recombinant fortilin from Escherichia coli for structure activity studies.

Complications related to atherosclerosis account for approximately 1 in 4 deaths in the United States and treatment has focused on lowering serum LDL-cholesterol levels with statins. However, approximately 50% of those diagnosed with atherosclerosis have blood cholesterol levels within normal parameters. Human fortilin is an anti-apoptotic protein and a factor in macrophage-mediated atherosclerosis and is hypothesized to protect inflammatory macrophages from apoptosis, leading to subsequent cardiac pathogenesis. Fortilin is unique because it provides a novel drug target for atherosclerosis that goes beyond lowering cholesterol and utilization of a solution nuclear magnetic resonance (NMR) spectroscopy, structure-based drug discovery approach requires milligram quantities of pure, bioactive, recombinant fortilin. Here, we designed expression constructs with different affinity tags and protease cleavage sites to find optimal conditions to obtain the quantity and purity of protein necessary for structure activity relationship studies. Plasmids encoding fortilin with maltose binding protein (MBP), 6-histidine (6His) and glutathione-S-transferase (GST), N- terminal affinity tags were expressed and purified from Escherichia coli (E. coli). Cleavage sites with tobacco etch virus (TEV) protease and human rhinovirus (HRV) 3C protease were assessed. Despite high levels of expression of soluble protein, the fusion constructs were resistant to proteinases without the inclusion of amino acids between the cleavage site and N-terminus. We surveyed constructs with increasing lengths of glycine/serine (GGS) linkers between the cleavage site and fortilin and found that inclusion of at least one GGS insert led to successful protease cleavage and pure fortilin with conserved binding to calcium as measured by NMR.

Center of Biomedical Research Excellence in Matrix Biology: Building Research Infrastructure, Supporting Young Researchers, and Fostering Collaboration.

The Center of Biomedical Research Excellence in Matrix Biology strives to improve our understanding of extracellular matrix at molecular, cellular, tissue, and organismal levels to generate new knowledge about pathophysiology, normal development, and regenerative medicine. The primary goals of the Center are to i) support junior investigators, ii) enhance the productivity of established scientists, iii) facilitate collaboration between both junior and established researchers, and iv) build biomedical research infrastructure that will support research relevant to cell-matrix interactions in disease progression, tissue repair and regeneration, and v) provide access to instrumentation and technical support. A Pilot Project program provides funding to investigators who propose applying their expertise to matrix biology questions. Support from the National Institute of General Medical Sciences at the National Institutes of Health that established the Center of Biomedical Research Excellence in Matrix Biology has significantly enhanced the infrastructure and the capabilities of researchers at Boise State University, leading to new approaches that address disease diagnosis, prevention, and treatment. New multidisciplinary collaborations have been formed with investigators who may not have previously considered how their biomedical research programs addressed fundamental and applied questions involving the extracellular matrix. Collaborations with the broader matrix biology community are encouraged.

Ribbon α-Conotoxin KTM Exhibits Potent Inhibition of Nicotinic Acetylcholine Receptors.

KTM is a 16 amino acid peptide with the sequence WCCSYPGCYWSSSKWC. Here, we present the nuclear magnetic resonance (NMR) structure and bioactivity of this rationally designed α-conotoxin (α-CTx) that demonstrates potent inhibition of rat α3ß2-nicotinic acetylcholine receptors (rα3ß2-nAChRs). Two bioassays were used to test the efficacy of KTM. First, a qualitative PC12 cell-based assay confirmed that KTM acts as a nAChR antagonist. Second, bioactivity evaluation by two-electrode voltage clamp electrophysiology was used to measure the inhibition of rα3ß2-nAChRs by KTM (IC50 = 0.19 ± 0.02 nM), and inhibition of the same nAChR isoform by α-CTx MII (IC50 = 0.35 ± 0.8 nM). The three-dimensional structure of KTM was determined by NMR spectroscopy, and the final set of 20 structures derived from 32 distance restraints, four dihedral angle constraints, and two disulfide bond constraints overlapped with a mean global backbone root-mean-square deviation (RMSD) of 1.7 ± 0.5 Å. The structure of KTM did not adopt the disulfide fold of α-CTx MII for which it was designed, but instead adopted a flexible ribbon backbone and disulfide connectivity of C2-C16 and C3-C8 with an estimated 12.5% α-helical content. In contrast, α-CTx MII, which has a native fold of C2-C8 and C3-C16, has an estimated 38.1% α-helical secondary structure. KTM is the first reported instance of a Framework I (CC-C-C) α-CTx with ribbon connectivity to display sub-nanomolar inhibitory potency of rα3ß2-nAChR subtypes.

Recognition of the 3' splice site RNA by the U2AF heterodimer involves a dynamic population shift.

An essential early step in the assembly of human spliceosomes onto pre-mRNA involves the recognition of regulatory RNA cis elements in the 3' splice site by the U2 auxiliary factor (U2AF). The large (U2AF65) and small (U2AF35) subunits of the U2AF heterodimer contact the polypyrimidine tract (Py-tract) and the AG-dinucleotide, respectively. The tandem RNA recognition motif domains (RRM1,2) of U2AF65 adopt closed/inactive and open/active conformations in the free form and when bound to bona fide Py-tract RNA ligands. To investigate the molecular mechanism and dynamics of 3' splice site recognition by U2AF65 and the role of U2AF35 in the U2AF heterodimer, we have combined single-pair FRET and NMR experiments. In the absence of RNA, the RRM1,2 domain arrangement is highly dynamic on a submillisecond time scale, switching between closed and open conformations. The addition of Py-tract RNA ligands with increasing binding affinity (strength) gradually shifts the equilibrium toward an open conformation. Notably, the protein-RNA complex is rigid in the presence of a strong Py-tract but exhibits internal motion with weak Py-tracts. Surprisingly, the presence of U2AF35, whose UHM domain interacts with U2AF65 RRM1, increases the population of the open arrangement of U2AF65 RRM1,2 in the absence and presence of a weak Py-tract. These data indicate that the U2AF heterodimer promotes spliceosome assembly by a dynamic population shift toward the open conformation of U2AF65 to facilitate the recognition of weak Py-tracts at the 3' splice site. The structure and RNA binding of the heterodimer was unaffected by cancer-linked myelodysplastic syndrome mutants.

Structure-Based Assignment of Ile, Leu, and Val Methyl Groups in the Active and Inactive Forms of the Mitogen-Activated Protein Kinase Extracellular Signal-Regulated Kinase 2.

Resonance assignments are the first step in most NMR studies of protein structure, function, and dynamics. Standard protein assignment methods employ through-bond backbone experiments on uniformly (13)C/(15)N-labeled proteins. For larger proteins, this through-bond assignment procedure often breaks down due to rapid relaxation and spectral overlap. The challenges involved in studies of larger proteins led to efficient methods for (13)C labeling of side chain methyl groups, which have favorable relaxation properties and high signal-to-noise. These methyls are often still assigned by linking them to the previously assigned backbone, thus limiting the applications for larger proteins. Here, a structure-based procedure is described for assignment of (13)C(1)H3-labeled methyls by comparing distance information obtained from three-dimensional methyl-methyl nuclear Overhauser effect (NOE) spectroscopy with the X-ray structure. The Ile, Leu, or Val (ILV) methyl type is determined by through-bond experiments, and the methyl-methyl NOE data are analyzed in combination with the known structure. A hierarchical approach was employed that maps the largest observed "NOE-methyl cluster" onto the structure. The combination of identification of ILV methyl type with mapping of the NOE-methyl clusters greatly simplifies the assignment process. This method was applied to the inactive and active forms of the 42-kDa ILV (13)C(1)H3-methyl labeled extracellular signal-regulated kinase 2 (ERK2), leading to assignment of 60% of the methyls, including 90% of Ile residues. A series of ILV to Ala mutants were analyzed, which helped confirm the assignments. These assignments were used to probe the local and long-range effects of ligand binding to inactive and active ERK2.

Transient electrostatic interactions dominate the conformational equilibrium sampled by multidomain splicing factor U2AF65: a combined NMR and SAXS study.

Multidomain proteins containing intrinsically disordered linkers exhibit large-scale dynamic modes that play key roles in a multitude of molecular recognition and signaling processes. Here, we determine the conformational space sampled by the multidomain splicing factor U2AF65 using complementary nuclear magnetic resonance spectroscopy and small-angle scattering data. Available degrees of conformational freedom are initially stochastically sampled and experimental data then used to delineate the potential energy landscape in terms of statistical probability. The spatial distribution of U2AF65 conformations is found to be highly anisotropic, comprising significantly populated interdomain contacts that appear to be electrostatic in origin. This hypothesis is supported by the reduction of signature PREs reporting on expected interfaces with increasing salt concentration. The described spatial distribution reveals the complete spectrum of the unbound forms of U2AF65 that coexist with the small percentage of a preformed RNA-bound domain arrangement required for polypyrimidine-tract recognition by conformational selection. More generally, the proposed approach to describing conformational equilibria of multidomain proteins can be further combined with other experimental data that are sensitive to domain dynamics.

Next-generation heteronuclear decoupling for high-field biomolecular NMR spectroscopy.

Ultra-high-field NMR spectroscopy requires an increased bandwidth for heteronuclear decoupling, especially in biomolecular NMR applications. Composite pulse decoupling cannot provide sufficient bandwidth at practical power levels, and adiabatic pulse decoupling with sufficient bandwidth is compromised by sideband artifacts. A novel low-power, broadband heteronuclear decoupling pulse is presented that generates minimal, ultra-low sidebands. The pulse was derived using optimal control theory and represents a new generation of decoupling pulses free from the constraints of periodic and cyclic sequences. In comparison to currently available state-of-the-art methods this novel pulse provides greatly improved decoupling performance that satisfies the demands of high-field biomolecular NMR spectroscopy.

Genomic signatures of diet-related shifts during human origins.

There are numerous anthropological analyses concerning the importance of diet during human evolution. Diet is thought to have had a profound influence on the human phenotype, and dietary differences have been hypothesized to contribute to the dramatic morphological changes seen in modern humans as compared with non-human primates. Here, we attempt to integrate the results of new genomic studies within this well-developed anthropological context. We then review the current evidence for adaptation related to diet, both at the level of sequence changes and gene expression. Finally, we propose some ways in which new technologies can help identify specific genomic adaptations that have resulted in metabolic and morphological differences between humans and non-human primates.

Comparative expression analysis of the phosphocreatine circuit in extant primates: Implications for human brain evolution.

While the hominid fossil record clearly shows that brain size has rapidly expanded over the last ~2.5 M.yr. the forces driving this change remain unclear. One popular hypothesis proposes that metabolic adaptations in response to dietary shifts supported greater encephalization in humans. An increase in meat consumption distinguishes the human diet from that of other great apes. Creatine, an essential metabolite for energy homeostasis in muscle and brain tissue, is abundant in meat and was likely ingested in higher quantities during human origins. Five phosphocreatine circuit proteins help regulate creatine utilization within energy demanding cells. We compared the expression of all five phosphocreatine circuit genes in cerebral cortex, cerebellum, and skeletal muscle tissue for humans, chimpanzees, and rhesus macaques. Strikingly, SLC6A8 and CKB transcript levels are higher in the human brain, which should increase energy availability and turnover compared to non-human primates. Combined with other well-documented differences between humans and non-human primates, this allocation of energy to the cerebral cortex and cerebellum may be important in supporting the increased metabolic demands of the human brain.

Repurposing Drugs to Treat Heart and Brain Illness.

Drug development is a complicated, slow and expensive process with high failure rates. One strategy to mitigate these factors is to recycle existing drugs with viable safety profiles and have gained Food and Drug Administration approval following extensive clinical trials. Cardiovascular and neurodegenerative diseases are difficult to treat, and there exist few effective therapeutics, necessitating the development of new, more efficacious drugs. Recent scientific studies have led to a mechanistic understanding of heart and brain disease progression, which has led researchers to assess myriad drugs for their potential as pharmacological treatments for these ailments. The focus of this review is to survey strategies for the selection of drug repurposing candidates and provide representative case studies where drug repurposing strategies were used to discover therapeutics for cardiovascular and neurodegenerative diseases, with a focus on anti-inflammatory processes where new drug alternatives are needed.

Bioactive recombinant human oncostatin M for NMR-based screening in drug discovery.

Oncostatin M (OSM) is a pleiotropic, interleukin-6 family inflammatory cytokine that plays an important role in inflammatory diseases, including inflammatory bowel disease, rheumatoid arthritis, and cancer progression and metastasis. Recently, elevated OSM levels have been found in the serum of COVID-19 patients in intensive care units. Multiple anti-OSM therapeutics have been investigated, but to date no OSM small molecule inhibitors are clinically available. To pursue a high-throughput screening and structure-based drug discovery strategy to design a small molecule inhibitor of OSM, milligram quantities of highly pure, bioactive OSM are required. Here, we developed a reliable protocol to produce highly pure unlabeled and isotope enriched OSM from E. coli for biochemical and NMR studies. High yields (ca. 10 mg/L culture) were obtained in rich and minimal defined media cultures. Purified OSM was characterized by mass spectrometry and circular dichroism. The bioactivity was confirmed by induction of OSM/OSM receptor signaling through STAT3 phosphorylation in human breast cancer cells. Optimized buffer conditions yielded 1H, 15N HSQC NMR spectra with intense, well-dispersed peaks. Titration of 15N OSM with a small molecule inhibitor showed chemical shift perturbations for several key residues with a binding affinity of 12.2 ± 3.9 µM. These results demonstrate the value of bioactive recombinant human OSM for NMR-based small molecule screening.

Flexibility in the Periplasmic Domain of BamA Is Important for Function.

The ß-barrel assembly machine (BAM) mediates the biogenesis of outer membrane proteins (OMPs) in Gram-negative bacteria. BamA, the central BAM subunit composed of a transmembrane ß-barrel domain linked to five polypeptide transport-associated (POTRA) periplasmic domains, is thought to bind nascent OMPs and undergo conformational cycling to catalyze OMP folding and insertion. One model is that conformational flexibility between POTRA domains is part of this conformational cycling. Nuclear magnetic resonance (NMR) spectroscopy was used here to study the flexibility of the POTRA domains 1-5 in solution. NMR relaxation studies defined effective rotational correlational times and together with residual dipolar coupling data showed that POTRA1-2 is flexibly linked to POTRA3-5. Mutants of BamA that restrict flexibility between POTRA2 and POTRA3 by disulfide crosslinking displayed impaired function in vivo. Together these data strongly support a model in which conformational cycling of hinge motions between POTRA2 and POTRA3 in BamA is required for biological function.

Structural model of the amino propeptide of collagen XI alpha1 chain with similarity to the LNS domains.

Fibrillar collagens are the principal structural molecules of connective tissues. The assembly of collagen fibrils is regulated by quantitatively minor fibrillar collagens, types V and XI. A unique amino-terminal propeptide domain of these collagens has been attributed this regulatory role. The structure of the amino terminal propeptide has yet to be determined. Low sequence similarity necessitated a secondary structure-based method to carry out homology modeling based upon the determined structure of LNS family members, named for a common structure in the laminin LG5 domain, the neurexin 1B domain and the sex hormone binding globulin. Distribution of amino acids within the model suggested glycosaminoglycan interaction and calcium binding. These activities were tested experimentally. Sequence analyses of existing genes for collagens indicate that 16 known collagen alpha chains may contain an LNS domain. A similar approach may prove useful for structure/function studies of similar domains in other collagens with similar domains. This will provide mechanistic details of the organization and assembly of the extracellular matrix and the underlying basis of structural integrity in connective tissues. The absolute requirement for collagen XI in skeletal growth is indicated by collagen XI deficiencies such as chondrodystrophies found in the cho/cho mouse and in humans with Stickler syndrome.

Structural Analysis of Protein-RNA Complexes in Solution Using NMR Paramagnetic Relaxation Enhancements.

Biological activity in the cell is predominantly mediated by large multiprotein and protein-nucleic acid complexes that act together to ensure functional fidelity. Nuclear magnetic resonance (NMR) spectroscopy is the only method that can provide information for high-resolution three-dimensional structures and the conformational dynamics of these complexes in solution. Mapping of binding interfaces and molecular interactions along with the characterization of conformational dynamics is possible for very large protein complexes. In contrast, de novo structure determination by NMR becomes very time consuming and difficult for protein complexes larger than 30 kDa as data are noisy and sparse. Fortunately, high-resolution structures are often available for individual domains or subunits of a protein complex and thus sparse data can be used to define their arrangement and dynamics within the assembled complex. In these cases, NMR can therefore be efficiently combined with complementary solution techniques, such as small-angle X-ray or neutron scattering, to provide a comprehensive description of the structure and dynamics of protein complexes in solution. Particularly useful are NMR-derived paramagnetic relaxation enhancements (PREs), which provide long-range distance restraints (ca. 20Å) for structural analysis of large complexes and also report on conformational dynamics in solution. Here, we describe the use of PREs from sample production to structure calculation, focusing on protein-RNA complexes. On the basis of recent examples from our own research, we demonstrate the utility, present protocols, and discuss potential pitfalls when using PREs for studying the structure and dynamic features of protein-RNA complexes.

PREDICTED STRUCTURE AND BINDING MOTIFS OF COLLAGEN α1(XI).

The amino propeptide of collagen α1(XI) (NPP) has been shown to bind glycosaminoglycans and to form a dimer. While these are independent biochemical events, it is likely that dimerization facilitates the interaction with glycosaminoglycans or alternatively, that glycosaminoglycan interaction facilitates the formation of an NPP:NPP dimer. The computer program MODELLER was used to generate a homology model of the collagen α1(XI) NPP monomer using the crystal structure of the closely related noncollagenous-4 (NC4) domain of collagen α1(IX) (PDB:2UUR) as the template. Additionally, a dimer model of collagen α1(XI) NPP domain was created based upon the thrombospondin dimer template (PDB:1Z78). The structure of the dimer created in MODELLER was validated by comparison to a dimer model generated by docking two monomers of PDB:2UUR using ClusPro. Calculations of relative binding energy for the interaction between each collagen α1(XI) NPP model and glycosaminoglycans as ligands was performed using AutoDock4. Computational results support a higher affinity between heparan sulfate and a dimer compared to a monomer. These findings are supported by affinity chromatography experiments in which distinct monomer and dimer peaks were observed. Sequential point mutation studies of the putative binding site (147-KKKITK-152) indicated the importance of the basic lysine residue for binding to heparan sulfate. Two orders of magnitude change in binding affinity was predicted when comparing wild type to the mutation K152A. Experimental data supports the predicted change in affinity.

Structure of the BamC two-domain protein obtained by Rosetta with a limited NMR data set.

The CS-RDC-NOE Rosetta program was used to generate the solution structure of a 27-kDa fragment of the Escherichia coli BamC protein from a limited set of NMR data. The BamC protein is a component of the essential five-protein ß-barrel assembly machine in E. coli. The first 100 residues in BamC were disordered in solution. The Rosetta calculations showed that BamC101₋344 forms two well-defined domains connected by an ~18-residue linker, where the relative orientation of the domains was not defined. Both domains adopt a helix-grip fold previously observed in the Bet v 1 superfamily. ¹5N relaxation data indicated a high degree of conformational flexibility for the linker connecting the N-terminal domain and the C-terminal domain in BamC. The results here show that CS-RDC-NOE Rosetta is robust and has a high tolerance for misassigned nuclear Overhauser effect restraints, greatly simplifying NMR structure determinations.

A pipeline to determine RT-QPCR control genes for evolutionary studies: application to primate gene expression across multiple tissues.

Because many species-specific phenotypic differences are assumed to be caused by differential regulation of gene expression, many recent investigations have focused on measuring transcript abundance. Despite the availability of high-throughput platforms, quantitative real-time polymerase chain reaction (RT-QPCR) is often the method of choice because of its low cost and wider dynamic range. However, the accuracy of this technique heavily relies on the use of multiple valid control genes for normalization. We created a pipeline for choosing genes potentially useful as RT-QPCR control genes for measuring expression between human and chimpanzee samples across multiple tissues, using published microarrays and a measure of tissue-specificity. We identified 13 genes from the pipeline and from commonly used control genes: ACTB, USP49, ARGHGEF2, GSK3A, TBP, SDHA, EIF2B2, GPDH, YWHAZ, HPTR1, RPL13A, HMBS, and EEF2. We then tested these candidate genes and validated their expression stability across species. We established the rank order of the most preferable set of genes for single and combined tissues. Our results suggest that for at least three tissues (cerebral cortex, liver, and skeletal muscle), EIF2B2, EEF2, HMBS, and SDHA are useful genes for normalizing human and chimpanzee expression using RT-QPCR. Interestingly, other commonly used control genes, including TBP, GAPDH, and, especially ACTB do not perform as well. This pipeline could be easily adapted to other species for which expression data exist, providing taxonomically appropriate control genes for comparisons of gene expression among species.

Functional consequences of genetic variation in primates on tyrosine hydroxylase (TH) expression in vitro.

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis, is known to contain naturally occurring genetic variation in it's promoter region that associates with a number of neuropsychological disorders. As such, examining non-coding regions is important for understanding tyrosine hydroxylase function in human health and disease. We examined approximately 2 kb upstream of the translation start site within humans and non-human primates to obtain a fine resolution map of evolutionarily and functionally relevant cis-regulatory differences. Our study investigated Macaca mulatta, Pan troglodytes, Gorilla gorilla, and Homo sapiens haplotypes using transient dual-luciferase transfection in three neuroblastoma cell lines to assay the impact of naturally occurring sequence variation on expression level. In addition to trans effects between cell lines, there are several significant expression differences between primate species, but the most striking difference was seen between human haplotypes in one cell line. Underlying this variation are numerous sequence polymorphisms, two of which influence expression within humans in a non-additive and cell line-specific manner. This study highlights functional consequences of tyrosine hydroxylase genetic variation in primates. Additionally, the results emphasize the importance of examining more than one cell line, the existence of multiple functional variants in a given promoter region and the presence of non-additive cis-interactions.

Characterization of collagenous matrix assembly in a chondrocyte model system.

Collagen is a major component of the newly synthesized pericellular microenvironment of chondrocytes. Collagen types II, IX, and XI are synthesized and assembled into higher ordered complexes by a mechanism in which type XI collagen plays a role in nucleation of new fibrils, and in limiting fibril diameter. This study utilizes a cell line derived from the Swarm rat chondrosarcoma that allows the accumulation and assembly of pericellular matrix. Immunofluorescence and atomic force microscopy were used to assess early intermediates of fibril formation. Results indicate that this cell line synthesizes and secretes chondrocyte-specific pericellular matrix molecules including types II, IX, and XI collagen and is suitable for the study of newly synthesized collagen matrix under the experimental conditions used. AFM data indicate that small fibrils or assemblies of microfibrils are detectable and may represent precursors of the approximately 20 nm thin fibrils reported in cartilage. Treatment with hyaluronidase indicates that the dimensions of the small fibrils may be dependent upon the presence of hyaluronan within the matrix. This study provides information on the composition and organization of the newly synthesized extracellular matrix that plays a role in establishing the material properties and performance of biological materials such as cartilage.

Expression, purification, and refolding of recombinant collagen alpha1(XI) amino terminal domain splice variants.

The amino terminal domain of collagen type XI alpha1 chain is a noncollagenous structure that is essential for the regulation of fibrillogenesis in developing cartilage. The amino terminal domain is alternatively spliced at the mRNA level, resulting in proteins expressed as splice variants. These splice variants, or isoforms, have unique distribution in growing tissues, alluding to distinct roles in development. We report here a rapid and straightforward method for expression, purification and in vitro folding of recombinant collagen XI isoforms alpha1(XI) NTD[p7] and alpha1(XI) NTD[p6b+7]. The recombinant isoforms were expressed in Escherichia coli as bacterial inclusion bodies. Unfolded carboxy terminal polyhistidine tagged proteins were purified via nickel affinity chromatography and refolded with specific protocols optimized for each isoform. Purity was assessed by SDS-PAGE and correct secondary structure by a comparison of circular dichroism data with that obtained for Npp. Protein expression and purification of the recombinant collagen XI splice variants will allow further studies to elucidate the structure and molecular interactions with components of the extracellular matrix. This research will clarify the mechanism of collagen XI mediated regulation of collagen fibrillogenesis.