Characterization of Protein-Membrane Interfaces through a Synergistic Computational-Experimental Approach

The characterization of biological interfaces is widely recognized as one of the main challenges for modern biology. In particular, biological membranes are nowadays known to be an active environment that allows membrane proteins to perform their work and modulates their function. Integral and peripheral membrane proteins constitute 1/3 of the human proteome, and account for about 50% of the targets of modern medicinal drugs. Despite their remarkable role, their interplay with the membrane is often poorly characterized, mainly because of the limits that the currently available experimental techniques encounter when treating hydrophobic environments. In particular, peripheral membrane proteins are often studied in their soluble version: this approach is highly limiting, as the interaction with the membrane is essential for the activity of these biomolecules. Here, we show the potential of a combined computational-experimental approach in order to overcome the aforementioned limits. In particular, we use molecular modeling to study two peripheral membrane proteins of interest, and successively design ad hoc wet lab experiments to verify the outcomes and predictions of the simulations. This approach allows to bypass the technical limits and high costs of the wet lab techniques, by guiding the experiments with the data of the computational simulations. We focused our attention on the following peripheral membrane proteins: New Delhi metallo-beta-lactamase (NDM-1). NDM-1 is a bacterial enzyme that causes antibiotic resistance. Within the class of metallo-beta-lactamases, it represents the most serious threat to global health. The larger resistance of NDM-1 with respect to other proteins of the same class, has been linked to its post-translational modification, which connects it to the outer bacterial membrane of Gram-negative bacteria: this event can significantly increase the chances of NDM-1 to spread through the infection through vesicles excretion. In the present work, we elucidated the mechanistic aspects of the NDM-1/bacterial membrane interaction, and identified the features that contribute to the efficiency of this mechanism. Golgi phosphorylated protein 3 (Golph3). Golph3 is a peripheral membrane protein present at the Golgi apparatus of most eukaryotic cells. Its normal function consists in binding glycosylating enzymes, and transport them through the Golgi cisternae. In humans, Golph3 has been found to be overexpressed in several forms of cancer: however, no Golph3 inhibitors are currently present in the pharmaceutical market. This is mainly due to the lack of structural information regarding the molecular mechanism of Golph3. Here, we clarify the features of Golph3 that allow it to bind to the Golgi, and elucidate the mechanism of membrane binding. We also propose a recognition mechanism between Golph3 and the glycoenzymes, based on events predicted by the computer simulations. Overall, in the present work we demonstrate the potential of computational-experimental approaches in structural biology, and in particular in the study of peripheral membrane proteins. We show that a combined approach constitutes the best way of overcoming the limits of each technique, and we discuss the repercussions on the study of systems of biological interest

Structure Based Modeling of Small Molecules Binding to the TLR7 by Atomistic Level Simulations

Toll-Like Receptors (TLR) are a large family of proteins involved in the immune system response. Both the activation and the inhibition of these receptors can have positive effects on several diseases, including viral pathologies and cancer, therefore prompting the development of new compounds. In order to provide new indications for the design of Toll-Like Receptor 7 (TLR7)-targeting drugs, the mechanism of interaction between the TLR7 and two important classes of agonists (imidazoquinoline and adenine derivatives) was investigated through docking and Molecular Dynamics simulations. To perform the computational analysis, a new model for the dimeric form of the receptors was necessary and therefore created. Qualitative and quantitative differences between agonists and inactive compounds were determined. The in silico results were compared with previous experimental observations and employed to define the ligand binding mechanism of TLR7

Molecular Bases of the Membrane Association Mechanism Potentiating Antibiotic Resistance by New Delhi Metallo-beta-lactamase 1

Resistance to last-resort carbapenem antibiotics is an increasing threat to human health, as it critically limits therapeutic options. Metallo-beta-lactamases (MBLs) are the largest family of carbapenemases, enzymes that inactivate these drugs. Among MBLs, New Delhi metallo-beta-lactamase 1 (NDM-1) has experienced the fastest and largest worldwide dissemination. This success has been attributed to the fact that NDM-1 is a lipidated protein anchored to the outer membrane of bacteria, while all other MBLs are soluble periplasmic enzymes. By means of a combined experimental and computational approach, we show that NDM-1 interacts with the surface of bacterial membranes in a stable, defined conformation, in which the active site is not occluded by the bilayer. Although the lipidation is required for a long-lasting interaction, the globular domain of NDM-1 is tuned to interact specifically with the outer bacterial membrane. In contrast, this affinity is not observed for VIM-2, a natively soluble MBL. Finally, we identify key residues involved in the membrane interaction with NDM-1, which constitute potential targets for developing therapeutic strategies able to combat resistance granted by this enzyme

Explaining the Microtubule Energy Balance: Contributions Due to Dipole Moments, Charges, van der Waals and Solvation Energy

Microtubules are the main components of mitotic spindles, and are the pillars of the cellular cytoskeleton. They perform most of their cellular functions by virtue of their unique dynamic instability processes which alternate between polymerization and depolymerization phases. This in turn is driven by a precise balance between attraction and repulsion forces between the constituents of microtubules (MTs)—tubulin dimers. Therefore, it is critically important to know what contributions result in a balance of the interaction energy among tubulin dimers that make up microtubules and what interactions may tip this balance toward or away from a stable polymerized state of tubulin. In this paper, we calculate the dipole–dipole interaction energy between tubulin dimers in a microtubule as part of the various contributions to the energy balance. We also compare the remaining contributions to the interaction energies between tubulin dimers and establish a balance between stabilizing and destabilizing components, including the van der Waals, electrostatic, and solvent-accessible surface area energies. The energy balance shows that the GTP-capped tip of the seam at the plus end of microtubules is stabilized only by − 9 kcal/mol, which can be completely reversed by the hydrolysis of a single GTP molecule, which releases + 14 kcal/mol and destabilizes the seam by an excess of + 5 kcal/mol. This triggers the breakdown of microtubules and initiates a disassembly phase which is aptly called a catastrophe

Explaining the microtubule energy balance: contributions due to dipole moments, charges, van der Waals and solvation energy

Microtubules are the main components of mitotic spindles, and are the pillars of the cellular cytoskeleton. They perform most of their cellular functions by virtue of their unique dynamic instability processes which alternate between polymerization and depolymerization phases. This in turn is driven by a precise balance between attraction and repulsion forces between the constituents of microtubules (MTs)—tubulin dimers. Therefore, it is critically important to know what contributions result in a balance of the interaction energy among tubulin dimers that make up microtubules and what interactions may tip this balance toward or away from a stable polymerized state of tubulin. In this paper, we calculate the dipole–dipole interaction energy between tubulin dimers in a microtubule as part of the various contributions to the energy balance. We also compare the remaining contributions to the interaction energies between tubulin dimers and establish a balance between stabilizing and destabilizing components, including the van der Waals, electrostatic, and solvent-accessible surface area energies. The energy balance shows that the GTP-capped tip of the seam at the plus end of microtubules is stabilized only by −9 kcal/mol, which can be completely reversed by the hydrolysis of a single GTP molecule, which releases +14 kcal/mol and destabilizes the seam by an excess of +5 kcal/mol. This triggers the breakdown of microtubules and initiates a disassembly phase which is aptly called a catastrophe

Insights in the recognition of Listeria cell wall teichoic acids by a phage-derived cell wall binding module

SEBBM19madrid, Madrid on 16-19th July 2019, G05-13-P7 f. -- https://congresosebbm.madrid2019.es/Endolysins are phage-encoded peptidoglycan hydrolases able to degrade the cell-wall of bacterial hosts from the inside and the outside. Often they are modular enzymes bearing separate recognition and catalytic functions. Susceptibility to lytic activity depends on the selectivity of their cell wall-binding domain (CBD) frequently a carbohydrate-recognition domain. As significant example the CBD of the phage endolysin Ply500 (CBD500) exhibits binding patterns that correlate with structural variations in wall teichoic acids (WTAs) of Listeria spp. their target bacteria [1]. Yet atomic scale insights in this interaction remain challenging to obtain due to the extraordinary heterogeneity of these glycopolymers in terms of length GlcNAc/ribitol connectivity mutable O-acetylation or further hexose substitution of the GlcNAc unit. In this work we employed a multifaceted strategy in order to decipher the CBD500 fine sugar specificity and WTA recognition mechanism from both the ligand and protein perspectives. Saturation Transfer Difference (STD) NMR of CBD500-complexes with a panel of native and mutant WTAs highlighted the importance of GlcNAc 3¿O-acetylation and the relevant contributions of hexose substitutions in binding. ¿Blind¿ molecular docking on the X-ray structure of CBD500 allowed us to propose the WTA binding site and the putative interacting groups further assessed by site-directed mutagenesis. STD NMR-driven molecular dynamic simulations and isothermal titration calorimetry (ITC) aided to model the CBD500 interaction with targeted WTA and analyze the H-bond network as well as hydrophobic interactions established. This pioneer study unveiled the previously unknown recognition mechanism between CBD500 and Listeria native WTA polymers thus guiding further studies aiming to decipher the regulation of endolysin specificity