[Mapping as an Iterative Visualization Process: Insights into Regional Care Structures in the SARS-CoV-2 Pandemic]

OBJECTIVE

Little is known about the cooperation of different health care providers during the pandemic. The aim of this study was to develop a graphically mediated, deeper understanding of the processes involved, using a novel expert-supported visualization method, by taking a definite region in Baden-Württemberg as an example.

METHODS

The development of an overall picture ("mapping") of the pandemic situation in the Ulm/Alb-Donau district was based on the "Knowledge Visualization" method in several phases. First, semi-structured interviews were conducted with local players in the district of Ulm and the Alb-Donau. The visualized individual perspectives were then presented in a joint video conference. This was followed by a moderated discussion, with the aim to agree on common strategies for care in the pandemic. This process was documented with the help of a visulization expert ("Visionom") in the form of a professionally prepared overall picture ("mapping").

RESULTS

All players showed great motivation and appreciated getting to know the perspectives of other regional players. The iterative visualization was strongly activating and stimulated reflection processes. Personal responsibilities proved to be not always clear, communication problems were revealed. A wish to continue the initiated process was expressed.

CONCLUSION

Iterative visualizations can initiate implications at the level of action, metastructures and authorities. We recommend this method also for other questions related to local or regional structures.

Negatively Charged Peptide Nanofibrils from Immunoglobulin Light Chain Sequester Viral Particles but Lack Cell-Binding and Viral Transduction-Enhancing Properties

Positively charged naturally occurring or engineered peptide nanofibrils (PNF) are effective enhancers of lentiviral and retroviral transduction, an often rate-limiting step in gene transfer and gene therapy approaches. These polycationic PNF are thought to bridge the electrostatic repulsions between negatively charged membranes of virions and cells, thereby enhancing virion attachment to and infection of target cells. Here, we analyzed PNF, which are formed by the peptide AL1, that represents a fragment of an immunoglobulin light chain that causes systemic AL amyloidosis. We found that negatively charged AL1 PNF interact with viral particles to a comparable extent as positively charged PNF. However, AL1 PNF lacked cell-binding activity, and consequently, did not enhance retroviral infection. These findings show that virion capture and cell binding of PNF are mediated by different mechanisms, offering avenues for the design of advanced PNF with selective functions.

Supramolecular Mechanism of Viral Envelope Disruption by Molecular Tweezers

Broad-spectrum antivirals are powerful weapons against dangerous viruses where no specific therapy exists, as in the case of the ongoing SARS-CoV-2 pandemic. We discovered that a lysine- and arginine-specific supramolecular ligand (CLR01) destroys enveloped viruses, including HIV, Ebola, and Zika virus, and remodels amyloid fibrils in semen that promote viral infection. Yet, it is unknown how CLR01 exerts these two distinct therapeutic activities. Here, we delineate a novel mechanism of antiviral activity by studying the activity of tweezer variants: the “phosphate tweezer” CLR01, a “carboxylate tweezer” CLR05, and a “phosphate clip” PC. Lysine complexation inside the tweezer cavity is needed to antagonize amyloidogenesis and is only achieved by CLR01. Importantly, CLR01 and CLR05 but not PC form closed inclusion complexes with lipid head groups of viral membranes, thereby altering lipid orientation and increasing surface tension. This process disrupts viral envelopes and diminishes infectivity but leaves cellular membranes intact. Consequently, CLR01 and CLR05 display broad antiviral activity against all enveloped viruses tested, including herpesviruses, Measles virus, influenza, and SARS-CoV-2. Based on our mechanistic insights, we potentiated the antiviral, membrane-disrupting activity of CLR01 by introducing aliphatic ester arms into each phosphate group to act as lipid anchors that promote membrane targeting. The most potent ester modifications harbored unbranched C4 units, which engendered tweezers that were approximately one order of magnitude more effective than CLR01 and nontoxic. Thus, we establish the mechanistic basis of viral envelope disruption by specific tweezers and establish a new class of potential broad-spectrum antivirals with enhanced activity.

Storage-Dependent Generation of Potent Anti-ZIKV Activity in Human Breast Milk

Zika virus (ZIKV) causes congenital neurologic birth defects, notably microcephaly, and has been associated with other serious complications in adults. The virus has been detected in human breast milk and possible transmissions via breastfeeding have been reported. Breast milk is rich in nutrients and bio-active substances that might directly affect viral infectivity. Thus, here, we analyzed the effect of human breast milk on ZIKV infection. We observed that fresh human breast milk had no effect on ZIKV, but found that upon storage, milk effectively suppressed infection. The antiviral activity is present in the fat-containing cream fraction of milk and results in the destruction of the structural integrity of viral particles, thereby abrogating infectivity. The release of the factor is time dependent but varies with donors and incubation temperatures. The viral titer of milk that was spiked with ZIKV decreased considerably upon storage at 37 °C for 8 h, was lost entirely after 2 days of 4 °C storage, but was not affected at -20 °C. This suggests that cold storage of milk inactivates ZIKV and that the antiviral factor in milk may also be generated upon breastfeeding and limit this transmission route of ZIKV.

Structure, function and antagonism of semen amyloids

Amyloid fibrils are linear polypeptide aggregates with a cross-β structure. These fibrils are best known for their association with neurodegenerative diseases, such as Alzheimer's or Parkinson's, but they may also be used by living organisms as functional units, e.g. in the synthesis of melanin or in the formation of bacterial biofilms. About a decade ago, in a search for semen factors that modulate infection by HIV-1 (a sexually transmitted virus and the causative agent of the acquired immune deficiency syndrome (AIDS)), it was demonstrated that semen harbors amyloid fibrils capable of markedly increasing HIV infection rates. This discovery not only created novel opportunities to prevent sexual HIV-1 transmission but also stimulated research to unravel the natural role of these factors. We discuss here the identification of these intriguing structures, their molecular properties, and their effects on both sexually transmitted diseases and reproductive health. Moreover, we review strategies to antagonize semen amyloid to prevent sexual transmission of viruses.

Macromolecular Antiviral Agents against Zika, Ebola, SARS, and Other Pathogenic Viruses

Viral pathogens continue to constitute a heavy burden on healthcare and socioeconomic systems. Efforts to create antiviral drugs repeatedly lag behind the advent of pathogens and growing understanding is that broad‐spectrum antiviral agents will make strongest impact in future antiviral efforts. This work performs selection of synthetic polymers as novel broadly active agents and demonstrates activity of these polymers against Zika, Ebola, Lassa, Lyssa, Rabies, Marburg, Ebola, influenza, herpes simplex, and human immunodeficiency viruses. Results presented herein offer structure–activity relationships for these pathogens in terms of their susceptibility to inhibition by polymers, and for polymers in terms of their anionic charge and hydrophobicity that make up broad‐spectrum antiviral agents. The identified leads cannot be predicted based on prior data on polymer‐based antivirals and represent promising candidates for further development as preventive microbicides.

Semen amyloids participate in spermatozoa selection and clearance

Unlike other human biological fluids, semen contains multiple types of amyloid fibrils in the absence of disease. These fibrils enhance HIV infection by promoting viral fusion to cellular targets, but their natural function remained unknown. The similarities shared between HIV fusion to host cell and sperm fusion to oocyte led us to examine whether these fibrils promote fertilization. Surprisingly, the fibrils inhibited fertilization by immobilizing sperm. Interestingly, however, this immobilization facilitated uptake and clearance of sperm by macrophages, which are known to infiltrate the female reproductive tract (FRT) following semen exposure. In the presence of semen fibrils, damaged and apoptotic sperm were more rapidly phagocytosed than healthy ones, suggesting that deposition of semen fibrils in the lower FRT facilitates clearance of poor-quality sperm. Our findings suggest that amyloid fibrils in semen may play a role in reproduction by participating in sperm selection and facilitating the rapid removal of sperm antigens.

DOI:http://dx.doi.org/10.7554/eLife.24888.001

Seminal plasma, the fluid portion of semen, helps to transport sperm cells to the egg during sexual reproduction. Seminal plasma contains numerous proteins that help the sperm to survive and, in recent years, researchers discovered that it also harbours protein deposits known as amyloid fibrils.

Such protein deposits are generally associated with neurodegenerative diseases such as Alzheimer's and Parkinson’s disease, where a build-up of fibrils can damage the nervous system. Semen amyloids, however, are present in the absence of disease, but can boost infection by HIV and other sexually transmitted viruses, by shuttling virus particles to their target cells. Despite these damaging effects, some researchers had suggested that amyloids in semen could be beneficial for humans, though it was unclear what these benefits might be.

Roan et al. now set out to assess how semen amyloids affect human sperm activity. The results show that semen amyloids bind to damaged sperm cells and immobilize them, which are then quickly cleared away by immune cells. This could ensure that only the fittest sperm cells reach the egg.

These findings suggest that amyloids can potentially serve beneficial roles for reproduction. A next step will be to investigate how semen amyloids trap unwanted sperm and how immune cells know when to remove it. More research is needed to investigate if problems in these processes could lead to infertility in men.

DOI:http://dx.doi.org/10.7554/eLife.24888.002

Structural basis of the specificity of USP18 toward ISG15

Protein modification by ubiquitin and ubiquitin-like modifiers (Ubls) is counteracted by ubiquitin proteases and Ubl proteases, collectively termed DUBs. In contrast to other proteases of the ubiquitin-specific protease (USP) family, USP18 shows no reactivity toward ubiquitin but specifically deconjugates the interferon-induced Ubl ISG15. To identify the molecular determinants of this specificity, we solved the crystal structures of mouse USP18 alone and in complex with mouse ISG15. USP18 was crystallized in an open and a closed conformation, thus revealing high flexibility of the enzyme. Structural data, biochemical and mutational analysis showed that only the C-terminal ubiquitin-like domain of ISG15 is recognized and essential for USP18 activity. A critical hydrophobic patch in USP18 interacts with a hydrophobic region unique to ISG15, thus providing evidence that USP18's ISG15 specificity is mediated by a small interaction interface. Our results may provide a structural basis for the development of new drugs modulating ISG15 linkage.

NH2-terminal structural motifs in staphylokinase required for plasminogen activation

Staphylokinase (Sak) forms an inactive 1:1 stoichiometric complex with plasminogen which requires both conversion of plasminogen to plasmin and hydrolysis of the Lys10-Lys11 peptide bond of Sak to become a potent plasminogen activator (Schlott, B., Guhrs, K.-H., Hartmann, M., Rocker, A., and Collen, D. (1997) J. Biol. Chem. 272, 6067-6072). Exposure of a positively charged NH2-terminal amino acid after hydrolysis of Sak is a major determinant of the plasminogen-activating potential, but in itself is neither necessary nor sufficient. Here, the structural motifs of the NH2-terminal region Lys11-Gly-Asp-Asp-Ala-Ser16-Tyr-Phe-Glu of processed Sak, required for plasminogen activating potential, were studied by deletion and substitution mutagenesis. Expression in Escherichia coli of variants with deletion of 11, 14, 15, or 16 NH2-terminal amino acids yielded correctly processed but inactive molecules. Expression of their homologues with the NH2-terminal amino acid substituted with Lys-generated derivatives from which the NH2-terminal initiation Met was no longer removed, yielding inactive (</= 10%) Sak42DDeltaN11(M),G12K, active (>50%) Sak42DDeltaN14(M), A15K and Sak42DDeltaN15(M),S16K, and inactive Sak42DDeltaN16(M),Y17K. Lys variants without NH2-terminal Met, generated from fusion proteins in which a His6 tag and a factor Xa recognition sequence were linked to the NH2 terminus of the Sak variants, were indistinguishable from their NH2-terminal Met-containing counterparts. All variants studied had intact affinities for plasminogen as measured by biospecific interaction analysis. The activity of Sak42DDeltaN11(M),G12K could be restored by additional substitution of both Asp13 and Asp14 with Asn, yielding active Sak42DDeltaN11(M),G12K, D13N, D14N, whereas substitution in Sak42DDeltaN16(M),Y17K of Phe18 and Glu19 with Asn yielded inactive Sak42DDeltaN16(M),Y17K,F18N,E19N. These data, in combination with the recent finding that the 20 NH2-terminal amino acids of Sak lack secondary structure, suggest that the NH2-terminal region of Sak is not required for binding to plasmin/plasminogen, but that a positively charged amino acid in the ultimate or penultimate NH2-terminal position corresponding to amino acids 11-16 of this flexible region participates in the reconfiguration of the active site of the plasmin molecule to endow it with plasminogen-activating potential.

Staphylokinase requires NH2-terminal proteolysis for plasminogen activation

Staphylokinase (Sak), a single-chain protein comprising 136 amino acids with NH2-terminal sequence,SSSFDKGKYKKGDDA forms a complex with plasmin, that is endowed with plasminogen activating properties. Plasmin is presumed to process mature (high molecular weight, HMW) Sak to low molecular weight derivatives (LMW-Sak), primarily by hydrolyzing the Lys10-Lys11 peptide bond, but the kinetics of plasminogen activation by HMW-Sak and LMW-Sak are very similar. Here, the requirement of NH2-terminal proteolysis of Sak for the induction of plasminogen activating potential was studied by mutagenesis of Lys10 and Lys11 in combination with NH2-terminal microsequence analysis of equimolar mixtures of Sak and plasminogen and determination of kinetic parameters of plasminogen activation by catalytic amounts of Sak. Substitution of Lys10 with Arg did not affect processing of the Arg10-Lys11 site nor plasminogen activation, whereas substitution with His resulted in cleavage of the Lys11-Gly12 peptide bond and abolished plasminogen activation. Substitution of Lys11 with Arg did not affect Lys10-Arg11 processing or plasminogen activation, whereas replacement with His did not prevent Lys10-His11 hydrolysis but abolished plasminogen activation. Substitution of Lys11 with Cys yielded an inactive processed derivative which was fully activated by aminoethylation. Deletion of the 10 NH2-terminal amino acids did not affect plasminogen activation, but additional deletion of Lys11 eliminated plasminogen activation. Thus generation of plasminogen activator potential in Sak proceeds via plasmin-mediated removal of the 10 NH2-terminal amino acids with exposure of Lys11 as the new NH2 terminus. This provides a structural basis for the hypothesis, derived from kinetic measurements, that plasminogen activation by Sak needs to be primed by plasmin and a mechanism for the high fibrin selectivity of Sak in a plasma milieu.

Functional significance of NH2- and COOH-terminal regions of staphylokinase in plasminogen activation

Structure/function relationships in the activation of plasminogen with staphylokinase were studied using mutants of recombinant staphylokinase (Sak42D). Deletion of up to 10 NH2-terminal amino acids (Sak42D delta N10) did not affect plasminogen activation, but removal of 11 amino acids completely abolished the ability to activate plasminogen. Elimination of potential plasmin cleavage sites in the NH2-terminal region yielding mutants Sak42D(K8H,K10H,K11H) and Sak42D(K6H,K8H,K11H) did not alter the rate of the exposure of a proteolytically active site (amidolytic activity) in equimolar mixtures with plasminogen, but destroyed the plasminogen activator properties of these muteins. Deleting two residues following the preferred processing site at position 10 (Sak42 delta (K11,G12)) resulted in a mutein also inactive in plasminogen activation. Removal of the COOH-terminal Lys136, yielding Sak42D delta C1, or of Lys135 and Lys136 in Sak42D delta C2 resulted in proteins with strongly reduced plasminogen activation capacity. In contrast, substitution of Lys135 and Lys136 with Ala in Sak42D(K135A,K136A) did not affect activation. Cyanogen bromide cleavage of Sak42D(M26L,E61M,D82E) produced a 61 amino acid NH2-terminal and a 65 amino acid COOH-terminal fragment which did not activate plasminogen, but bound to plasminogen with affinity constants Ka of 4.0 x 10(5) M-1 and 1.4 x 10(7) M-1, respectively (as compared to a Ka of 1.1 x 10(8) M-1 for Sak42D). These results indicate that Lys11 and the COOH-terminal region of staphylokinase play a key role in the activation of plasminogen.