Project description:Flagella are crucial for bacterial motility and pathogenesis. The flagellar capping protein (FliD) regulates filament assembly by chaperoning and sorting flagellin (FliC) proteins after they traverse the hollow filament and exit the growing flagellum tip. In the absence of FliD, flagella are not formed, resulting in impaired motility and infectivity. Here, we report the 2.2 Å resolution X-ray crystal structure of FliD from Pseudomonas aeruginosa, the first high-resolution structure of any FliD protein from any bacterium. Using this evidence in combination with a multitude of biophysical and functional analyses, we find that Pseudomonas FliD exhibits unexpected structural similarity to other flagellar proteins at the domain level, adopts a unique hexameric oligomeric state, and depends on flexible determinants for oligomerization. Considering that the flagellin filaments on which FliD oligomers are affixed vary in protofilament number between bacteria, our results suggest that FliD oligomer stoichiometries vary across bacteria to complement their filament assemblies.
Project description:We introduce AlphaFold-NMR, a novel approach to NMR structure determination that reveals previously undetected protein conformational states. Unlike conventional NMR methods that rely on NOE-derived spatial restraints, AlphaFold-NMR combines AI-driven conformational sampling with Bayesian scoring of realistic protein models against NOESY and chemical shift data. This method uncovers alternative conformational states of the enzyme Gaussia luciferase, involving large-scale changes in the lid, binding pockets, and other surface cavities. It also identifies similar yet distinct conformational states of the human tumor suppressor Cyclin-Dependent Kinase 2-Associated Protein 1. These studies demonstrate the potential of AI-based modeling with enhanced sampling to generate diverse structural models followed by conformer selection and validation with experimental data as an alternative to traditional restraint-satisfaction protocols for protein NMR structure determination. The AlphaFold-NMR framework enables discovery of conformational heterogeneity and cryptic pockets that conventional NMR analysis methods do not distinguish, providing new insights into protein structure-function relationships.
Project description:Head-to-tail cyclic and disulfide-rich peptides are natural products with applications in drug design. Among these are the PawS-Derived Peptides (PDPs) produced in seeds of the daisy plant family. PDP-23 is a unique member of this class in that it is twice the typical size and adopts two β-hairpins separated by a hinge region. The β-hairpins, both stabilised by a single disulfide bond, fold together into a V-shaped tertiary structure creating a hydrophobic core. In water two PDP-23 molecules merge their hydrophobic cores to form a square prism quaternary structure. Here, we synthesised PDP-23 and its enantiomer comprising d-amino acids and achiral glycine, which allowed us to confirm these solution NMR structural data by racemic crystallography. Furthermore, we discovered the related PDP-24. NMR analysis showed that PDP-24 does not form a dimeric structure and it has poor water solubility, but in less polar solvents adopts near identical secondary and tertiary structure to PDP-23. The natural role of these peptides in plants remains enigmatic, as we did not observe any antimicrobial or insecticidal activity. However, the plasticity of these larger PDPs and their ability to change structure under different conditions make them appealing peptide drug scaffolds.
Project description:Ribosome-footprint profiling provides genome-wide snapshots of translation, but technical challenges can confound its analysis. Here, we use improved methods to obtain ribosome-footprint profiles and mRNA abundances that more faithfully reflect gene expression in Saccharomyces cerevisiae. Our results support proposals that both the beginning of coding regions and codons matching rare tRNAs are more slowly translated. They also indicate that emergent polypeptides with as few as three basic residues within a 10-residue window tend to slow translation. With the improved mRNA measurements, the variation attributable to translational control in exponentially growing yeast was less than previously reported, and most of this variation could be predicted with a simple model that considered mRNA abundance, upstream open reading frames, cap-proximal structure and nucleotide composition, and lengths of the coding and 5'-untranslated regions. Collectively, our results provide a framework for executing and interpreting ribosome-profiling studies and reveal key features of translational control in yeast. Ribosome-footprint profiling and RNA-seq (total RNA, poly(A) selected, RiboMinus treated, or Ribo-Zero treated) from log-phase S. cerevisiae. The study includes a reanalysis of the two Samples from GSE53313. The reanalyzed data is linked to the Series record.
Project description:Ribosome-footprint profiling provides genome-wide snapshots of translation, but technical challenges can confound its analysis. Here, we use improved methods to obtain ribosome-footprint profiles and mRNA abundances that more faithfully reflect gene expression in Saccharomyces cerevisiae. Our results support proposals that both the beginning of coding regions and codons matching rare tRNAs are more slowly translated. They also indicate that emergent polypeptides with as few as three basic residues within a 10-residue window tend to slow translation. With the improved mRNA measurements, the variation attributable to translational control in exponentially growing yeast was less than previously reported, and most of this variation could be predicted with a simple model that considered mRNA abundance, upstream open reading frames, cap-proximal structure and nucleotide composition, and lengths of the coding and 5'-untranslated regions. Collectively, our results provide a framework for executing and interpreting ribosome-profiling studies and reveal key features of translational control in yeast.
Project description:The Shigella flexneri Type III secretion system (T3SS) senses contact with human intestinal cells and injects effector proteins that promote pathogen entry as the first step in causing life threatening bacillary dysentery (shigellosis). The Shigella Type III secretion apparatus (T3SA) consists of an anchoring basal body, an exposed needle, and a temporally assembled tip complex. Exposure to environmental small molecules recruits IpaB, the first hydrophobic translocator protein, to the maturing tip complex. IpaB then senses contact with a host cell membrane, forming the translocon pore through which effectors are delivered to the host cytoplasm. Within the bacterium, IpaB exists as a heterodimer with its chaperone IpgC; however, IpaB's structural state following secretion is unknown due to difficulties isolating stable protein. We have overcome this by coexpressing the IpaB/IpgC heterodimer and isolating IpaB by incubating the complex in mild detergents. Interestingly, preparation of IpaB with n-octyl-oligo-oxyethylene (OPOE) results in the assembly of discrete oligomers while purification in N,N-dimethyldodecylamine N-oxide (LDAO) maintains IpaB as a monomer. In this study, we demonstrate that IpaB tetramers penetrate phospholipid membranes to allow a size-dependent release of small molecules, suggesting the formation of discrete pores. Monomeric IpaB also interacts with liposomes but fails to disrupt them. From these and additional findings, we propose that IpaB can exist as a tetramer having inherent flexibility, which allows it to cooperatively interact with and insert into host cell membranes. This event may then lay the foundation for formation of the Shigella T3SS translocon pore.
Project description:BackgroundThe plant immune system employs intracellular NLRs (nucleotide binding [NB], leucine-rich repeat [LRR]/nucleotide-binding oligomerization domain [NOD]-like receptors) to detect effector proteins secreted into the plant cell by potential pathogens. Activated plant NLRs trigger a range of immune responses, collectively known as the hypersensitive response (HR), which culminates in death of the infected cell. Plant NLRs show structural and functional resemblance to animal NLRs involved in inflammatory and innate immune responses. Therefore, knowledge of the activation and regulation of animal NLRs can help us understand the mechanism of action of plant NLRs, and vice versa.ScopeThis review provides an overview of the innate immune pathways in plants and animals, focusing on the available structural and biochemical information available for both plant and animal NLRs. We highlight the gap in knowledge between the animal and plant systems, in particular the lack of structural information for plant NLRs, with crystal structures only available for the N-terminal domains of plant NLRs and an integrated decoy domain, in contrast to the more complete structures available for animal NLRs. We assess the similarities and differences between plant and animal NLRs, and use the structural information on the animal NLR pair NAIP/NLRC4 to derive a plausible model for plant NLR activation.ConclusionsSignalling by cooperative assembly formation (SCAF) appears to operate in most innate immunity pathways, including plant and animal NLRs. Our proposed model of plant NLR activation includes three key steps: (1) initially, the NLR exists in an inactive auto-inhibited state; (2) a combination of binding by activating elicitor and ATP leads to a structural rearrangement of the NLR; and (3) signalling occurs through cooperative assembly of the resistosome. Further studies, structural and biochemical in particular, will be required to provide additional evidence for the different features of this model and shed light on the many existing variations, e.g. helper NLRs and NLRs containing integrated decoys.
Project description:The four human Argonaute (AGO) proteins, critical in RNA interference and gene regulation, exhibit high sequence and structural similarity but differ functionally. We investigated the underexplored structural relationships of these paralogs through microsecond-scale molecular dynamics simulations. Our findings reveal that AGO proteins adopt similar, yet unsynchronized, open-close states. We observed similar and unique local conformations, interdomain distances and intramolecular interactions. Conformational differences at GW182/ZSWIM8 interaction sites and in catalytic/pseudo-catalytic tetrads were minimal. Tetrads display conserved movements, interacting with distant miRNA binding residues. We pinpointed long common protein subsequences with consistent molecular movement but varying solvent accessibility per AGO. We observed diverse conformational patterns at the post-transcriptional sites of the AGOs, except for AGO4. By combining simulation data with large datasets of experimental structures and AlphaFold's predictions, we identified proteins with genomic and proteomic similarities. Some of the identified proteins operate in the mitosis pathway, sharing mitosis-related interactors and miRNA targets. Additionally, we suggest that AGOs interact with a mitosis initiator, zinc ion, by predicting potential binding sites and detecting structurally similar proteins with the same function. These findings further advance our understanding for the human AGO protein family and their role in central cellular processes.
Project description:BackgroundBlood pressure (BP) measurement error may lead to under- or overtreatment of hypertension. One common source of error is terminal digit preference, most often a terminal digit of "0." The objective was to evaluate national trends in terminal digit preference in office BP measurements among adults with treated hypertension.MethodsData were from IQVIA's National Disease and Therapeutic Index, a nationally representative, serial cross-sectional survey of office-based physicians. The analysis included office visits from 2015 to 2019 among adults aged ≥18 years receiving antihypertensive treatment. Annual trends were examined in the percent of systolic and diastolic BP measurements ending in zero by patient sex, age, and race/ethnicity, physician specialty, and first or subsequent hypertension treatment visit.ResultsFrom 2015 to 2019, there were ~60 million hypertension treatment visits annually (unweighted N: 5,585-9,085). There was a decrease in the percent of visits with systolic (41.7%-37.7%) or diastolic (42.7%-37.8%) BP recordings ending in zero. Trends were similar by patient characteristics. However, a greater proportion of measurements ended in zero among patients aged ≥80 (vs. 15-59 or 60-79) years, first (vs. subsequent) treatment visits, visits to cardiologists (vs. primary care physicians), and visits with systolic BP ≥140 or diastolic BP ≥90 (vs. <140/90) mm Hg.ConclusionsDespite modest improvement, terminal digit preference remains a common problem in office BP measurement in the United States. Without bias, 10%-20% of measurements are expected to end in zero. Reducing digit preference is a priority for improving BP measurement accuracy and hypertension management.
Project description:Protein glycosylation is important in many organisms for proper protein folding, signaling, cell adhesion, protein-protein interactions, and immune responses. Thus, effectively determining the extent of glycosylation in glycoprotein therapeutics is crucial. Up to now, characterizing protein glycosylation has been carried out mostly by liquid chromatography mass spectrometry (LC-MS), which requires careful sample processing, e.g., glycan removal or protein digestion and glycopeptide enrichment. Herein, we introduce an NMR-based method to better characterize intact glycoproteins in natural abundance. This non-destructive method relies on exploiting differences in nuclear relaxation to suppress the NMR signals of the protein while maintaining glycan signals. Using RNase B Man5 and RNase B Man9, we establish reference spectra that can be used to determine the different glycoforms present in heterogeneously glycosylated commercial RNase B.