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Necrotizing enterocolitis (NEC) is the leading cause of morbidity and mortality in premature infants. One of the most devastating complications of NEC is the development of NEC-induced brain injury, which manifests as impaired cognition that persists beyond infancy, and which represents a pro-inflammatory activation of the gut-brain axis. Given that oral administration of the human milk oligosaccharides (HMOs) 2'-fucosyl lactose (2'-FL) or 6'-sialyslactose (6'-SL) significantly reduced intestinal inflammation in mice, we now hypothesize that oral administration of these HMOs will reduce NEC-induced brain injury, and sought to determine the mechanisms involved. We now show that the administration of either 2'-FL or 6'-SL significantly attenuated NEC-induced brain injury, reversed myelin loss in the corpus callosum and midbrain of newborn mice, and prevented the impaired cognition observed in mice with NEC-induced brain injury. In seeking to define the mechanisms involved, 2'-FL or 6'-SL administration resulted in a restoration of the blood-brain barrier in newborn mice, and also had a direct anti-inflammatory effect on the brain as revealed through the study of brain organoids. Metabolites of 2'-FL were detected in the infant mouse brain by Nuclear Magnetic resonance (NMR), whereas intact 2'-FL was not. Strikingly, the beneficial effects of 2'-FL or 6'-SL against NEC-induced brain injury required the release of the neurotrophic factor BDNF, as mice lacking BDNF were not protected by these HMOs from the development of NEC-induced brain injury. These findings reveal that the HMOs 2'-FL or 6'-SL interrupt the gut-brain inflammatory axis and reduce the risk of NEC-induced brain injury.

The putative interaction of a C-F bond with an amide carbonyl has been an intriguing topic of interest in this century for reasons spanning basic physical organic chemistry to biochemistry. However, to date, there exist no examples of a close, well-defined interaction in which its unique aspects can be identified and exploited. Herein, we finally present an engineered system possessing an exceptionally tight C-F-amide interaction, allowing us to obtain spectroscopic, crystallographic, and kinetic details of a distinctive, biochemically relevant chemical system for the first time. In turn, we also explore Lewis acid coordination, C-F bond promotion of amide isomerization, enantiomerization, and ion protonation processes.

Nearly all retroviruses selectively package two copies of their unspliced RNA genomes from a cellular milieu that contains a substantial excess of non-viral and spliced viral RNAs. Over the past four decades, combinations of genetic experiments, phylogenetic analyses, nucleotide accessibility mapping, in silico RNA structure predictions, and biophysical experiments were employed to understand how retroviral genomes are selected for packaging. Genetic studies provided early clues regarding the protein and RNA elements required for packaging, and nucleotide accessibility mapping experiments provided insights into the secondary structures of functionally important elements in the genome. Three-dimensional structural determinants of packaging were primarily derived by nuclear magnetic resonance (NMR) spectroscopy. A key advantage of NMR, relative to other methods for determining biomolecular structure (such as X-ray crystallography), is that it is well suited for studies of conformationally dynamic and heterogeneous systems-a hallmark of the retrovirus packaging machinery. Here, we review advances in understanding of the structures, dynamics, and interactions of the proteins and RNA elements involved in retroviral genome selection and packaging that are facilitated by NMR.

Nearly all retroviruses selectively package two copies of their unspliced RNA genomes from a cellular milieu that contains a substantial excess of non-viral and spliced viral RNAs. Over the past four decades, combinations of genetic experiments, phylogenetic analyses, nucleotide accessibility mapping, in silico RNA structure predictions, and biophysical experiments were employed to understand how retroviral genomes are selected for packaging. Genetic studies provided early clues regarding the protein and RNA elements required for packaging, and nucleotide accessibility mapping experiments provided insights into the secondary structures of functionally important elements in the genome. Three-dimensional structural determinants of packaging were primarily derived by nuclear magnetic resonance (NMR) spectroscopy. A key advantage of NMR, relative to other methods for determining biomolecular structure (such as X-ray crystallography), is that it is well suited for studies of conformationally dynamic and heterogeneous systems—a hallmark of the retrovirus packaging machinery. Here, we review advances in understanding of the structures, dynamics, and interactions of the proteins and RNA elements involved in retroviral genome selection and packaging that are facilitated by NMR.

Bacteroides is a highly abundant taxon in the human gut, and Bacteroides thetaiotaomicron (B. theta) is a ubiquitous human symbiont that colonizes the host early in development and persists throughout its life span. The phenotypic plasticity of keystone organisms such as B. theta is important to understand in order to predict phenotype(s) and metabolic interactions under changing nutrient conditions such as those that occur in complex gut communities. Our study shows B. theta prioritizes energy conservation and suppresses secretion of “overflow metabolites” such as organic acids and amino acids when concentrations of acetate are high. Secreted metabolites, especially amino acids, can be a source of nutrients or signals for the host or other microbes in the community. Our study suggests that when metabolically stressed by acetate, B. theta stops sharing with its ecological partners., Microbial metabolism and trophic interactions between microbes give rise to complex multispecies communities in microbe-host systems. Bacteroides thetaiotaomicron (B. theta) is a human gut symbiont thought to play an important role in maintaining host health. Untargeted nuclear magnetic resonance metabolomics revealed B. theta secretes specific organic acids and amino acids in defined minimal medium. Physiological concentrations of acetate and formate found in the human intestinal tract were shown to cause dose-dependent changes in secretion of metabolites known to play roles in host nutrition and pathogenesis. While secretion fluxes varied, biomass yield was unchanged, suggesting feedback inhibition does not affect metabolic bioenergetics but instead redirects carbon and energy to CO2 and H2. Flux balance analysis modeling showed increased flux through CO2-producing reactions under glucose-limiting growth conditions. The metabolic dynamics observed for B. theta, a keystone symbiont organism, underscores the need for metabolic modeling to complement genomic predictions of microbial metabolism to infer mechanisms of microbe-microbe and microbe-host interactions. IMPORTANCE Bacteroides is a highly abundant taxon in the human gut, and Bacteroides thetaiotaomicron (B. theta) is a ubiquitous human symbiont that colonizes the host early in development and persists throughout its life span. The phenotypic plasticity of keystone organisms such as B. theta is important to understand in order to predict phenotype(s) and metabolic interactions under changing nutrient conditions such as those that occur in complex gut communities. Our study shows B. theta prioritizes energy conservation and suppresses secretion of “overflow metabolites” such as organic acids and amino acids when concentrations of acetate are high. Secreted metabolites, especially amino acids, can be a source of nutrients or signals for the host or other microbes in the community. Our study suggests that when metabolically stressed by acetate, B. theta stops sharing with its ecological partners.

NMR has provided a wealth of structural and dynamical information for RNA molecules of up to ∼50 nucleotides, but its application to larger RNAs has been hampered in part by difficulties establishing global structural features. A potential solution involves measurement of NMR perturbations after site-specific paramagnetic labeling. Although the approach works well for proteins, the inability to place the label at specific sites has prevented its application to larger RNAs transcribed in vitro. Here, we present a strategy in which RNA loop residues are modified to promote binding to a paramagnetically tagged reporter protein. Lanthanide-induced pseudocontact shifts are demonstrated for a 232-nucleotide RNA bound to tagged derivatives of the spliceosomal U1A RNA-binding domain. Further, the method is validated with a 36-nucleotide RNA for which measured NMR values agreed with predictions based on the previously known protein and RNA structures. The ability to readily insert U1A binding sites into ubiquitous hairpin and/or loop structures should make this approach broadly applicable for the atomic-level study of large RNAs.

The rapid emergence of resistant bacterial strains has made the search for new antibacterial agents an endeavor of paramount importance. Cationic antimicrobial peptides (AMPs) have the ability to kill resistant pathogens while diminishing the development of resistance. Citropin 1.1 (Cit 1.1) is an AMP effective against a broad range of pathogens. 20 analogues of Cit 1.1 were prepared to understand how sequence variations lead to changes in structure and biological activity. Various analogues exhibited an increased antimicrobial activity relative to Cit 1.1. The two most promising, AMP-016 (W3F) and AMP-017 (W3F, D4R, K7R) presented a 2- to 8-fold increase in activity against MRSA (both = 4 μg/mL). AMP-017 was active against E. coli (4 μg/mL), K. pneumoniae (8 μg/mL), and A. baumannii (2 μg/mL). NMR studies indicated that Cit 1.1 and its analogues form a head-to-tail helical dimer in a membrane environment, which differs from a prior study by Sikorska et al. Active peptides displayed a greater tendency to form α-helices and to dimerize when in contact with a negatively-charged membrane. Antimicrobial activity was observed to correlate to the overall stability of the α-helix and to a positively charged N-terminus. Biologically active AMPs were shown by SEM and flow cytometry to disrupt membranes in both Gram-positive and Gram-negative bacteria through a proposed carpet mechanism. Notably, active peptides exhibited typical serum stabilities and a good selectivity for bacterial cells over mammalian cells, which supports the potential use of Cit 1.1 analogues as a novel broad-spectrum antibiotic for drug-resistant bacterial infections.

Protein function elucidation often relies heavily on amino acid sequence analysis and other bioinformatics approaches. The reliance is extended to structure homology modeling for ligand docking and protein-protein interaction mapping. However, sequence analysis of RPA3313 exposes a large, unannotated class of hypothetical proteins mostly from the Rhizobiales order. In the absence of sequence and structure information, further functional elucidation of this class of proteins has been significantly hindered. A high quality NMR structure of RPA3313 reveals that the protein forms a novel split ββαβ fold with a conserved ligand binding pocket between the first β-strand and the N-terminus of the α-helix. Conserved residue analysis and protein-protein interaction prediction analyses reveal multiple protein binding sites and conserved functional residues. Results of a mass spectrometry proteomic analysis strongly point toward interaction with the ribosome and its subunits. The combined structural and proteomic analyses suggest that RPA3313 by itself or in a larger complex may assist in the transportation of substrates to or from the ribosome for further processing. This article is protected by copyright. All rights reserved.

The functional evolution of proteins advances through gene duplication followed by functional drift, whereas molecular evolution occurs through random mutational events. Over time, protein active-site structures or functional epitopes remain highly conserved, which enables relationships to be inferred between distant orthologs or paralogs. In this study, we present the first functional clustering and evolutionary analysis of the RCSB Protein Data Bank (RCSB PDB) based on similarities between active-site structures. All of the ligand-bound proteins within the RCSB PDB were scored using our Comparison of Protein Active-site Structures (CPASS) software and database (http://cpass.unl.edu/). Principal component analysis was then used to identify 4,431 representative structures to construct a phylogenetic tree based on the CPASS comparative scores (http://itol.embl.de/shared/jcatazaro). The resulting phylogenetic tree identified a sequential, step-wise evolution of protein active-sites and provides novel insights into the emergence of protein function or changes in substrate specificity based on subtle changes in geometry and amino acid composition.

Various missense mutations in the cytoprotective protein DJ-1 cause rare forms of inherited parkinsonism. One mutation, M26I, diminishes DJ-1 protein levels in the cell but does not result in large changes in the three-dimensional structure or thermal stability of the protein. Therefore, the molecular defect that results in loss of M26I DJ-1 protective function is unclear. Using NMR spectroscopy near physiological temperature, we found that the picosecond–nanosecond dynamics of wild-type and M26I DJ-1 are similar. In contrast, elevated amide hydrogen/deuterium exchange rates indicate that M26I DJ-1 is more flexible than the wild-type protein on longer timescales and that hydrophobic regions of M26I DJ-1 are transiently exposed to solvent. Tryptophan fluorescence spectroscopy and thiol crosslinking analyzed by mass spectrometry also demonstrate that M26I DJ-1 samples conformations that differ from the wild-type protein at 37°C. These transiently sampled conformations are unstable and cause M26I DJ-1 to aggregate in vitro at physiological temperature but not at lower temperatures. M26I DJ-1 aggregation is correlated with pathogenicity, as the structurally similar but non-pathogenic M26L mutation does not aggregate at 37°C. The onset of dynamically driven M26I DJ-1 instability at physiological temperature resolves conflicting literature reports about the behavior of this disease-associated mutant and illustrates the pitfalls of characterizing proteins exclusively at room temperature or below, as key aspects of their behavior may not be apparent.

Previous studies have shown that relaxation parameters and fast protein dynamics can be quickly elucidated from 15N-CEST experiments [1]. Longitudinal R1 and transverse R2 values were reliably derived from fitting of CEST profiles. Herein we show that 15N-CEST experiments and traditional modelfree analysis provide the internal dynamics of three states of human protein DJ-1 at physiological temperature. The chemical exchange profiles show the absence of a minor state conformation and, in conjunction with 1H-15N NOEs, show increased mobility. R1 and R2 values remained relatively unchanged at the three naturally occurring oxidation states of DJ-1, but exhibit striking NOE differences. The NOE data was, therefore, essential in determining the internal motions of the DJ-1 proteins. To the authors' knowledge, we present the first study that combines 15N CEST data with traditional model-free analyses in the study of a biological system and affirm that more 'lean' model-free approaches should be used cautiously.

The Warburg effect is a predominant metabolic pathway in cancer cells characterized by enhanced glucose uptake and its conversion to l-lactate and is associated with upregulated expression of HIF-1α and activation of the EGFR-MEK-ERK, Wnt-β-catenin, and PI3K-AKT signaling pathways. (R,R')-4'-methoxy-1-naphthylfenoterol ((R,R')-MNF) significantly reduces proliferation, survival, and motility of PANC-1 pancreatic cancer cells through inhibition of the GPR55 receptor. We examined (R,R')-MNF's effect on glycolysis in PANC-1 cells and tumors. Global NMR metabolomics was used to elucidate differences in the metabolome between untreated and (R,R')-MNF-treated cells. LC/MS analysis was used to quantify intracellular concentrations of β-hydroxybutyrate, carnitine, and l-lactate. Changes in target protein expression were determined by Western blot analysis. Data was also obtained from mouse PANC-1 tumor xenografts after administration of (R,R')-MNF. Metabolomics data indicate that (R,R')-MNF altered fatty acid metabolism, energy metabolism, and amino acid metabolism and increased intracellular concentrations of β-hydroxybutyrate and carnitine while reducing l-lactate content. The cellular content of phosphoinositide-dependent kinase-1 and hexokinase 2 was reduced consistent with diminished PI3K-AKT signaling and glucose metabolism. The presence of the GLUT8 transporter was established and found to be attenuated by (R,R')-MNF. Mice treated with (R,R')-MNF had significant accumulation of l-lactate in tumor tissue relative to vehicle-treated mice, together with reduced levels of the selective l-lactate transporter MCT4. Lower intratumoral levels of EGFR, pyruvate kinase M2, β-catenin, hexokinase 2, and p-glycoprotein were also observed. The data suggest that (R,R')-MNF reduces glycolysis in PANC-1 cells and tumors through reduced expression and function at multiple controlling sites in the glycolytic pathway.

Families of distantly related proteins typically have very low sequence identity, which hinders evolutionary analysis and functional annotation. Slowly evolving features of proteins, such as an active site, are therefore valuable for annotating putative and distantly related proteins. To date, a complete evolutionary analysis of the functional relationship of an entire enzyme family based on active-site structural similarities has not yet been undertaken. Pyridoxal-5'-phosphate (PLP) dependent enzymes are primordial enzymes that diversified in the last universal ancestor. Using the comparison of protein active site structures (CPASS) software and database, we show that the active site structures of PLP-dependent enzymes can be used to infer evolutionary relationships based on functional similarity. The enzymes successfully clustered together based on substrate specificity, function, and three-dimensional-fold. This study demonstrates the value of using active site structures for functional evolutionary analysis and the effectiveness of CPASS.

The Warburg effect is a predominant metabolic pathway in cancer cells characterized by enhanced glucose uptake and its conversion to l-lactate and is associated with upregulated expression of HIF-1α and activation of the EGFR-MEK-ERK, Wnt-β-catenin, and PI3K-AKT signaling pathways. (R,R')-4'-methoxy-1-naphthylfenoterol ((R,R')-MNF) significantly reduces proliferation, survival, and motility of PANC-1 pancreatic cancer cells through inhibition of the GPR55 receptor. We examined (R,R')-MNF's effect on glycolysis in PANC-1 cells and tumors. Global NMR metabolomics was used to elucidate differences in the metabolome between untreated and (R,R')-MNF-treated cells. LC/MS analysis was used to quantify intracellular concentrations of β-hydroxybutyrate, carnitine, and l-lactate. Changes in target protein expression were determined by Western blot analysis. Data was also obtained from mouse PANC-1 tumor xenografts after administration of (R,R')-MNF. Metabolomics data indicate that (R,R')-MNF altered fatty acid metabolism, energy metabolism, and amino acid metabolism and increased intracellular concentrations of β-hydroxybutyrate and carnitine while reducing l-lactate content. The cellular content of phosphoinositide-dependent kinase-1 and hexokinase 2 was reduced consistent with diminished PI3K-AKT signaling and glucose metabolism. The presence of the GLUT8 transporter was established and found to be attenuated by (R,R')-MNF. Mice treated with (R,R')-MNF had significant accumulation of l-lactate in tumor tissue relative to vehicle-treated mice, together with reduced levels of the selective l-lactate transporter MCT4. Lower intratumoral levels of EGFR, pyruvate kinase M2, β-catenin, hexokinase 2, and p-glycoprotein were also observed. The data suggest that (R,R')-MNF reduces glycolysis in PANC-1 cells and tumors through reduced expression and function at multiple controlling sites in the glycolytic pathway.

The interface between the DnaG primase C-terminal domain (CTD) and the N-terminal domain of DnaB helicase is essential for bacterial DNA replication because it allows coordinated priming of DNA synthesis at the replication fork while the DNA is being unwound. Since these two proteins are conserved in all bacteria and distinct from those in eukaryotes, their interface is an attractive antibiotic target. To learn more about this interface, we determined the solution structure and dynamics of the DnaG primase CTD from Staphylococcus aureus, a medically important bacterial species. It has two subdomains like the primase CTD structures from other bacteria in which the first six helices create the C1 subdomain and the last two helices, 7 and 8, create the C2 subdomain. Comparison with the known primase CTD structures shows there are two biologically relevant conformations – an open conformation that likely binds to DnaB helicase and a closed conformation that does not. The S. aureus primase CTD is in the closed conformation, but NMR dynamic studies indicates there is considerable movement in the linker between the two subdomains and that N564 is the most dynamic residue within the linker. A high-throughput NMR ligand-affinity screen identified potential binding compounds, among which were acycloguanosine and myricetin. Although the affinity for these compounds and adenosine was in the millimolar range, all three bind to a common pocket that is only present on the closed conformation of CTD. This binding pocket is at the opposite end of helices 6 and 7 from N564, the key hinge residue. The identification of this binding pocket should allow the development of stronger-binding ligands that can prevent formation of the CTD open conformation that binds to DnaB helicase.

Various missense mutations in the cytoprotective protein DJ-1 cause rare forms of inherited parkinsonism. One mutation, M26I, diminishes DJ-1 protein levels in the cell but does not result in large changes in the three-dimensional structure or thermal stability of the protein. Therefore, the molecular defect that results in loss of M26I DJ-1 protective function is unclear. Using NMR spectroscopy near physiological temperature, we found that the picosecond–nanosecond dynamics of wild-type and M26I DJ-1 are similar. In contrast, elevated amide hydrogen/deuterium exchange rates indicate that M26I DJ-1 is more flexible than the wild-type protein on longer timescales and that hydrophobic regions of M26I DJ-1 are transiently exposed to solvent. Tryptophan fluorescence spectroscopy and thiol crosslinking analyzed by mass spectrometry also demonstrate that M26I DJ-1 samples conformations that differ from the wild-type protein at 37°C. These transiently sampled conformations are unstable and cause M26I DJ-1 to aggregate in vitro at physiological temperature but not at lower temperatures. M26I DJ-1 aggregation is correlated with pathogenicity, as the structurally similar but non-pathogenic M26L mutation does not aggregate at 37°C. The onset of dynamically driven M26I DJ-1 instability at physiological temperature resolves conflicting literature reports about the behavior of this disease-associated mutant and illustrates the pitfalls of characterizing proteins exclusively at room temperature or below, as key aspects of their behavior may not be apparent.

We have recently demonstrated that (R,R’)-4′-methoxy-1-naphthylfenoterol (MNF) significantly reduces proliferation in pancreatic cancer (PancCA) cell lines, including PANC-1. MNF is a potent competitive inhibitor of the G-protein coupled receptor GPR55 and the anti-proliferative effects in PANC-1 cells was associated with down-stream events including attenuation of epidermal growth factor receptor (EGFR) expression and reduced phosphorylation of extracellular signal-related kinases [1]. In the current study, a previously described untargeted metabolomics approach using one-dimensional proton nuclear magnetic resonance (1D 1H NMR) [2] was used to examine the effect of MNF incubation (1 μM, 1h) on the intracellular metabolome of PANC-1 cells. Principal component analysis showed that MNF incubation produced a significantly different metabolome as compared to untreated cells. MNF treatment significantly reduced the signal associated with lactate indicating impaired glycolysis. Enhanced aerobic glycolysis in tumor cells, known as “the Warburg effect”, is a major metabolic contributor to cancer cell proliferation including PancCA [3]. Treatment of PANC-1 cells with the glycolysis inhibitor 3-bromopyruvate lowers cellular survival [4] and co-incubation of 3-bromopyruvate with the HSP90 inhibitor geldanamycin has a positive synergistic anticancer effect in vitro and in vivo [5]. Here, we showed metabolomics data that indicated also an increase in the relative expression of 3-hydroxybutyrate in response to MNF. Supplementation with ketone bodies such as 3-hydroxybutyrate has been associated with decreased proliferation and viability of PancCA cells in vitro and in vivo as well as tumor-related cachexia [1]. The signals associated with leucine, lysine, glycine and carnitine were also significantly upregulated with MNF treatment, indicating a possible role of fatty acid metabolism in MNF signaling. The data suggest that in addition to attenuating EGFR expression and reducing phosphorylation of extracellular signal-related kinases, MNF may affect PANC-1 cell proliferation and survival by disrupting glycolysis. Ref: 1. Paul RK, et.al. (R,R’)-4′-methoxy-1-naphthylfenoterol targets GPR55-mediated ligand internalization and impairs cancer cell motility. Biochem Pharmacol. 2014;87(4):547-61. 2. Shukla SK, et.al. Metabolic Reprogramming Induced by Ketone Bodies Diminishes Pancreatic Cancer Cachexia. Cancer Metab. 2014;2:18. 3. Warburg, O. On the origin of cancer cells. Science. 1956;123:309-14. 4. Bhardwaj V, et.al. Glycolytic enzyme inhibitors affect pancreatic cancer survival by modulating its signaling and energetics. Anticancer Res. 2010;30:743-9. 5. Cao X, et.al. 2008. Synergistic antipancreatic tumor effect by simultaneously targeting hypoxic cancer cells with HSP90 inhibitor and glycolysis inhibitor. Clin Cancer Res.14:1831-9. Citation Format: Nagendra S. Singh, Jonathan Catazaro, Michel Bernier, Robert Powers, Irving Wainer. (R,R’)-4′-Methoxy-1-naphthylfenoterol decreases glycolytic activity in the PANC-1 pancreatic cancer cell line. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1172. doi:10.1158/1538-7445.AM2015-1172