The channel activities of the full-length prion and truncated proteins

Prion disease is a fatal neurodegenerative disorder, in which the cellular prion protein PrPC is converted to a misfolded prion which in turn is hypothesized to permeabilize cellular membranes. The pathways leading to toxicity in prion disease are not yet completely elucidated and whether it also includes formation of membrane pores remains to be answered. Prion protein consists of two domains: a globular domain (GD) and a flexible N-terminus (FT) domain. Although a proximal nine polybasic amino acid (FT(23-31)) sequence of FT is a prerequisite for cellular membrane permeabilization, other functional domain regions may influence FT(23-31) and its permeabilization. By using single-channel electrical recordings, we reveal that FT(23-50) dominates the membrane permeabilization within the full-length mouse PrP (mPrP(23-230)). The other domain of FT(51-110) or C-terminal domain down-regulates the channel activity of FT(23-50) and the full-length mouse PrP (mPrP(23-230)). The addition of prion mimetic antibody, POM1 significantly enhances mPrP(23-230) membrane permeabilization, whereas POM1-Y104A, a POM1 mutant that binds to PrP but cannot elicit toxicity has negligible effect on membrane permeabilization. Additionally, anti-N-terminal antibody POM2 or Cu2+ stabilizes FT domain, thus provoking FT(23-110) channel activity. Furthermore, our setup provides a more direct method without an external fused protein to study the channel activity of truncated PrP in the lipid membranes. We therefore hypothesize that the primary N-terminal residues are essential for membranes permeabilization and other functional segments play a vital role to modulate the pathological effects of PrP-medicated neurotoxicity. This may yield essential insights into molecular mechanisms of prion neurotoxicity to cellular membranes in prion disease.

Biophysical characterization of the homodimers of HomA and HomB, outer membrane proteins of Helicobacter pylori

Helicobacter pylori is a Gram-negative bacterium that causes chronic inflammations in the stomach area and is involved in ulcers, which can develop into gastric malignancies. H. pylori attaches and colonizes to the human epithelium using some of their outer membrane proteins (OMPs). HomB and HomA are the most studied OMPs from H. pylori as they play a crucial role in adherence, hyper biofilm formation, antibiotic resistance and are also associated with severe gastric malignancies. The role of HomA and HomB in pathogenesis concerning their structure and function has not been evaluated yet. In the present study, we explored the structural aspect of HomA and HomB proteins using various computational, biophysical and small-angle X-ray scattering (SAXS) techniques. Interestingly, the in-silico analysis revealed that HomA/B consists of 8 discontinuous N and C terminal β-strands forming a small β-barrel, along with a large surface-exposed globular domain. Further, biophysical experiments suggested that HomA and HomB are dimeric and most likely the cysteine residues present on surface-exposed loops participate in protein–protein interactions. Our study provides essential structural information of unexplored proteins of the Hom family that can help in a better understanding of H. pylori pathogenesis.

Escherichia coli O127 group 4 capsule proteins assemble at the outer membrane

Enteropathogenic Escherichia coli O127 is encapsulated by a protective layer of polysaccharide made of the same strain specific O-antigen as the serotype lipopolysaccharide. Seven genes encoding capsule export functions comprise the group 4 capsule (gfc) operon. Genes gfcE, etk and etp encode homologs of the group 1 capsule secretion system but the upstream gfcABCD genes encode unknown functions specific to group 4 capsule export. We have developed an expression system for the large-scale production of the outer membrane protein GfcD. Contrary to annotations, we find that GfcD is a non-acylated integral membrane protein. Circular dichroism spectroscopy, light-scattering data, and the HHomp server suggested that GfcD is a monomeric β-barrel with 26 β-strands and an internal globular domain. We identified a set of novel protein-protein interactions between GfcB, GfcC, and GfcD, both in vivo and in vitro, and quantified the binding properties with isothermal calorimetry and biolayer interferometry. GfcC and GfcB form a high-affinity heterodimer with a KD near 100 nM. This heterodimer binds to GfcD (KD = 28 μM) significantly better than either GfcB or GfcC alone. These gfc proteins may form a complex at the outer membrane for group 4 capsule secretion or for a yet unknown function.

Epigallocatechin-3-Gallate as a Novel Vaccine Adjuvant

Vaccine adjuvants from natural resources have been utilized for enhancing vaccine efficacy against infectious diseases. This study examined the potential use of catechins, polyphenolic materials derived from green tea, as adjuvants for subunit and inactivated vaccines. Previously, catechins have been documented to have irreversible virucidal function, with the possible applicability in the inactivated viral vaccine platform. In a mouse model, the coadministration of epigallocatechin-3-gallate (EGCG) with influenza hemagglutinin (HA) antigens induced high levels of neutralizing antibodies, comparable to that induced by alum, providing complete protection against the lethal challenge. Adjuvant effects were observed for all types of HA antigens, including recombinant full-length HA and HA1 globular domain, and egg-derived inactivated split influenza vaccines. The combination of alum and EGCG further increased neutralizing (NT) antibody titers with the corresponding hemagglutination inhibition (HI) titers, demonstrating a dose-sparing effect. Remarkably, EGCG induced immunoglobulin isotype switching from IgG1 to IgG2a (approximately >64–700 fold increase), exerting a more balanced TH1/TH2 response compared to alum. The upregulation of IgG2a correlated with significant enhancement of antibody-dependent cellular cytotoxicity (ADCC) function (approximately 14 fold increase), providing a potent effector-mediated protection in addition to NT and HI. As the first report on a novel class of vaccine adjuvants with built-in virucidal activities, the results of this study will help improve the efficacy and safety of vaccines for pandemic preparedness.

Archaeal origins of gamete fusion

Sexual reproduction in Eukarya consists of genome reduction by meiosis and subsequent gamete fusion. The presence of meiotic genes in Archaea and Bacteria suggests that prokaryotic DNA repair mechanisms evolved towards meiotic recombination. However, the evolutionary origin of gamete fusion is less clear because fusogenic proteins resembling those found in Eukarya have so far not been identified in prokaryotes. Here, using bioinformatics, we identified archaeal genes encoding candidates of fusexins, a superfamily of fusogens mediating somatic and gamete fusion in multiple eukaryotic lineages. Crystallographic structure determination of a candidate archaeal FusexinA reveals an archetypical trimeric fusexin architecture with novel features such as a six-helix bundle and an additional globular domain. We demonstrate that ectopically expressed FusexinA can fuse mammalian cells, and that this process involves the additional domain and a more broadly conserved fusion loop. Genome content analyses reveal that archaeal fusexins genes are within integrated mobile elements. Finally, evolutionary analyses place these archaeal fusogens as the founders of the fusexin superfamily. Based on these findings, we propose a new hypothesis on the origins of eukaryotic sex where an archaeal fusexin, originally used by selfish elements for horizontal transmission, was repurposed to enable gamete fusion.

Short tail stories: the hirudin-like factors HLF6 and HLF7 of the Asian medicinal leech, Hirudinaria manillensis

The leech-derived hirudins and hirudin-like factors (HLFs) share a common molecule structure: a short N-terminus, a central globular domain, and an elongated C-terminal tail. All parts are important for function. HLF6 and HLF7 were identified in the Asian medicinal leech, Hirudinaria manillensis. The genes of both factors encode putative splice variants that differ in length and composition of their respective C-terminal tails. In either case, the tails are considerably shorter compared to hirudins. Here we describe the functional analyses of the natural splice variants and of synthetic variants that comprise an altered N-terminus and/or a modified central globular domain. All natural splice variants of HLF6 and HLF7 display no detectable thrombin-inhibitory potency. In contrast, some synthetic variants effectively inhibit thrombin, even with tails as short as six amino acid residues in length. Our data indicate that size and composition of the C-terminal tail of hirudins and HLFs can vary in a great extent, yet the full protein may still retain the ability to inhibit thrombin.

Molecular Dynamics Simulations of resistin and RELMβ proteins: Insight into structural dynamics

Diabetes mellitus and high levels of resistin are risk factors for COVID-19, suggest- ing a shared mechanism for their contribution to the increased severity of COVID-19. Resistin belongs to the family of resistin-like molecules (RELMs) whose implications for inflammatory and metabolic dysfunctions warrant its study in order to shed light on the etiology of these concerning pathologies. In this work, our objective is to char- acterize the structural dynamics of the reported crystallized resistin-like molecules. We performed molecular dynamics simulations of all-atom solvated protein at physiological and high temperatures for the three mouse structures reported so far. We found that in all the structures studied, there is a loss of helicity as a first step of protein denat- uration. There is a high stability of the globular β-sheet domain in resistin protein structures that is not conserved for RELMβ. At high temperature, we found a partial interconversion of α-helices into β-sheets in all proteins, indicating that this propensity is not only found during aggregation but also heating. We had been able to identify a largely persistent hydrogen-bond network shared by all the proteins in the interchain globular domain at room temperature. This network of hydrogen bonds is conserved considerably at high temperature in resistin structures, but not in RELMβ. These findings may guide future studies to increase our understanding of the different and shared mechanisms of action of RELMs.

Targeting the Achilles Heel of FtsZ: The Interdomain Cleft

Widespread antimicrobial resistance among bacterial pathogens is a serious threat to public health. Thus, identification of new targets and development of new antibacterial agents are urgently needed. Although cell division is a major driver of bacterial colonization and pathogenesis, its targeting with antibacterial compounds is still in its infancy. FtsZ, a bacterial cytoskeletal homolog of eukaryotic tubulin, plays a highly conserved and foundational role in cell division and has been the primary focus of research on small molecule cell division inhibitors. FtsZ contains two drug-binding pockets: the GTP binding site situated at the interface between polymeric subunits, and the inter-domain cleft (IDC), located between the N-terminal and C-terminal segments of the core globular domain of FtsZ. The majority of anti-FtsZ molecules bind to the IDC. Compounds that bind instead to the GTP binding site are much less useful as potential antimicrobial therapeutics because they are often cytotoxic to mammalian cells, due to the high sequence similarity between the GTP binding sites of FtsZ and tubulin. Fortunately, the IDC has much less sequence and structural similarity with tubulin, making it a better potential target for drugs that are less toxic to humans. Over the last decade, a large number of natural and synthetic IDC inhibitors have been identified. Here we outline the molecular structure of IDC in detail and discuss how it has become a crucial target for broad spectrum and species-specific antibacterial agents. We also outline the drugs that bind to the IDC and their modes of action.

Abstract P454: The Interaction Of P300 With Brg1 Acetylated The Histone H3 Globular Domain In Heart Failure

Background: Epigenetic regulatory mechanisms such as histone post-translational modifications are involved in the development of heart failure. Although the acetylation of tail domains, such as H3K9, has been extensively studied, that of H3K122, the globular domain, has received much less attention. Acetylation of the globular domain directly activates transcription by destabilizing histone-DNA binding. However, the acetylation of these domains during the transition from left ventricular hypertrophy (LVH) to heart failure (HF) remains unknown. Methods and Results: Primary cultured cardiomyocytes prepared from neonatal rats were treated with phenylephrine (PE). PE increased the acetylation of H3K9 and H3K122. The acetylation of H3K9 and H3K122 on the promoters of ANF and BNP, which are hypertrophic reaction genes, was increased in cardiomyocyte hypertrophy. To investigate whether the transcriptional coactivator p300 is involved in the acetylation of H3K9 and H3K122, p300 knockdown was used. p300 knockdown suppressed PE-induced cardiomyocyte hypertrophy and the acetylation of H3K9 and H3K122. In Dahl-salt sensitive rats, in vivo chromatin-immunoprecipitation assays revealed that the acetylation of H3K9 on the promoter of the hypertrophic response genes was significantly increased in LVH, but the acetylation of H3K122 was not increased in LVH. However, H3K122 acetylation was significantly increased in HF. On the other hand, there was no difference in the amount of recruitment of p300 in LVH and HF. Interestingly, immunoprecipitation-WB showed that binding of p300 with BRG1, a key component of the SWI/SNF complex, was enhanced in HF. The recruitment of BRG1 increased significantly in HF compared to LVH. Moreover, PFI-3, a BRG1 inhibitor, significantly suppressed a PE-induced increase in cardiomyocyte surface area, the mRNA levels of ANF and BNP, and the acetylation of H3K9 and H3K122 in cultured cardiomyocytes. Conclusion: This study demonstrates that the acetylation of H3K122 is enhanced via the interaction of p300 and BRG1 in heart failure, providing novel insights into the epigenetic regulatory mechanism governing transcriptional activity in these processes.