Phospholipase A2 way to hydrolysis: Dint formation, hydrophobic mismatch, and lipid exclusion

Hydrolysis of phospholipid monolayers by phospholipase A2 revealed by heterodyne-detected sum frequency generation (HD-SFG) spectroscopy

Phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 acyl ester linkage in phospholipid, producing lysophospholipid and fatty acid in the presence of Ca2+. The hydrolysis mediated by PLA2 has attracted much interest in various fields, such as pharmacy and biotechnology. It is recognized that PLA2 cannot hydrolyze phospholipid monolayers at high surface coverage. However, the origin of different PLA2 activities is not fully understood yet. The present study investigated the interaction between DPPC (16:0 PC) monolayer and PLA2 using heterodyne-detected sum frequency generation spectroscopy, which is interface-specific spectroscopy and highly sensitive to molecular symmetry based on a second-order nonlinear optical process. It was revealed that PLA2 adsorbs to the DPPC monolayer on the aqueous solution surface only when the surface coverage is low. The adsorption at the low surface coverage significantly changes the interfacial structures of PLA2 and the hydration, which are stabilized by the presence of Ca2+. Therefore, the restriction of the hydrolysis of phospholipid monolayers at high surface coverage can be rationalized by the inhabitation of the PLA2 adsorption. The present study deepens our molecular-level understanding of the hydrolysis of phospholipids by PLA2.

Effects of Nitro-Oxidative Stress on Biomolecules: Part 1-Non-Reactive Molecular Dynamics Simulations

Plasma medicine, or the biomedical application of cold atmospheric plasma (CAP), is an expanding field within plasma research. CAP has demonstrated remarkable versatility in diverse biological applications, including cancer treatment, wound healing, microorganism inactivation, and skin disease therapy. However, the precise mechanisms underlying the effects of CAP remain incompletely understood. The therapeutic effects of CAP are largely attributed to the generation of reactive oxygen and nitrogen species (RONS), which play a crucial role in the biological responses induced by CAP. Specifically, RONS produced during CAP treatment have the ability to chemically modify cell membranes and membrane proteins, causing nitro-oxidative stress, thereby leading to changes in membrane permeability and disruption of cellular processes. To gain atomic-level insights into these interactions, non-reactive molecular dynamics (MD) simulations have emerged as a valuable tool. These simulations facilitate the examination of larger-scale system dynamics, including protein-protein and protein-membrane interactions. In this comprehensive review, we focus on the applications of non-reactive MD simulations in studying the effects of CAP on cellular components and interactions at the atomic level, providing a detailed overview of the potential of CAP in medicine. We also review the results of other MD studies that are not related to plasma medicine but explore the effects of nitro-oxidative stress on cellular components and are therefore important for a broader understanding of the underlying processes.

Advances in peripheral blood biomarkers of patients with Alzheimer's disease: Moving closer to personalized therapies

Recently, measurable peripheral biomarkers in the plasma of patients with Alzheimer's disease (AD) have gained considerable clinical interest. Several studies have identified one or more blood signatures that may facilitate the development of novel diagnostic and therapeutic strategies. For instance, changes in peripheral amyloid β42 (Aβ42) levels have been largely investigated in patients with AD and correlated with the progression of the pathology, although with controversial results. In addition, tumor necrosis factor α (TNFα) has been identified as an inflammatory biomarker strongly associated with AD, and several studies have consistently suggested the pharmacological targeting of TNFα to reduce systemic inflammation and prevent neurotoxicity in AD. Moreover, alterations in plasma metabolite levels appear to predict the progression of systemic processes relevant to brain functions. In this study, we analyzed the changes in the levels of Aβ42, TNFα, and plasma metabolites in subjects with AD and compared the results with those in healthy elderly (HE) subjects. Differences in plasma metabolites of patients with AD were analyzed with respect to Aβ42, TNFα, and the Mini-Mental State Examination (MMSE) score, searching for plasma signatures that changed simultaneously. In addition, the phosphorylation levels of the Tyr682 residue of the amyloid precursor protein (APP), which we previously proposed as a biomarker of AD, were measured in five HE and five AD patients, in whom the levels of Aβ42, TNFα, and two plasma lipid metabolites increased simultaneously. Overall, this study highlights the potential of combining different plasma signatures to define specific clinical phenotypes of patient subgroups, thus paving the way for the stratification of patients with AD and development of personalized approaches.

Impact of Truncated Oxidized Phosphatidylcholines on Phospholipase A2 Activity in Mono- and Polyunsaturated Biomimetic Vesicles

The interplay between inflammatory and redox processes is a ubiquitous and critical phenomenon in cell biology that involves numerous biological factors. Among them, secretory phospholipases A₂ (sPLA₂) that catalyze the hydrolysis of the sn-2 ester bond of phospholipids are key players. They can interact or be modulated by the presence of truncated oxidized phosphatidylcholines (OxPCs) produced under oxidative stress from phosphatidylcholine (PC) species. The present study examined this important, but rarely considered, sPLA₂ modulation induced by the changes in biophysical properties of PC vesicles comprising various OxPC ratios in mono- or poly-unsaturated PCs. Being the most physiologically active OxPCs, 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine (PGPC) have been selected for our study. Using fluorescence spectroscopy methods, we compared the effect of OxPCs on the lipid order as well as sPLA₂ activity in large unilamellar vesicles (LUVs) made of the heteroacid PC, either monounsaturated [1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)], or polyunsaturated [1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PDPC)] at a physiological temperature. The effect of OxPCs on vesicle size was also assessed in both the mono- and polyunsaturated PC matrices. Results: OxPCs decrease the membrane lipid order of POPC and PDPC mixtures with PGPC inducing a much larger decrease in comparison with POVPC, indicative that the difference takes place at the glycerol level. Compared with POPC, PDPC was able to inhibit sPLA₂ activity showing a protective effect of PDPC against enzyme hydrolysis. Furthermore, sPLA₂ activity on its PC substrates was modulated by the OxPC membrane content. POVPC down-regulated sPLA₂ activity, suggesting anti-inflammatory properties of this truncated oxidized lipid. Interestingly, PGPC had a dual and opposite effect, either inhibitory or enhancing on sPLA₂ activity, depending on the protocol of lipid mixing. This difference may result from the chemical properties of the shortened sn-2-acyl chain residues (aldehyde group for POVPC, and carboxyl for PGPC), being, respectively, zwitterionic or anionic under hydration at physiological conditions.

Alternative Targets for sPLA2 Activity: Role of Membrane-Enzyme Interactions

The secreted phospholipases A2 (sPLA2s) play important roles both physiologically and pathologically, with their expression increasing significantly in diseases such as sepsis, inflammation, different cancers, glaucoma, obesity, Alzheimer's disease and even COVID-19. The fact has led to a large-scale search for inhibitors of these enzymes. In total, several dozen promising molecules have been proposed, but not a single one has successfully passed clinical trials. The failures in clinical studies motivated in-depth fundamental studies of PLA2s. Here we review alternative ways to control sPLA2 activity, outside its catalytic site. The concept can be realized by preventing sPLA2 from attaching to the membrane surface; by binding to an external protein which blocks sPLA2 hydrolytic activity; by preventing sPLA2 from orienting properly on the membrane surface; and by preventing substrate binding to the enzyme, keeping the catalytic site unaltered. Evidence in the literature is summarized in the review with the aim to serve as a starting point for new types of sPLA2 inhibitors.

sPLA2 Wobbles on the Lipid Bilayer between Three Positions, Each Involved in the Hydrolysis Process

Secreted phospholipases A2 (sPLA2s) are peripheral membrane enzymes that hydrolyze phospholipids in the sn-2 position. The action of sPLA2 is associated with the work of two active sites. One, the interface binding site (IBS), is needed to bind the enzyme to the membrane surface. The other one, the catalytic site, is needed to hydrolyze the substrate. The interplay between sites, how the substrate protrudes to, and how the hydrolysis products release from, the catalytic site remains in the focus of investigations. Here, we report that bee venom PLA2 has two additional interface binding modes and enzyme activity through constant switching between three different orientations (modes of binding), only one of which is responsible for substrate uptake from the bilayer. The finding was obtained independently using atomic force microscopy and molecular dynamics. Switching between modes has biological significance: modes are steps of the enzyme moving along the membrane, product release in biological milieu, and enzyme desorption from the bilayer surface.

Singlet-Oxygen-Induced Phospholipase A2 Inhibition: A Major Role for Interfacial Tryptophan Dioxidation

Several studies have revealed that various diseases such as cancer have been associated with elevated phospholipase A2 (PLA2 ) activity. Therefore, the regulation of PLA2 catalytic activity is undoubtedly vital. In this study, effective inactivation of PLA2 due to reactive species produced from cold physical plasma as a source to model oxidative stress is reported. We found singlet oxygen to be the most relevant active agent in PLA2 inhibition. A more detailed analysis of the plasma-treated PLA2 identified tryptophan 128 as a hot spot, rich in double oxidation. The significant dioxidation of this interfacial tryptophan resulted in an N-formylkynurenine product via the oxidative opening of the tryptophan indole ring. Molecular dynamics simulation indicated that the efficient interactions between the tryptophan residue and phospholipids are eliminated following tryptophan dioxidation. As interfacial tryptophan residues are predominantly involved in the attaching of membrane enzymes to the bilayers, tryptophan dioxidation and indole ring opening leads to the loss of essential interactions for enzyme binding and, consequently, enzyme inactivation.

Spotlight on the protein corona of liposomes

Although an established drug delivery platform, liposomes have not fulfilled their true potential. In the body, interactions of liposomes are mediated by the layer of plasma proteins adsorbed on the surface, the protein corona. The review aims to collect the data of the last decade on liposome protein corona, tracing the path from interactions of individual proteins to the effects mediated by the protein corona in vivo. It offers a classification of the approaches to exploitation of the protein corona-rather than elimination thereof-based on the bilayer composition-corona composition-molecular interactions-biological performance framework. The multitude of factors that affect each level of this relationship urge to the widest implementation of bioinformatics tools to predict the most effective liposome compositions relying on the data on protein corona. Supplementing the picture with new pieces of accurately reported experimental data will contribute to the accuracy and efficiency of the predictions. STATEMENT OF SIGNIFICANCE: The review focuses on liposomes as an established nanomedicine platform and analyzes the available data on how the protein corona formed on liposome surface in biological fluids affects performance of the liposomes. The review offers a rigorous account of existing literature and critical analysis of methodology currently applied to the assessment of liposome-plasma protein interactions. It introduces a classification of the approaches to exploitation of the protein corona and tailoring liposome carriers to advance the field of nanoparticulate drug delivery systems for the benefit of patients.

Estimation of the Phospholipase A2 Selectivity on POPC/POPG Membranes Using the Interaction Map

Abstract

The regulation of the activity and selectivity of phospholipase A2 (PLA2), which is capable of cleaving fatty acid in the second position (sn-2) of the phospholipid, is carried out through the membrane-binding and catalytic sites of the enzyme. For hydrolytic activity, PLA2 must first bind to the phospholipid membrane, and the binding efficiency depends on the composition of the membrane. The membrane-binding site of PLA2 is formed by several tens of amino acids and its composition differs from enzyme to enzyme; hydrophobic and positively charged amino acids play a key role in the interaction. In this work, we investigated the interaction of PLA2 from bee venom with phospholipid bilayers of palmitoyl oleoylphosphatidylcholine (POPC) containing different amounts of palmitoyloleoylphosphatidylglycerol (POPG). On the basis of the measurements of the protein intrinsic fluorescence and the anisotropy of the fluorescence of the lipid probe we propose the construction of lipid–protein interaction maps, which reflect both the efficiency of protein binding and changes in the structure of the membrane. These changes cause alterations in the fluorescence anisotropy of the label, which in turn is a measure of the mobility of the lipid environment of the fluorescent probe. Analysis of interaction maps showed that there is a relationship between lipid mobility and enzyme binding efficiency: the optimum interaction of PLA2 with membranes from a POPC/POPG mixture lies in the region of the highest lipid mobility, and not in the region of the highest negative charge. This dependence complements the existing understanding of the process of recognition of the membrane surface by the enzyme and the selection of lipids by the enzyme already bound to the membrane. The proposed mapping method can be extended to other membrane-active proteins.