Discordant Antigenic Properties of Soluble and Virion SARS-CoV-2 Spike Proteins

Efforts to develop vaccine and immunotherapeutic countermeasures against the COVID-19 pandemic focus on targeting the trimeric spike (S) proteins of SARS-CoV-2. Vaccines and therapeutic design strategies must impart the characteristics of virion S from historical and emerging variants onto practical constructs such as soluble, stabilized trimers. The virus spike is a heterotrimer of two subunits: S1, which includes the receptor binding domain (RBD) that binds the cell surface receptor ACE2, and S2, which mediates membrane fusion. Previous studies suggest that the antigenic, structural, and functional characteristics of virion S may differ from current soluble surrogates. For example, it was reported that certain anti-glycan, HIV-1 neutralizing monoclonal antibodies bind soluble SARS-CoV-2 S but do not neutralize SARS-CoV-2 virions. In this study, we used single-molecule fluorescence correlation spectroscopy (FCS) under physiologically relevant conditions to examine the reactivity of broadly neutralizing and non-neutralizing anti-S human monoclonal antibodies (mAbs) isolated in 2020. Binding efficiency was assessed by FCS with soluble S trimers, pseudoviruses and inactivated wild-type virions representing variants emerging from 2020 to date. Anti-glycan mAbs were tested and compared. We find that both anti-S specific and anti-glycan mAbs exhibit variable but efficient binding to a range of stabilized, soluble trimers. Across mAbs, the efficiencies of soluble S binding were positively correlated with reactivity against inactivated virions but not pseudoviruses. Binding efficiencies with pseudoviruses were generally lower than with soluble S or inactivated virions. Among neutralizing mAbs, potency did not correlate with binding efficiencies on any target. No neutralizing activity was detected with anti-glycan antibodies. Notably, the virion S released from membranes by detergent treatment gained more efficient reactivity with anti-glycan, HIV-neutralizing antibodies but lost reactivity with all anti-S mAbs. Collectively, the FCS binding data suggest that virion surfaces present appreciable amounts of both functional and nonfunctional trimers, with neutralizing anti-S favoring the former structures and non-neutralizing anti-glycan mAbs binding the latter. S released from solubilized virions represents a nonfunctional structure bound by anti-glycan mAbs, while engineered soluble trimers present a composite structure that is broadly reactive with both mAb types. The detection of disparate antigenicity and immunoreactivity profiles in engineered and virion-associated S highlight the value of single-virus analyses in designing future antiviral strategies against SARS-CoV-2.

Structural determination of Rickettsia lipid A without chemical extraction confirms shorter acyl chains in later-evolving spotted fever group pathogens

Rickettsiae are Gram-negative obligate intracellular parasites of numerous eukaryotes. Human pathogens of the transitional group (TRG), typhus group (TG), and spotted fever group (SFG) rickettsiae infect blood-feeding arthropods, have dissimilar clinical manifestations, and possess unique genomic and morphological attributes. Lacking glycolysis, rickettsiae pilfer numerous metabolites from the host cytosol to synthesize peptidoglycan and lipopolysaccharide (LPS). For LPS, O-antigen immunogenicity varies between SFG and TG pathogens; however, lipid A proinflammatory potential is unknown. We previously demonstrated that Rickettsia akari (TRG), Rickettsia typhi (TG), and Rickettsia montanensis (SFG) produce lipid A with long 2' secondary acyl chains (C16 or C18) compared to short 2' secondary acyl chains (C12) in Rickettsia rickettsii (SFG) lipid A. To further probe this structural heterogeneity and estimate a time point when shorter 2' secondary acyl chains originated, we generated lipid A structures for two additional SFG rickettsiae (Rickettsia rhipicephali and Rickettsia parkeri) utilizing fast lipid analysis technique adopted for use with tandem mass spectrometry (FLATn). FLATn allowed analysis of lipid A structure directly from host cell-purified bacteria, providing a substantial improvement over lipid A chemical extraction. FLATn-derived structures indicate SFG rickettsiae diverging after R. rhipicephali evolved shorter 2' secondary acyl chains. While 2' secondary acyl chain lengths do not distinguish Rickettsia pathogens from non-pathogens, in silico analyses of Rickettsia LpxL late acyltransferases revealed discrete active sites and hydrocarbon rulers for long versus short 2' secondary acyl chain addition. Our collective data warrant determining Rickettsia lipid A inflammatory potential and how structural heterogeneity impacts lipid A-host receptor interactions.IMPORTANCEDeforestation, urbanization, and homelessness lead to spikes in Rickettsioses. Vector-borne human pathogens of transitional group (TRG), typhus group (TG), and spotted fever group (SFG) rickettsiae differ by clinical manifestations, immunopathology, genome composition, and morphology. We previously showed that lipid A (or endotoxin), the membrane anchor of Gram-negative bacterial lipopolysaccharide (LPS), structurally differs in Rickettsia rickettsii (later-evolving SFG) relative to Rickettsia montanensis (basal SFG), Rickettsia typhi (TG), and Rickettsia akari (TRG). As lipid A structure influences recognition potential in vertebrate LPS sensors, further assessment of Rickettsia lipid A structural heterogeneity is needed. Here, we sidestepped the difficulty of ex vivo lipid A chemical extraction by utilizing fast lipid analysis technique adopted for use with tandem mass spectrometry, a new procedure for generating lipid A structures directly from host cell-purified bacteria. These data confirm that later-evolving SFG pathogens synthesize structurally distinct lipid A. Our findings impact interpreting immune responses to different Rickettsia pathogens and utilizing lipid A adjuvant or anti-inflammatory properties in vaccinology.

The structure of NAD+ consuming protein Acinetobacter baumannii TIR domain shows unique kinetics and conformations

Toll-like and interleukin-1/18 receptor/resistance (TIR) domain-containing proteins function as important signaling and immune regulatory molecules. TIR domain-containing proteins identified in eukaryotic and prokaryotic species also exhibit NAD+ hydrolase activity in select bacteria, plants, and mammalian cells. We report the crystal structure of the Acinetobacter baumannii TIR domain protein (AbTir-TIR) with confirmed NAD+ hydrolysis and map the conformational effects of its interaction with NAD+ using hydrogen-deuterium exchange-mass spectrometry. NAD+ results in mild decreases in deuterium uptake at the dimeric interface. In addition, AbTir-TIR exhibits EX1 kinetics indicative of large cooperative conformational changes, which are slowed down upon substrate binding. Additionally, we have developed label-free imaging using the minimally invasive spectroscopic method 2-photon excitation with fluorescence lifetime imaging, which shows differences in bacteria expressing native and mutant NAD+ hydrolase-inactivated AbTir-TIRE208A protein. Our observations are consistent with substrate-induced conformational changes reported in other TIR model systems with NAD+ hydrolase activity. These studies provide further insight into bacterial TIR protein mechanisms and their varying roles in biology.

Two-photon fluorescence lifetime imaging microscopy of NADH metabolism in HIV-1 infected cells and tissues

Rapid detection of microbial-induced cellular changes during the course of an infection is critical to understanding pathogenesis and immunological homeostasis. In the last two decades, fluorescence imaging has received significant attention for its ability to help characterize microbial induced cellular and tissue changes in in vitro and in vivo settings. However, most of these methods rely on the covalent conjugation of large exogenous probes and detection methods based on intensity-based imaging. Here, we report a quantitative, intrinsic, label-free, and minimally invasive method based on two-photon fluorescence lifetime (FLT) imaging microscopy (2p-FLIM) for imaging 1,4-dihydro-nicotinamide adenine dinucleotide (NADH) metabolism of virally infected cells and tissue sections. To better understand virally induced cellular and tissue changes in metabolism we have used 2p-FLIM to study differences in NADH intensity and fluorescence lifetimes in HIV-1 infected cells and tissues. Differences in NADH fluorescence lifetimes are associated with cellular changes in metabolism and changes in cellular metabolism are associated with HIV-1 infection. NADH is a critical co-enzyme and redox regulator and an essential biomarker in the metabolic processes. Label-free 2p-FLIM application and detection of NADH fluorescence using viral infection systems are in their infancy. In this study, the application of the 2p-FLIM assay and quantitative analyses of HIV-1 infected cells and tissue sections reveal increased fluorescence lifetime and higher enzyme-bound NADH fraction suggesting oxidative phosphorylation (OxPhos) compared to uninfected cells and tissues. 2p-FLIM measurements improve signal to background, fluorescence specificity, provide spatial and temporal resolution of intracellular structures, and thus, are suitable for quantitative studies of cellular functions and tissue morphology. Furthermore, 2p-FLIM allows distinguishing free and bound populations of NADH by their different fluorescence lifetimes within single infected cells. Accordingly, NADH fluorescence measurements of individual single cells should provide necessary insight into the heterogeneity of metabolic activity of infected cells. Implementing 2p-FLIM to viral infection systems measuring NADH fluorescence at the single or subcellular level within a tissue can provide visual evidence, localization, and information in a real-time diagnostic or therapeutic metabolic workflow.

Structural determination of Rickettsia lipid A without chemical extraction confirms shorter acyl chains in later-evolving Spotted Fever Group pathogens

Rickettsiae are Gram-negative obligate intracellular parasites of numerous eukaryotes. Human pathogens of the Transitional Group (TRG), Typhus Group (TG), and Spotted Fever Group (SFG) rickettsiae infect blood-feeding arthropods, have dissimilar clinical manifestations, and possess unique genomic and morphological attributes. Lacking glycolysis, rickettsiae pilfer numerous metabolites from host cytosol to synthesize peptidoglycan and lipopolysaccharide (LPS). For LPS, O-antigen immunogenicity varies between SFG and TG pathogens; however, lipid A proinflammatory potential is unknown. We previously demonstrated that R. akari (TRG), R. typhi (TG), and R. montanensis (SFG) produce lipid A with long 2' secondary acyl chains (C16 or C18) compared to short 2' secondary acyl chains (C12) in R. rickettsii (SFG) lipid A. To further probe this structural heterogeneity and estimate a time point when shorter 2' secondary acyl chains originated, we generated lipid A structures for two additional SFG rickettsiae ( R. rhipicephali and R. parkeri ) utilizing Fast Lipid Analysis Technique adopted for use with tandem mass spectrometry (FLAT n ). FLAT n allowed analysis of lipid A structure directly from host cell-purified bacteria, providing substantial improvement over lipid A chemical extraction. FLAT n -derived structures indicate SFG rickettsiae diverging after R. rhipicephali evolved shorter 2' secondary acyl chains. Bioinformatics analysis of Rickettsia LpxL late acyltransferases revealed discrete active sites and hydrocarbon rulers for long versus short 2' secondary acyl chain addition. While the significance of different lipid A structures for diverse Rickettsia pathogens is unknown, our success using FLAT n will facilitate determining how structural heterogeneity impacts interactions with host lipid A receptors and overall inflammatory potential.

IMPORTANCE

Deforestation, urbanization, and homelessness lead to spikes in Rickettsioses. Vector-borne human pathogens of Transitional Group (TRG), Typhus Group (TG), and Spotted Fever Group (SFG) rickettsiae differ by clinical manifestations, immunopathology, genome composition, and morphology. We previously showed that lipid A (or endotoxin), the membrane anchor of Gram-negative bacterial lipopolysaccharide (LPS), structurally differs in R. rickettsii (later-evolving SFG) relative to R. montanensis (basal SFG), R. typhi (TG), and R. akari (TRG). As lipid A structure influences recognition potential in vertebrate LPS sensors, further assessment of Rickettsia lipid A structural heterogeneity is needed. Here, we sidestepped the difficulty of ex vivo lipid A chemical extraction by utilizing FLAT n , a new procedure for generating lipid A structures directly from host cell-purified bacteria. These data confirm later-evolving SFG pathogens synthesize structurally distinct lipid A. Our findings impact interpreting immune responses to different Rickettsia pathogens and utilizing lipid A adjuvant or anti-inflammatory properties in vaccinology.

Development of an anti-Pseudomonas aeruginosa therapeutic monoclonal antibody WVDC-5244

The rise of antimicrobial-resistant bacterial infections is a crucial health concern in the 21st century. In particular, antibiotic-resistant Pseudomonas aeruginosa causes difficult-to-treat infections associated with high morbidity and mortality. Unfortunately, the number of effective therapeutic interventions against antimicrobial-resistant P. aeruginosa infections continues to decline. Therefore, discovery and development of alternative treatments are necessary. Here, we present pre-clinical efficacy studies on an anti-P. aeruginosa therapeutic monoclonal antibody. Using hybridoma technology, we generated a monoclonal antibody and characterized its binding to P. aeruginosa in vitro using ELISA and fluorescence correlation spectroscopy. We also characterized its function in vitro and in vivo against P. aeruginosa. The anti-P. aeruginosa antibody (WVDC-5244) bound P. aeruginosa clinical strains of various serotypes in vitro, even in the presence of alginate exopolysaccharide. In addition, WVDC-5244 induced opsonophagocytic killing of P. aeruginosa in vitro in J774.1 murine macrophage, and complement-mediated killing. In a mouse model of acute pneumonia, prophylactic administration of WVDC-5244 resulted in an improvement of clinical disease manifestations and reduction of P. aeruginosa burden in the respiratory tract compared to the control groups. This study provides promising pre-clinical efficacy data on a new monoclonal antibody with therapeutic potential for P. aeruginosa infections.

NADase activity found in bacterial TIR proteins may aid in innate immune evasion

Pathogenic microbes have evolved various mechanisms to evade recognition by host immune responses, which can lead to the prevalence of disease and infection. Many strains of pathogenic bacteria contain genes encoding Toll/Interleukin-1 receptor (TIR) domain-containing proteins that function through the inhibition of TLR and myeloid differentiation factor 88 (MyD88) signaling. Previous research has also revealed that prokaryotic TIR domains may regulate bacterial and host metabolic pathways by acting as NAD+ glycohydrolases (NADases). We hypothesize that this NADase activity may contribute to the role of bacterial TIRs as virulence factors. In order to test this hypothesis, we observed the effects of TIR NADase activity on the binding interactions between bacterial TIRs and host MyD88, and on the ability of bacterial TIRs to block NF-kB signaling. For this, we have identified amino acids predicted to play a role in TIR NADase activity and have expressed and purified recombinant bacterial TIR proteins that have incorporated these mutations. We then tested the NADase activity of these mutants in comparison with that of wild-type TIR proteins and TIRs with a mutation known to inhibit NADase activity. We are now using TIRs with deficiencies in NADase activity in pull-down assays to test their binding to MyD88 and utilizing RT-PCR to analyze the effects of these mutant TIRs on innate cell activation. This information will allow us to gain a deeper understanding into the relationship between NADase activity in bacterial TIRs and their virulence activity and can potentially uncover new mechanisms for pathogenic evasion of host immune defenses.

Supported by grant from NIH (R25 GM119970 04)

Structure of NAD+ consuming Acinetobacter baumannii TIR domain

Toll-like and Interleukin-1/18 receptor (TIR) resistance proteins have been identified across biology to function as important multimodal signal transduction and immune regulatory molecules. Select TIR domain containing proteins identified in both eukaryotic and prokaryotic species have also been found to have NAD+ hydrolase activity in bacteria, plants and in mammalian cells. We report the crystal structure of the Acinetobacter baumannii Toll-Interleukin-1 receptor resistance domain protein (AbTIR) determined to a resolution of 2.8 Å, confirm its enzymatic function in NAD+ hydrolysis and map its interaction with NAD+ using HDX-MS. Additionally, we have developed a novel assay for measuring AbTIR’s enzymatic activity in live bacteria using label-free quantitative two-photon fluorescence lifetime (FLT) imaging microscopy (2p-FLIM). These studies provide new insight into TIR protein mechanisms and their varying roles across biology.

Supported by R01 AI-082299, R21 CA191726-01 

Molecular Basis of Selective Cytokine Signaling Inhibition by Antibodies Targeting a Shared Receptor

Interleukin-1 (IL-1) family cytokines are potent mediators of inflammation, acting to coordinate local and systemic immune responses to a wide range of stimuli. Aberrant signaling by IL-1 family cytokine members, however, is linked to myriad inflammatory syndromes, autoimmune conditions and cancers. As such, blocking the inflammatory signals inherent to IL-1 family signaling is an established and expanding therapeutic strategy. While several FDA-approved IL-1 inhibitors exist, including an Fc fusion protein, a neutralizing antibody, and an antagonist cytokine, none specifically targets the co-receptor IL-1 receptor accessory protein (IL-1RAcP). Most IL-1 family cytokines form productive signaling complexes by binding first to their cognate receptors – IL-1RI for IL-1α and IL-1β; ST2 for IL-33; and IL-36R for IL-36α, IL-36β and IL-36γ – after which they recruit the shared secondary receptor IL-1RAcP to form a ternary cytokine/receptor/co-receptor complex. Recently, IL-1RAcP was identified as a biomarker for both AML and CML. IL-1RAcP has also been implicated in tumor progression in solid tumors and an anti-IL1RAP antibody (nadunolimab, CAN04) is in phase II clinical studies in pancreatic cancer and non-small cell lung cancer (NCT03267316). As IL-1RAcP is common to all of the abovementioned IL-1 family cytokines, targeting this co-receptor raises the possibility of selective signaling inhibition for different IL-1 family cytokines. Indeed, previous studies of IL-1β and IL-33 signaling complexes have revealed that these cytokines employ distinct mechanisms of IL-1RAcP recruitment even though their overall cytokine/receptor/co-receptor complexes are structurally similar. Here, using functional, biophysical, and structural analyses, we show that antibodies specific for IL-1RAcP can differentially block signaling by IL-1 family cytokines depending on the distinct IL-1RAcP epitopes that they engage. Our results indicate that targeting a shared cytokine receptor is a viable therapeutic strategy for selective cytokine signaling inhibition.

Adaptation of a CURE course aimed at characterization of host-pathogen interactions for on-line learning

Course-based undergraduate research experiences (CUREs) aim to engage a large, diverse group of students in authentic research, promote student research skills, content knowledge, scientific literacy, critical thinking and analysis skills, support student self-efficacy, and at the same time provide a means to advance faculty research productivity. Addressing each of these varied goals of a CURE course is a challenge, and became even more challenging when classes were forced on-line for the COVID-19 pandemic. In Fall of 2020, we adapted our CURE course, which seeks to engage students at Towson University with research ongoing at the University of Maryland, School of Medicine, for virtual learning. To move the course on-line, we focused on activities that could easily be adapted to a virtual environment, such as those focusing on bioinformatics analysis, research design, data analysis, scientific writing and on-line lab simulations. Students were tasked with becoming ‘project managers’—designing hypotheses and protocols and choosing experimental variables and controls, while instructors and an undergraduate learning assistant carried out the experiments, videotaping so students could become familiar with the techniques. While the drawbacks of the virtual CURE course were many, including the lack of student involvement in hands-on bench work, benefits of the virtual CURE included more time and attention devoted to critical skills such as research design, data analysis and scientific writing. Future designs of CURE courses may benefit from increased attention to these skills, even upon return to in-person learning.

Contribution of the NADase function of bacterial TIR domain proteins to the inhibition of innate immune responses

Pathogenic microbes have evolved various mechanisms to evade recognition by host immune responses, which can lead to the prevalence of disease and infection. Many strains of pathogenic bacteria contain genes encoding Toll/Interleukin-1 receptor (TIR) domain-containing proteins that function through the inhibition of TLR and myeloid differentiation factor 88 (MyD88) signaling. Previous research has also revealed that prokaryotic TIR domains may regulate bacterial and host metabolic pathways by acting as NAD+ glycohydrolases (NADases). We hypothesize that this NADase activity may contribute to the role of bacterial TIRs as virulence factors. In order to test this hypothesis, we observed the effects of TIR NADase activity on the binding interactions between bacterial TIRs and host MyD88, and on the ability of bacterial TIRs to block NF-kB signaling. For this, we have identified amino acids predicted to play a role in TIR NADase activity and have expressed and purified recombinant bacterial TIR proteins that have incorporated these mutations. We then tested the NADase activity of these mutants in comparison with that of wild-type TIR proteins and TIRs with mutations already known to inhibit NADase activity. We are now using mutant TIRs with deficiencies in NADase activity in pull-down assays to test their binding to MyD88 and utilizing reporter assays to analyze the effects of these mutant TIRs on NF-kB signaling. This information will allow us to gain a deeper understanding into the relationship between NADase activity in bacterial TIRs and their virulence activity, and can potentially uncover new mechanisms for pathogenic evasion of host immune defenses.

Lipid A mimetics BECC438 and BECC470 potentiate durable and balanced immune responses using an ovalbumin murine vaccine model

The need for effective infectious disease vaccines has become an inescapable topic over the past year. Continued development of next-generation vaccines that provide robust protective immunity is imperative. Such vaccines will likely include an adjuvant that avoids excessive adverse reactions and allows for dose and antigen sparing. Bacterial lipid A mimetics BECC438 and BECC470 have recently emerged as lead adjuvant candidates across several experimental models of infectious disease including Yersinia pestis (plague), human papilloma virus (HPV), and influenza-A (flu). To further define BECC438 and BECC470 as immuno-adjuvants, even without antigen from an infectious pathogen, studies presented here use ovalbumin (Ova) as a model antigen in a murine prime-boost vaccine model. Higher magnitude and more balanced production of antibody isotypes IgG1 and IgG2 are observed when BECC adjuvants are compared to classic adjuvants alum and PHAD. This optimal antibody response is durable and maintained for at least 12 weeks post-vaccination. Initial experiments use C57BL6 mice and are expanded to include BALBc and CD-1 (outbred) mice. Observed immune metrics maintained similar trends across male and females, and genetic backgrounds tested. Biacore immunogenicity analysis of C57BL6 serum found an increased half-life of Ova-specific antibodies in BECC438-adjuvanted animals potentially indicative of a higher antigen binding affinity. Toxicity studies conducted in New Zealand White rabbits report that BECC438 was well tolerated with no significant reactogenicity after 50μg and 100μg intra-muscular adjuvant injection. These studies provide continued evidence supporting development of BECC adjuvants in vaccines for human use.

Structure and dynamics of an α-fucosidase reveal a mechanism for highly efficient IgG transfucosylation

Fucosylation is important for the function of many proteins with biotechnical and medical applications. Alpha-fucosidases comprise a large enzyme family that recognizes fucosylated substrates with diverse α-linkages on these proteins. Lactobacillus casei produces an α-fucosidase, called AlfC, with specificity towards α(1,6)-fucose, the only linkage found in human N-glycan core fucosylation. AlfC and certain point mutants thereof have been used to add and remove fucose from monoclonal antibody N-glycans, with significant impacts on their effector functions. Despite the potential uses for AlfC, little is known about its mechanism. Here, we present crystal structures of AlfC, combined with mutational and kinetic analyses, hydrogen–deuterium exchange mass spectrometry, molecular dynamic simulations, and transfucosylation experiments to define the molecular mechanisms of the activities of AlfC and its transfucosidase mutants. Our results indicate that AlfC creates an aromatic subsite adjacent to the active site that specifically accommodates GlcNAc in α(1,6)-linkages, suggest that enzymatic activity is controlled by distinct open and closed conformations of an active-site loop, with certain mutations shifting the equilibrium towards open conformations to promote transfucosylation over hydrolysis, and provide a potentially generalizable framework for the rational creation of AlfC transfucosidase mutants.

AlfC transfucosidase is used to modulate fucosylation of glycans decorating monoclonal antibodies. Herein, structural and biophysical characterization reveals the enzymatic mechanism of AlfC and a blueprint for the design of AlfC mutants with novel specificities and functions.

Emerging of a SARS-CoV-2 viral strain with a deletion in nsp1

BACKGROUND

The new Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), which was first detected in Wuhan (China) in December of 2019 is responsible for the current global pandemic. Phylogenetic analysis revealed that it is similar to other betacoronaviruses, such as SARS-CoV and Middle-Eastern Respiratory Syndrome, MERS-CoV. Its genome is ∼ 30 kb in length and contains two large overlapping polyproteins, ORF1a and ORF1ab that encode for several structural and non-structural proteins. The non-structural protein 1 (nsp1) is arguably the most important pathogenic determinant, and previous studies on SARS-CoV indicate that it is both involved in viral replication and hampering the innate immune system response. Detailed experiments of site-specific mutagenesis and in vitro reconstitution studies determined that the mechanisms of action are mediated by (a) the presence of specific amino acid residues of nsp1 and (b) the interaction between the protein and the host's small ribosomal unit. In fact, substitution of certain amino acids resulted in reduction of its negative effects.

METHODS

A total of 17,928 genome sequences were obtained from the GISAID database (December 2019 to July 2020) from patients infected by SARS-CoV-2 from different areas around the world. Genomes alignment was performed using MAFFT (REFF) and the nsp1 genomic regions were identified using BioEdit and verified using BLAST. Nsp1 protein of SARS-CoV-2 with and without deletion have been subsequently modelled using I-TASSER.

RESULTS

We identified SARS-CoV-2 genome sequences, from several Countries, carrying a previously unknown deletion of 9 nucleotides in position 686-694, corresponding to the AA position 241-243 (KSF). This deletion was found in different geographical areas. Structural prediction modelling suggests an effect on the C-terminal tail structure.

CONCLUSIONS

Modelling analysis of a newly identified deletion of 3 amino acids (KSF) of SARS-CoV-2 nsp1 suggests that this deletion could affect the structure of the C-terminal region of the protein, important for regulation of viral replication and negative effect on host's gene expression. In addition, substitution of the two amino acids (KS) from nsp1 of SARS-CoV was previously reported to revert loss of interferon-alpha expression. The deletion that we describe indicates that SARS-CoV-2 is undergoing profound genomic changes. It is important to: (i) confirm the spreading of this particular viral strain, and potentially of strains with other deletions in the nsp1 protein, both in the population of asymptomatic and pauci-symptomatic subjects, and (ii) correlate these changes in nsp1 with potential decreased viral pathogenicity.

Therapeutic targeting of intracellular Toll-like and interleukin-1/18 receptor (TIR) resistance domain containing proteins for protection against infection, inflammation and disease

TIR domain containing proteins are important immune associated proteins shared among Toll-like and interleukin-1/18 receptor family members. In a recent discovery select bacterial, plant and human TIR proteins exhibit enzymatic activity in binding and processing nicotinamide adenine dinucleotide (NAD+). Based on their abilities to facilitate signaling across biology, we hypothesize that TIR proteins represent unique therapeutic targets for modulating infection, inflammation and disease. Our previous structural studies of bacterial-host TIR proteins B. melitensis (TcpB) and uropathogenic E. coli CFT073 (TcpC) with human host TIRAP and MyD88 characterized peptides that negatively regulate signaling and infection. From these studies we identified interactions that are at or near reported biological TIR protein interfaces. In particular, we identified a functionally important motif found conserved on the C helix of most bacterial, human host and NAD+ consuming TIR proteins. As proof of concept for select targeting of TIR proteins and this region in particular we have used the TLR4 antagonist, TAK-242, which selectively binds within this motif. Treatment with TAK-242 or TLR4-C747S blocks LPS signaling. Additionally, TAK-242 protected mice from lethal influenza challenge similar to an extracellular TLR4 antagonist, Eritoran. Bioinformatic analysis of the region targeted by TAK242 show that it is located within the WxxxE structural motif identified to be important for protecting against microtubule destabilization and includes a catalytically essential glutamic acid (E) residue conserved among nearly all NAD+ consuming TIR proteins. These studies provide a framework for future studies targeting TIR protein function.

Development of a CURE course aimed at characterization of bacterial Toll/interleukin 1 receptor (TIR) domain-containing proteins

Course-based undergraduate research experiences (CUREs) can engage a large, diverse group of students in authentic research, promote student research skills, student content knowledge, scientific literacy, critical thinking and analysis skills, support student self-efficacy, and at the same time provide a means to advance faculty research productivity. These varied goals of a CURE course, at times, can prove to be competing. For example, courses aimed at providing advanced levels of student input in design of research questions, hypotheses and protocols can veer from faculty research goals. In an effort to balance these competing objectives, we designed a CURE course engaging students at Towson University with research ongoing at the University of Maryland, School of Medicine aimed at characterizing the function of bacterial Toll/interleukin 1 receptor (TIR) domain containing proteins. Bacterial TIR proteins were originally characterized as virulence factors that impede mammalian innate immune signaling, but recently also have been shown to exhibit enzymatic NADase activity. Students in the CURE course used bioinformatics analysis of modeled structures of bacterial TIRs to predict sites for NADase function and hypothesized the effects of mutations of these sites on TIR functions. Students then designed and created recombinantly-expressed proteins mutated at their predicted sites and tested their mutant proteins for both NADase function and potential inhibition of mammalian innate immune signaling. This course outline thus allowed student engagement in project design and hypothesis formation, while also maintaining projects aimed at advancing a specific faculty research program.

Select targeting of intracellular Toll-interleukin-1 receptor resistance domains for protection against influenza-induced disease

TLRs are a family of PRRs that respond to PAMPs or host-derived Danger-Associated Molecular Patterns (DAMPs) to initiate host inflammation and immune responses. TLR dimerization and recruitment of adapter molecules is critical for intracellular signaling and is mediated through intracellular Toll-Interleukin 1 Receptor Resistance (TIR) domain interactions. Human TIR domains, including reported structures of TIR1, TIR2, TIR6, TIR10, TIRAP, and MyD88, contain Cysteine (Cys) interactions or modifications that are disproportionally at, or near, reported biological TIR interfaces, or in close proximity to functionally important regions. Therefore, we hypothesized that intracellular TIR Cys regulation may have greater functional importance than previously appreciated. Expression of mutant TLR4-C747S or treatment of TLR4 reporter cells with a small molecule, Cys-binding inhibitor of TLR4, TAK-242, abrogated LPS signaling in vitro . Using TAK-242, mice were protected from lethal influenza challenge as previously reported for extracellular TLR4 antagonists. Molecular modeling and sequence analysis of the region surrounding TLR4-Cys747 indicate conservation of a WxxxE motif identified among bacterial and NAD+-consuming TIRs, as well as within the TIRs domains of surface TLRs 1, 2, 4, 6, and 10. Together, these data support the hypothesis that critical Cys within the TIR domain are essential for TLR4 functionality.

MyD88 dimerization inhibitors for targeting Diffuse Large B-cell Lymphomas

A recurring single amino acid somatic mutation associated with human diffuse large B cell lymphomas (DLBCLs), correlates with tumor cell proliferation and survival involving spontaneous and sustained activation of MyD88-dependent NF-κB and Janus Kinase (JAK) signaling pathways. MyD88 acts as a central signaling adapter for mediating innate and cytokine driven inflammation for the Interleukin-1 (IL-1R) and Toll-like receptors (TLRs). Computer aided molecular modeling of MyD88 and in silico screening have identified and functionally characterized MyD88 specific small molecule compounds shown to protect against Staphylococcal enterotoxin B (SEB) induced death in animal models. We hypothesize that MyD88 specific small molecule compounds may also be useful in treating DLBCLs bearing the oncogenic mutation MYD88L265P. Using in vitro and in vivo studies we evaluate MyD88 specific small molecule compounds for the ability to inhibit tumor cell proliferation and signaling in human patient cancer cells OCI Ly3 bearing the oncogenic mutation MYD88 L265P and OCI Ly19 DLBCLs. Previously we identified differences in the ability of MyD88 small molecule compounds to inhibit cell proliferation in activated human B cell lymphoma cells bearing the MyD88 L265P mutation. We now correlate these differences with a reduction of MyD88 interaction with IRAK in small molecule treated OCI-Ly3 cells bearing the MYD88 L265P mutation in comparison to OCI-Ly19 (wt-MyD88) and treated controls, as measured by CoIP. We continue to characterize MyD88 specific small molecule compounds that target MyD88 dimerization for their ability to reduce MyD88 containing signaling complexes in DLBCLs bearing MYD88 L265P mutation.

Targeting of Diffuse Large B-cell Lymphomas using MyD88 small molecule inhibitors

A mutation associated with nearly 1/3 of human diffuse large B cell lymphomas (DLBCLs) has been identified within MyD88. This mutation correlates with tumor cell proliferation and survival involving spontaneous and sustained activation of NF-κB signaling. MyD88 is a central signaling adapter for the Interleukin-1 (IL-1R) and Toll-like receptors (TLRs). In normal healthy cells, MyD88 is thought to be held in an auto-inhibitory state with its own death and TIR domains fused together in negative self-regulation until activated by appropriate receptor mediated ligand engagement.

Observation

CADD derived small molecule compounds inhibit MyD88 dimer formation and protect against Staphylococcal enterotoxin B (SEB) induced death in animal models.

Hypothesis

Based on this observation we hypothesize that MyD88 specific small molecule inhibitors may be useful in treating DLBCLs bearing MyD88L265P.

Approach

Using in vitro and in vivo studies we characterize MyD88 specific SMIs for the ability to inhibit tumor cell proliferation and signaling in cancer cells bearing the oncogenic mutation MyD88L265P.

Results

1) MyD88 SMIs are able to inhibit cell proliferation of DLBCLs bearing the MyD88L265P as measured by MTS cell proliferation assay, 2) recombinant MyD88 and SMIs exhibit unique binding chromatograms in comparison to DMSO controls as measured by thermal shift assay and 3) MyD88 SMIs are partially able to inhibit LPS activated TLR4 cell NF-kB signaling in comparison to the TLR4 specific inhibitor TAK242. Future studies defining the molecular mechanism of this mutation with additional human patient tumor isolates will inform and propel development of novel therapeutics to counteract both inflammation as well as tumor formation.

Select targeting of intracellular Cysteine in Toll-Interleukin-1 receptor resistance domains for protection against Influenza

Regulation of Toll-like receptor (TLR) signaling using small molecule agonists and antagonists is widely sought after for controlling inflammation and disease. Recently, small molecule and TIR-based-decoy-peptide inhibitors targeting intracellular Toll-Interleukin-1 receptor (TIR) resistance domains have been identified and functionally characterized to protect against lethality in animal models of infection, inflammation and disease. We observe multiple instances of targeting, modification or involvement of conserved Cysteine residues within intracellular TIR domains by functionally characterized small molecule and decoy peptide inhibitors. We hypothesize that cysteine interactions among intracellular Toll and Interleukin-1 receptors may possess therapeutic value. We have used molecular modeling, X-ray crystallography and in vitro and in vivo functional characterization to characterize TIR cysteine interactions in molecular detail using previously functionally verified derived small molecule and decoy-peptide inhibitors. As a proof of concept, we have used the small molecule receptor antagonist TAK242, which selectively binds Cys747 located in the intracellular TIR domain of TLR4. We show that intracellular targeting of TLR4 TIR domain cysteine using TAK242 is able block LPS activated TLR4 NF-kB signaling in cells and protects mice against lethal influenza (PR8) infection at a lower dose than the ectodomain TLR4 antagonist Eritoran. Structural analysis shows this Cysteine residue to be highly conserved among other surface receptor TLRs 1,2,4,5,6 and 10. Additionally, surface plasmon resonance binding of cysteine containing TIR-decoy peptides, is sensitive to reduction using 2-Mercaptoethanol.

Innate immune signaling inhibition via disruption of adapter interactions

Toll-like receptors (TLR) form homo- or heterodimers in response to pathogen-associated molecular patterns. The TLR homo- or heterodimers establish an intracellular signaling platform that recruits the signaling adapter protein Toll-Interleukin 1 Receptor (TIR) domain containing adaptor protein (TIRAP). This receptor-mediated platform initiates a signaling cascade which leads to NF-kB activation, cytokine production, and inflammation. Inflammation leads to pathogen clearance; however, excessive stimulation of the innate immune pathway can lead to injury and death. We are investigating mechanisms to disrupt TIRAP-mediated TLR signaling via two mechanisms: the bacterial TIR domain protein, TcpB from Brucella sp., and the decoy peptide, 2R9. We have previously determined the structures of TIRAP and TcpB. Presumably via molecular interactions with TIRAP, TcpB inhibited NF-kB activation. We now report surface plasma resonance binding of TIRAP with TcpB. The decoy peptide, 2R9, was derived from the TLR2 TIR domain D-helix. We have previously described interactions between 2R9 and TIRAP via surface plasma resonance. Based on the ability of 2R9 peptide to protect against lethality in response to acute influenza infection, 2R9 peptide could highlight a novel drug target to prevent injury and death caused by innate immune over activation. Using recombinant TIRAP with TcpB and 2R9 peptide, we are performing structural studies to characterize molecular interactions to identify putative sites for therapeutic intervention.

Molecular interactions of small molecule inhibitors targeting cytoplasmic TIR domains

Regulation of Toll-like receptor (TLR) signaling using small molecule agonists and antagonists have been widely sought after for controlling inflmation and disease. Most studies have focused on therapeutic targeting of TLR extracellular ligand binding domains. Recently, Computer-aided drug design (CADD) screens specifically targeting intracellular Toll-Interleukin-1 receptor resistance domains have identified and functionally characterized several small molecule and peptide inhibitors which protect against lethality in animal models of infection, inflammation and disease. We have sought to structurally characterize the molecular interactions of CADD derived small molecule inhibitors with respective TLR-TIR domains by determining the X-ray co-crystal structures of TLR2 –TIR domain in the presence of C29 and its substructure O-vanillin. Positive electron density is observed near the BB loop and residue Ile 685 of native TLR2-TIR in the presence of the small molecule inhibitor (C29) exhibit compared with the native apo form of this structure. However, the presence of (S-(DIMETHYLARSENIC) CYSTEINE) in this crystallization condition complicate analysis. To rule out the effects of DMSO and (S-(DIMETHYLARSENIC) CYSTEINE) we sought to examine small molecule inhibitor C29L substructure (o-Vanillin) in a second crystal form of TLR2 and which contains a more simplified crystallization condition grown in the presence of 1mM of C29L. This co-crystal exhibits positive electron density located in an around the BB loop compared with apo forms of this structure. Additionally, in this recent structure form we observe additional DD loop density previously not defined in the originally reported crystal form.

Molecular interactions in interleukin and toll-like receptor signaling pathways

The ability of a single protein fold to make multi-modal interactions with itself and others for transmitting biological signals across multiple receptor families is a recurring theme in signal transduction. The Toll/IL-1 receptor (TIR) domain represents an evolutionarily conserved alpha-beta Flavodoxin-like protein fold, which has evolved complex multifaceted molecular interactions capable of transmitting a variety of developmental and immunological signals. In mammals, TIR domains are found on both interleukin-1 receptors (IL-1Rs) and Toll-like receptors (TLRs), as well as in cytoplasmic signaling adaptors and endogenous regulatory proteins. Appropriate TIR-TIR mediated immune interactions result in cytokine responses, pathogen clearance and host immune protection, while inappropriate signaling can lead to autoimmunity, inflammation and death. In the past decade, a number of three-dimensional structures of individual TIR domains have been elucidated. When coupled with the wealth of information from mutagenesis, genetic and peptide studies, this structural data provides additional insight to the molecular mechanisms underlying signal transduction mediated by interactions between TIR domains. Owing to their ability to regulate both innate and adaptive immune responses in a variety of organisms including humans, TIR domain-mediated molecular interactions are of intense interest for therapies targeting autoimmunity, cancer and emerging host-pathogen interactions. Here, we review progress in the development of peptides, peptidomimetics and small molecules designed to regulate TIR-dependent signaling in the context of recent advances in structural and molecular studies of TIR domain proteins and their interactions.

Cardiac troponin I Pro82Ser variant induces diastolic dysfunction, blunts β-adrenergic response, and impairs myofilament cooperativity

Troponin I (TnI) variant Pro82Ser (cTnIP82S) was initially considered a disease-causing mutation; however, later studies suggested the contrary. We tested the hypothesis of whether a causal link exists between cTnIP82S and cardiac structural and functional remodeling, such as during aging or chronic pressure overload. A cardiac-specific transgenic (Tg) mouse model of cTnIP82S was created to test this hypothesis. During aging, Tg cTnIP82S displayed diastolic dysfunction, characterized by longer isovolumetric relaxation time, and impaired ejection and relaxation time. In young, Tg mice in vivo pressure-volume loops and intact trabecular preparations revealed normal cardiac contractility at baseline. However, upon β-adrenergic stimulation, a blunted contractile reserve and no hastening in left ventricle relaxation were evident in vivo, whereas, in isolated muscles, Ca(2+) transient amplitude isoproterenol dose-response was blunted. In addition, when exposed to chronic pressure overload, Tg mice show exacerbated hypertrophy and decreased contractility compared with age-matched non-Tg littermates. At the molecular level, this mutation significantly impairs myofilament cooperative activation. Importantly, this occurs in the absence of alterations in TnI or myosin-binding protein C phosphorylation. The cTnIP82S variant occurs near a region of interactions with troponin T; therefore, structural changes in this region could explain its meaningful effects on myofilament cooperativity. Our data indicate that cTnIP82S mutation modifies age-dependent diastolic dysfunction and impairs overall contractility after β-adrenergic stimulation or chronic pressure overload. Thus cTnIP82S variant should be regarded as a disease-modifying factor for dysfunction and adverse remodeling with aging and chronic pressure overload.

Structure of Clostridium difficile PilJ exhibits unprecedented divergence from known type IV pilins

Type IV pili are produced by many pathogenic Gram-negative bacteria and are important for processes as diverse as twitching motility, cellular adhesion, and colonization. Recently, there has been an increased appreciation of the ability of Gram-positive species, including Clostridium difficile, to produce Type IV pili. Here we report the first three-dimensional structure of a Gram-positive Type IV pilin, PilJ, demonstrate its incorporation into Type IV pili, and offer insights into how the Type IV pili of C. difficile may assemble and function. PilJ has several unique structural features, including a dual-pilin fold and the incorporation of a structural zinc ion. We show that PilJ is incorporated into Type IV pili in C. difficile and present a model in which the incorporation of PilJ into pili exposes the C-terminal domain of PilJ to create a novel interaction surface.

Crystal structures of the Toll/Interleukin-1 receptor (TIR) domains from the Brucella protein TcpB and host adaptor TIRAP reveal mechanisms of molecular mimicry

The Toll/IL-1 receptor (TIR) domains are crucial innate immune signaling modules. Microbial TIR domain-containing proteins inhibit Toll-like receptor (TLR) signaling through molecular mimicry. The TIR domain-containing protein TcpB from Brucella inhibits TLR signaling through interaction with host adaptor proteins TIRAP/Mal and MyD88. To characterize the microbial mimicry of host proteins, we have determined the X-ray crystal structures of the TIR domains from the Brucella protein TcpB and the host adaptor protein TIRAP. We have further characterized homotypic interactions of TcpB using hydrogen/deuterium exchange mass spectrometry and heterotypic TcpB and TIRAP interaction by co-immunoprecipitation and NF-κB reporter assays. The crystal structure of the TcpB TIR domain reveals the microtubule-binding site encompassing the BB loop as well as a symmetrical dimer mediated by the DD and EE loops. This dimerization interface is validated by peptide mapping through hydrogen/deuterium exchange mass spectrometry. The human TIRAP TIR domain crystal structure reveals a unique N-terminal TIR domain fold containing a disulfide bond formed by Cys(89) and Cys(134). A comparison between the TcpB and TIRAP crystal structures reveals substantial conformational differences in the region that encompasses the BB loop. These findings underscore the similarities and differences in the molecular features found in the microbial and host TIR domains, which suggests mechanisms of bacterial mimicry of host signaling adaptor proteins, such as TIRAP.

R753Q polymorphism inhibits Toll-like receptor (TLR) 2 tyrosine phosphorylation, dimerization with TLR6, and recruitment of myeloid differentiation primary response protein 88

The R753Q polymorphism in the Toll-IL-1 receptor domain of Toll-like receptor 2 (TLR2) has been linked to increased incidence of tuberculosis and other infectious diseases, but the mechanisms by which it affects TLR2 functions are unclear. Here, we studied the impact of the R753Q polymorphism on TLR2 expression, hetero-dimerization with TLR6, tyrosine phosphorylation, and recruitment of myeloid differentiation primary response protein (MyD) 88 and MyD88 adapter-like (Mal). Complementation of HEK293 cells with transfected WT or R753Q TLR2 revealed their comparable total levels and only minimal changes in cell surface expression of the mutant species. Notably, even a 100-fold increase in amounts of transfected R753Q TLR2 versus WT variant did not overcome the compromised ability of the mutant TLR2 to activate nuclear factor κB (NF-κB), indicating that a minimal decrease in cell surface levels of the R753Q TLR2 cannot account for the signaling deficiency. Molecular modeling studies suggested that the R753Q mutation changes the electrostatic potential of the DD loop and results in a discrete movement of the residues critical for protein-protein interactions. Confirming these predictions, biochemical assays demonstrated that R753Q TLR2 exhibits deficient agonist-induced tyrosine phosphorylation, hetero-dimerization with TLR6, and recruitment of Mal and MyD88. These proximal signaling deficiencies correlated with impaired capacities of the R753Q TLR2 to mediate p38 phosphorylation, NF-κB activation, and induction of IL-8 mRNA in transfected HEK293 cells challenged with inactivated Mycobacterium tuberculosis or mycobacterial components. Thus, the R753Q polymorphism renders TLR2 signaling-incompetent by impairing its tyrosine phosphorylation, dimerization with TLR6, and recruitment of Mal and MyD88.

Characterization of DC-SIGN/R interaction with human immunodeficiency virus type 1 gp120 and ICAM molecules favors the receptor's role as an antigen-capturing rather than an adhesion receptor

The dendritic cell (DC)-specific intercellular adhesion molecule 3 (ICAM-3)-grabbing nonintegrin binding receptor (DC-SIGN) was shown to bind human immunodeficiency virus type 1 (HIV-1) viral envelope protein gp120 and proposed to function as a Trojan horse to enhance trans-virus infection to host T cells. To better understand the mechanism by which DC-SIGN and DC-SIGNR selectively bind HIV-1 gp120, we constructed a series of deletion mutations in the repeat regions of both receptors. Different truncated receptors exist in different oligomeric forms. The carbohydrate binding domain without any repeats was monomeric, whereas the full extracellular receptors existed as tetramers. All reconstituted receptors retained their ability to bind gp120. The dissociation constant, however, differed drastically from micromolar values for the monomeric receptors to nanomolar values for the tetrameric receptors, suggesting that the repeat region of these receptors contributes to the avidity of gp120 binding. Such oligomerization may provide a mechanism for the receptor to selectively recognize pathogens containing multiple high-mannose-concentration carbohydrates. In contrast, the receptors bound to ICAMs with submicromolar affinities that are similar to those of two nonspecific cell surface glycoproteins, FcgammaRIIb and FcgammaRIII, and the oligomerization of DC-SIGNR resulted in no increase in binding affinity to ICAM-3. These findings suggest that DC-SIGN may not discriminate other cell surface glycoproteins from ICAM-3 binding. The pH dependence in DC-SIGN binding to gp120 showed that the receptor retained high-affinity gp120 binding at neutral pH but lost gp120 binding at pH 5, suggesting a release mechanism of HIV in the acidic endosomal compartment by DC-SIGN. Our work contradicts the function of DC-SIGN as a Trojan horse to facilitate HIV-1 infection; rather, it supports the function of DC-SIGN/R (a designation referring to both DC-SIGN and DC-SIGNR) as an antigen-capturing receptor.

The structure of DC-SIGNR with a portion of its repeat domain lends insights to modeling of the receptor tetramer

The dendritic cell-specific ICAM-3 non-integrin (DC-SIGN) and its close relative DC-SIGNR recognize various glycoproteins, both pathogenic and cellular, through the receptor lectin domain-mediated carbohydrate recognition. While the carbohydrate-recognition domains (CRD) exist as monomers and bind individual carbohydrates with low affinity and are permissive in nature, the full-length receptors form tetramers through their repeat domain and recognize specific ligands with high affinity. To understand the tetramer-based ligand binding avidity, we determined the crystal structure of DC-SIGNR with its last repeat region. Compared to the carbohydrate-bound CRD structure, the structure revealed conformational changes in the calcium and carbohydrate coordination loops of CRD, an additional disulfide bond between the N and the C termini of the CRD, and a helical conformation for the last repeat. On the basis of the current crystal structure and other published structures with sequence homology to the repeat domain, we generated a tetramer model for DC-SIGN/R using homology modeling and propose a ligand-recognition index to identify potential receptor ligands.

Oxygen isotopes and the moon-forming giant impact

We have determined the abundances of 16O, 17O, and 18O in 31 lunar samples from Apollo missions 11, 12, 15, 16, and 17 using a high-precision laser fluorination technique. All oxygen isotope compositions plot within +/-0.016 per mil (2 standard deviations) on a single mass-dependent fractionation line that is identical to the terrestrial fractionation line within uncertainties. This observation is consistent with the Giant Impact model, provided that the proto-Earth and the smaller impactor planet (named Theia) formed from an identical mix of components. The similarity between the proto-Earth and Theia is consistent with formation at about the same heliocentric distance. The three oxygen isotopes (delta17O) provide no evidence that isotopic heterogeneity on the Moon was created by lunar impacts.

Crystal structure of the HLA-Cw3 allotype-specific killer cell inhibitory receptor KIR2DL2

Killer cell inhibitory receptors (KIR) protect class I HLAs expressing target cells from natural killer (NK) cell-mediated lysis. To understand the molecular basis of this receptor-ligand recognition, we have crystallized the extracellular ligand-binding domains of KIR2DL2, a member of the Ig superfamily receptors that recognize HLA-Cw1, 3, 7, and 8 allotypes. The structure was determined in two different crystal forms, an orthorhombic P212121 and a trigonal P3221 space group, to resolutions of 3.0 and 2.9 A, respectively. The overall fold of this structure, like KIR2DL1, exhibits K-type Ig topology with cis-proline residues in both domains that define beta-strand switching, which sets KIR apart from the C2-type hematopoietic growth hormone receptor fold. The hinge angle of KIR2DL2 is approximately 80 degrees, 14 degrees larger than that observed in KIR2DL1 despite the existence of conserved hydrophobic residues near the hinge region. There is also a 5 degrees difference in the observed hinge angles in two crystal forms of 2DL2, suggesting that the interdomain hinge angle is not fixed. The putative ligand-binding site is formed by residues from several variable loops with charge distribution apparently complementary to that of HLA-C. The packing of the receptors in the orthorhombic crystal form offers an intriguing model for receptor aggregation on the cell surface.

Pennsylvania dental hygienists' knowledge, attitudes, and infection control practices in relation to AIDS and AIDS patients

PURPOSE

Limited documentation is found on dental hygienists' attitudes toward acquired immunodeficiency syndrome (AIDS) patients and their knowledge and practice of clinical infection control to prevent disease transmission to themselves and their patients. The purpose of this paper was to survey practicing Pennsylvania dental hygienists to document 1) their infection control practices; 2) their attitudes towards AIDS patients; and 3) their knowledge of clinical infection control practices.

METHODS

A self-administered survey questionnaire, with fixed-alternative responses, was mailed in January 1991 to a random sample (N = 300) of licensed, practicing Pennsylvania dental hygienists. The questionnaire comprised eight multiple-choice questions for demographic purposes and 89 Likert-type questions eliciting information in five areas: AIDS-related knowledge, attitudes toward AIDS patients, knowledge of recommended Centers for Disease Control and Prevention (CDC) infection control measures, individual infection control measures, and individual laboratory infection control measures. Means and modes for individual questions and for specific categories were determined and analyzed utilizing Spearman rho correlation coefficients (p < .05). Mean scores were also tabulated for actual operator/laboratory infection control practices for both a routine patient and an AIDS patient. Those scores were analyzed utilizing the Wilcoxen signed-ranks test.

RESULTS

Two hundred twenty questionnaires were returned for a 73.3% initial response rate. One hundred fifty-four of those returned were usable, for a 64% response rate. Results indicated that 94.2% of surveyed dental hygienists had comprehensive knowledge about AIDS and 92% had comprehensive knowledge of CDC-recommended infection control procedures. Eighty-five percent of respondents possessed a moderate or high feeling of worry concerning treatment of AIDS patients. The majority of surveyed dental hygienists routinely practiced the use of glasses, masks, and gloves; the use of disposable items; and surface disinfection of light handles, instrument bracket trays, and patient chair switches. Knowledge of recommended infection control procedures for dentistry was found to be associated (r = .22) with adherence to recommended infection control practices. Accurate knowledge about AIDS showed a weak (r = -.088) and nonsignificant relationship with dental hygienists' attitudes toward AIDS patients. Use of recommended infection control practices was found to be associated (r = -.20) with less fear concerning the treatment of AIDS patients. In addition, dental hygienists' infection control practices varied according to their perception of patient HIV status.

CONCLUSIONS

Since Pennsylvania dental hygienists, within the limitations of this study, appear not to follow CDC guidelines on proper and responsible operatory/laboratory aseptic techniques stringently, and to differentiate infection control procedures based on perceived patient HIV status, recommendations are that 1) the Commonwealth of Pennsylvania should mandate that all Pennsylvania-licensed dental hygienists take at least one state-approved course on operatory/laboratory infection control every two years to qualify for relicensure; 2) all dental and dental hygiene education institutions and professional organizations should place more emphasis on strict adherence to the various agency recommended clinical guidelines for infection control; and 3) all dental hygienists should continually strive to update their own knowledge of current infection control practices.

Syphilitic Aneurysm of Left Coronary Artery with Concurrent Aneurysm of a Sinus of Valsalva, and an Additional Case of Valsalva Aneurysm Alone

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