Viral membrane penetration: lytic activity of a nodaviral fusion peptide

Meet the IUPAB Councilor-Hans-Joachim Galla

As one of the twelve Councilors, it is my pleasure to provide a short biographical sketch for the readers of Biophys. Rev. and for the members of the Biophysical Societies. I have been a member of the council in the former election period. Moreover, I served since decades in the German Biophysical Society (DGfB) as board member, secretary, vice president, and president. I hold a diploma degree in chemistry as well as PhD from the University of Göttingen. The experimental work for both qualifications has been performed at the Max Planck Institute for Biophysical Chemistry in Göttingen under the guidance of Erich Sackmann and the late Herman Träuble. When E. Sackmann moved to the University of Ulm, I joined his group as a research assistant performing my independent research on structure and dynamics of biological and artificial membranes and qualified for the “habilitation” thesis in Biophysical Chemistry. I have spent a research year at Stanford University supported by the Deutsche Forschungsgemeinschaft (DFG) and after coming back to Germany, I was appointed as a Heisenberg Fellow by the DFG and became Professor in Biophysical Chemistry in the Chemistry Department of the University of Darmstadt. Since 1990, I spent my career at the Institute for Biochemistry of the University of Muenster as full Professor and Director of the institute. I have trained numerous undergraduate, 150 graduate, and postdoctoral students from chemistry, physics, and also pharmacy as well as biology resulting in more than 350 published papers including reviews and book articles in excellent collaboration with colleagues from different academic disciplines in our university and also internationally, e.g., as a guest professor at the Chemistry Department of the Chinese Academy of Science in Beijing.

Incorporation of Endosomolytic Peptides with Varying Disruption Mechanisms into EGFR-Targeted Protein Conjugates: The Effect on Intracellular Protein Delivery and EGFR Specificity in Breast Cancer Cells

Intracellular delivery of protein therapeutics remains a significant challenge limiting the majority of clinically available protein drugs to extracellular targets. Strategies to deliver proteins to subcellular compartments have traditionally relied on cell-penetrating peptides, which can drive enhanced internalization but exhibit unreliable activity and are rarely able to target specific cells, leading to off-target effects. Moreover, few design rules exist regarding the relative efficacy of various endosomal escape strategies in proteins. Accordingly, we developed a simple fusion modification approach to incorporate endosomolytic peptides onto epidermal growth factor receptor (EGFR)-targeted protein conjugates and performed a systematic comparison of the endosomal escape efficacy, mechanism of action, and capacity to maintain EGFR-targeting specificity of conjugates modified with four different endosomolytic sequences of varying modes of action (Aurein 1.2, GALA, HA2, and L17E). Use of the recently developed Gal8-YFP assay indicated that the fusion of each endosomolytic peptide led to enhanced endosomal disruption. Additionally, the incorporation of each endosomolytic peptide increased the half-life of the internalized protein and lowered lysosomal colocalization, further supporting the membrane-disruptive capacity. Despite this, only EGFR-targeted conjugates modified with Aurein 1.2 or GALA maintained EGFR specificity. These results thus demonstrated that the choice of endosomal escape moiety can substantially affect targeting capability, cytotoxicity, and bioactivity and provided important new insights into endosomolytic peptide selection for the design of targeted protein delivery systems.

Influence of membrane composition on the binding and folding of a membrane lytic peptide from the non-enveloped flock house virus

Using a combination of coarse-grained and atomistic molecular dynamics simulations we have investigated the membrane binding and folding properties of the membrane lytic peptide of Flock House virus (FHV). FHV is an animal virus and an excellent model system for studying cell entry mechanisms in non-enveloped viruses. FHV undergoes a maturation event where the 44 C-terminal amino acids are cleaved from the major capsid protein, forming the membrane lytic (γ) peptides. Under acidic conditions, γ is released from the capsid interior allowing the peptides to bind and disrupt membranes. The first 21 N-terminal residues of γ, termed γ₁, have been resolved in the FHV capsid structure and γ₁ has been the subject of in vitro studies. γ₁ is structurally dynamic as it adopts helical secondary structure inside the capsid and on membranes, but it is disordered in solution. In vitro studies have shown the binding free energies to POPC or POPG membranes are nearly equivalent, but binding to POPC is enthalpically driven, while POPG binding is entropically driven. Through coarse-grained and multiple microsecond all-atom simulations the membrane binding and folding properties of γ₁ are investigated against homogeneous and heterogeneous bilayers to elucidate the dependence of the microenvironment on the structural properties of γ₁. Our studies provide a rationale for the thermodynamic data and suggest binding of γ₁ to POPG bilayers occurs in a disordered state, but γ₁ must adopt a helical conformation when binding POPC bilayers.

Phosphatidylserine lipids and membrane order precisely regulate the activity of Polybia-MP1 peptide

Polybia-MP1 (IDWKKLLDAAKQIL-NH₂) is a lytic peptide from the Brazilian wasp venom with known anti-cancer properties. Previous evidence indicates that phosphatidylserine (PS) lipids are relevant for the lytic activity of MP1. In agreement with this requirement, phosphatidylserine lipids are translocated to the outer leaflet of cells, and are available for MP1 binding, depending on the presence of liquid-ordered domains. Here, we investigated the effect of PS on MP1 activity when this lipid is reconstituted in membranes of giant or large liposomes with different lipid-phase states. By monitoring the membrane and soluble luminal content of giant unilamellar vesicles (GUVs), using fluorescence confocal microscopy, we were able to determine that MP1 has a pore-forming activity at the membrane level. Liquid-ordered domains, which were phase-separated within the membrane of GUVs, influenced the pore-forming activity of MP1. Experiments evaluating the membrane-binding and lytic activity of MP1 on large unilamellar vesicles (LUVs), with the same lipid composition as GUVs, demonstrated that there was synergy between liquid-ordered domains and PS, which enhanced both activities. Based on our findings, we propose that the physicochemical properties of cancer cell membranes, which possess a much higher concentration of PS than normal cells, renders them susceptible to MP1 binding and lytic pore formation. These results can be correlated with MP1's potent and selective anti-cancer activity and pave the way for future research to develop cancer therapies that harness and exploit the properties of MP1.

Comparison between the behavior of different hydrophobic peptides allowing membrane anchoring of proteins

Membrane binding of proteins such as short chain dehydrogenase reductases or tail-anchored proteins relies on their N- and/or C-terminal hydrophobic transmembrane segment. In this review, we propose guidelines to characterize such hydrophobic peptide segments using spectroscopic and biophysical measurements. The secondary structure content of the C-terminal peptides of retinol dehydrogenase 8, RGS9-1 anchor protein, lecithin retinol acyl transferase, and of the N-terminal peptide of retinol dehydrogenase 11 has been deduced by prediction tools from their primary sequence as well as by using infrared or circular dichroism analyses. Depending on the solvent and the solubilization method, significant structural differences were observed, often involving α-helices. The helical structure of these peptides was found to be consistent with their presumed membrane binding. Langmuir monolayers have been used as membrane models to study lipid-peptide interactions. The values of maximum insertion pressure obtained for all peptides using a monolayer of 1,2-dioleoyl-sn-glycero-3-phospho-ethanolamine (DOPE) are larger than the estimated lateral pressure of membranes, thus suggesting that they bind membranes. Polarization modulation infrared reflection absorption spectroscopy has been used to determine the structure and orientation of these peptides in the absence and in the presence of a DOPE monolayer. This lipid induced an increase or a decrease in the organization of the peptide secondary structure. Further measurements are necessary using other lipids to better understand the membrane interactions of these peptides.

Learning from the viral journey: how to enter cells and how to overcome intracellular barriers to reach the nucleus

Viruses deliver their genome into host cells where they subsequently replicate and multiply. A variety of relevant strategies have evolved by which viruses gain intracellular access and utilize cellular machinery for the synthesis of their genome. Therefore, the viral journey provides insight into the cell's trafficking machinery and how it can be best exploited to improve nonviral gene delivery systems. This review summarizes viral internalization pathways and intracellular trafficking of viruses, with an emphasis on the endosomal escape processes of nonenveloped viruses. Intracellular events from viral entry through nuclear delivery of the viral complementary DNA are also discussed.

Structure of a membrane-binding domain from a non-enveloped animal virus: insights into the mechanism of membrane permeability and cellular entry

The gamma(1)-peptide is a 21-residue lipid-binding domain from the non-enveloped Flock House virus (FHV). Unlike enveloped viruses, the entry of non-enveloped viruses into cells is believed to occur without membrane fusion. In this study, we performed NMR experiments to establish the solution structure of a membrane-binding peptide from a small non-enveloped icosahedral virus. The three-dimensional structure of the FHV gamma(1)-domain was determined at pH 6.5 and 4.0 in a hydrophobic environment. The secondary and tertiary structures were evaluated in the context of the capacity of the peptide for permeabilizing membrane vesicles of different lipid composition, as measured by fluorescence assays. At both pH values, the peptide has a kinked structure, similar to the fusion domain from the enveloped viruses. The secondary structure was similar in three different hydrophobic environments as follows: water/trifluoroethanol, SDS, and membrane vesicles of different compositions. The ability of the peptide to induce vesicle leakage was highly dependent on the membrane composition. Although the gamma-peptide shares some structural properties to fusion domains of enveloped viruses, it did not induce membrane fusion. Our results suggest that small protein components such as the gamma-peptide in nodaviruses (such as FHV) and VP4 in picornaviruses have a crucial role in conducting nucleic acids through cellular membranes and that their structures resemble the fusion domains of membrane proteins from enveloped viruses.