Jan Felix

Historical epidemiology of hepatitis C virus (HCV) in selected countries

Chronic infection with hepatitis C virus (HCV) is a leading indicator for liver disease. New treatment options are becoming available, and there is a need to characterize the epidemiology and disease burden of HCV. Data for prevalence, viremia, genotype, diagnosis and treatment were obtained through literature searches and expert consensus for 16 countries. For some countries, data from centralized registries were used to estimate diagnosis and treatment rates. Data for the number of liver transplants and the proportion attributable to HCV were obtained from centralized databases. Viremic prevalence estimates varied widely between countries, ranging from 0.3% in Austria, England and Germany to 8.5% in Egypt. The largest viremic populations were in Egypt, with 6 358 000 cases in 2008 and Brazil with 2 106 000 cases in 2007. The age distribution of cases differed between countries. In most countries, prevalence rates were higher among males, reflecting higher rates of injection drug use. Diagnosis, treatment and transplant levels also differed considerably between countries. Reliable estimates characterizing HCV‐infected populations are critical for addressing HCV‐related morbidity and mortality. There is a need to quantify the burden of chronic HCV infection at the national level.

Strategies to manage hepatitis C virus (HCV) disease burden

The number of hepatitis C virus (HCV) infections is projected to decline while those with advanced liver disease will increase. A modeling approach was used to forecast two treatment scenarios: (i) the impact of increased treatment efficacy while keeping the number of treated patients constant and (ii) increasing efficacy and treatment rate. This analysis suggests that successful diagnosis and treatment of a small proportion of patients can contribute significantly to the reduction of disease burden in the countries studied. The largest reduction in HCV‐related morbidity and mortality occurs when increased treatment is combined with higher efficacy therapies, generally in combination with increased diagnosis. With a treatment rate of approximately 10%, this analysis suggests it is possible to achieve elimination of HCV (defined as a >90% decline in total infections by 2030). However, for most countries presented, this will require a 3–5 fold increase in diagnosis and/or treatment. Thus, building the public health and clinical provider capacity for improved diagnosis and treatment will be critical.

The bacterial antitoxin HipB establishes a ternary complex with operator DNA and phosphorylated toxin HipA to regulate bacterial persistence

Nearly all bacteria exhibit a type of phenotypic growth described as persistence that is thought to underlie antibiotic tolerance and recalcitrant chronic infections. The chromosomally encoded high-persistence (Hip) toxin–antitoxin proteins HipASO and HipBSO from Shewanella oneidensis, a proteobacterium with unusual respiratory capacities, constitute a type II toxin–antitoxin protein module. Here we show that phosphorylated HipASO can engage in an unexpected ternary complex with HipBSO and double-stranded operator DNA that is distinct from the prototypical counterpart complex from Escherichia coli. The structure of HipBSO in complex with operator DNA reveals a flexible C-terminus that is sequestered by HipASO in the ternary complex, indicative of its role in binding HipASO to abolish its function in persistence. The structure of HipASO in complex with a non-hydrolyzable ATP analogue shows that HipASO autophosphorylation is coupled to an unusual conformational change of its phosphorylation loop. However, HipASO is unable to phosphorylate the translation factor Elongation factor Tu, contrary to previous reports, but in agreement with more recent findings. Our studies suggest that the phosphorylation state of HipA is an important factor in persistence and that the structural and mechanistic diversity of HipAB modules as regulatory factors in bacterial persistence is broader than previously thought.

Mechanisms of immunomodulation by mammalian and viral decoy receptors: insights from structures

Immune responses are regulated by effector cytokines and chemokines that signal through cell surface receptors. Mammalian decoy receptors — which are typically soluble or inactive versions of cell surface receptors or soluble protein modules termed binding proteins — modulate and antagonize signalling by canonical effector–receptor complexes. Viruses have developed a diverse array of molecular decoys to evade host immune responses; these include viral homologues of host cytokines, chemokines and chemokine receptors; variants of host receptors with new functions; and novel decoy receptors that do not have host counterparts. Over the past decade, the number of known mammalian and viral decoy receptors has increased considerably, yet a comprehensive curation of the corresponding structure–mechanism relationships has not been carried out. In this Review, we provide a comprehensive resource on this topic with a view to better understanding the roles and evolutionary relationships of mammalian and viral decoy receptors, and the opportunities for leveraging their therapeutic potential.

Structure and Assembly Mechanism of the Signaling Complex Mediated by Human CSF-1.

Human colony-stimulating factor 1 receptor (hCSF-1R) is unique among the hematopoietic receptors because it is activated by two distinct cytokines, CSF-1 and interleukin-34 (IL-34). Despite ever-growing insights into the central role of hCSF-1R signaling in innate and adaptive immunity, inflammatory diseases, and cancer, the structural basis of the functional dichotomy of hCSF-1R has remained elusive. Here, we report crystal structures of ternary complexes between hCSF-1 and hCSF-1R, including their complete extracellular assembly, and propose a mechanism for the cooperative human CSF-1:CSF-1R complex that relies on the adoption by dimeric hCSF-1 of an active conformational state and homotypic receptor interactions. Furthermore, we trace the cytokine-binding duality of hCSF-1R to a limited set of conserved interactions mediated by functionally equivalent residues on CSF-1 and IL-34 that play into the geometric requirements of hCSF-1R activation, and map the possible mechanistic consequences of somatic mutations in hCSF-1R associated with cancer.

Structural basis of GM-CSF and IL-2 sequestration by the viral decoy receptor GIF

Subversion of the host immune system by viruses is often mediated by molecular decoys that sequester host proteins pivotal to mounting effective immune responses. The widespread mammalian pathogen parapox Orf virus deploys GIF, a member of the poxvirus immune evasion superfamily, to antagonize GM-CSF (granulocyte macrophage colony-stimulating factor) and IL-2 (interleukin-2), two pleiotropic cytokines of the mammalian immune system. However, structural and mechanistic insights into the unprecedented functional duality of GIF have remained elusive. Here we reveal that GIF employs a dimeric binding platform that sequesters two copies of its target cytokines with high affinity and slow dissociation kinetics to yield distinct complexes featuring mutually exclusive interaction footprints. We illustrate how GIF serves as a competitive decoy receptor by leveraging binding hotspots underlying the cognate receptor interactions of GM-CSF and IL-2, without sharing any structural similarity with the cytokine receptors. Our findings contribute to the tracing of novel molecular mimicry mechanisms employed by pathogenic viruses.

Plasticity and cooperativity of cytokine-receptor assemblies at the cell surface

Hybrid approaches in structural biology have had a tremendous impact on our ability to tackle complex biological problems including large and flexible protein-protein assemblies. We have been employing creative combinations of X-ray crystallography, Small-angle Xray Scattering (SAXS) and electron microscopy in conjunction with molecular interaction studies and cellular interrogation of the systems under study to elucidate the structural and mechanistic principles underlying diverse cytokine-receptor assemblies. Our studies have revealed the unexpected structural diversity of such assemblies, and have established that structural plasticity and molecular cooperativity both at the level of the cytokines and the receptors play critical roles in the assembly of signaling complexes. My presentation will provide a coherent overview of how we have tackled cytokine-receptor signalling complexes in a hypothesisdriven manner with the help of hybrid approaches in structural biology.