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Ezeduru V, Shao ARQ, Venegas FA, McKay G, Rich J, Nguyen D, Thibodeaux CJ. Defining the Functional Properties of Cyclopropane Fatty Acid Synthase from Pseudomonas aeruginosa PAO1. J Biol Chem 2024:107618. [PMID: 39095026 DOI: 10.1016/j.jbc.2024.107618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2024] [Revised: 07/20/2024] [Accepted: 07/22/2024] [Indexed: 08/04/2024] Open
Abstract
Cyclopropane fatty acid synthases (CFAS) catalyze the conversion of unsaturated fatty acids to cyclopropane fatty acids (CFAs) within bacterial membranes. This modification alters the biophysical properties of membranes and has been correlated with virulence in several human pathogens. Despite the central role played by CFAS enzymes in regulating bacterial stress responses, the mechanistic properties of the CFAS enzyme family and the consequences of CFA biosynthesis remain largely uncharacterized in most bacteria. We report the first characterization of the CFAS enzyme from Pseudomonas aeruginosa (PA) - an opportunistic human pathogen with complex membrane biology that is frequently associated with antimicrobial resistance and high tolerance to various external stressors. We demonstrate that CFAs are produced by a single enzyme in PA and that cfas gene expression is upregulated during the transition to stationary phase and in response to oxidative stress. Analysis of PA lipid extracts reveal a massive increase in CFA production as PA cells enter stationary phase and help define the optimal membrane composition for in vitro assays. The purified PA-CFAS enzyme forms a stable homodimer and preferentially modifies phosphatidylglycerol lipid substrates and membranes with a higher content of unsaturated acyl chains. Bioinformatic analysis across bacterial phyla shows highly divergent amino acid sequences within the lipid binding domain of CFAS enzymes, perhaps suggesting distinct membrane binding properties among different orthologues. This work lays an important foundation for further characterization of CFAS in Pseudomonas aeruginosa and for examining the functional differences between CFAS enzymes from different bacteria.
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Affiliation(s)
| | | | | | - Geoffrey McKay
- Research Institute of the McGill University Health Center, McGill University
| | - Jacquelyn Rich
- Research Institute of the McGill University Health Center, McGill University; Department of Microbiology and Immunology, McGill University
| | - Dao Nguyen
- Research Institute of the McGill University Health Center, McGill University; Department of Microbiology and Immunology, McGill University; Department of Medicine, McGill University
| | - Christopher J Thibodeaux
- Department of Chemistry, McGill University; Centre de Recherche en Biologie Structurale, McGill University.
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Puelles JS, Ghorbani M, Tuck B, Machuca LL, Ackland ML, Chen F, Somers AE, Forsyth M. Effect of cetrimonium carrier micelles on bacterial membranes and extracellular DNA, an in silico study. Sci Rep 2023; 13:8041. [PMID: 37198168 DOI: 10.1038/s41598-023-32475-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Accepted: 03/28/2023] [Indexed: 05/19/2023] Open
Abstract
Microorganisms do not live as dispersed single cells but rather they form aggregates with extracellular polymeric substances at interfaces. Biofilms are considered efficient life forms because they shield bacteria from biocides and collect dilute nutrients. This is a big concern in industry since the microorganisms can colonize a wide range of surfaces, accelerating material deterioration, colonizing medical devices, contaminating ultrapure drinking water, increasing energy costs and creating focus of infection. Conventional biocides that target a specific component of the bacteria are not effective in the presence of biofilms. Efficient biofilm inhibitors are based on a multitarget approach interacting with the bacteria and the biofilm matrix. Their rationale design requires a thorough understanding of inhibitory mechanisms that are still largely lacking today. Herein we uncover via molecular modelling the inhibition mechanism of cetrimonium 4-OH cinnamate (CTA-4OHcinn). Simulations show that CTA-4OH micelles can disrupt symmetric and asymmetric bilayers, representative of inner and outer bacterial membranes, following three stages: adsorption, assimilation, and defect formation. The main driving force for micellar attack is electrostatic interactions. In addition to disrupting the bilayers, the micelles work as carriers facilitating the trapping of 4OH cinnamate anions within the bilayer upper leaflet and overcoming electrostatic repulsion. The micelles also interact with extracellular DNA (e-DNA), which is one of the main components of biofilms. It is observed that CTA-4OHcinn forms spherical micelles on the DNA backbone; which hinders their ability to pack. This is demonstrated by modelling the DNA along the hbb histone-like protein, showing that in the presence of CTA-4OHcinn, DNA does not pack properly around hbb. The abilities of CTA-4OHcinn to cause cell death through membrane disruption and to disperse a mature, multi-species biofilm are also confirmed experimentally.
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Affiliation(s)
| | - Mahdi Ghorbani
- Institute for Frontier Materials, Deakin University, Geelong, VIC, 3217, Australia
| | - Benjamin Tuck
- Curtin Corrosion Centre, WA School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, Kent Street, Bentley, WA, 6102, Australia
| | - Laura L Machuca
- Curtin Corrosion Centre, WA School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, Kent Street, Bentley, WA, 6102, Australia
| | - M Leigh Ackland
- ARC Centre of Excellence for Electromaterials Science (ACES), Deakin University, Burwood, 3125, Australia
- School of Life and Environmental Sciences, Deakin University, Burwood, Victoria, 3125, Australia
| | - Fangfang Chen
- Institute for Frontier Materials, Deakin University, Geelong, VIC, 3217, Australia.
- ARC Centre of Excellence for Electromaterials Science (ACES), Deakin University, Burwood, 3125, Australia.
| | - Anthony E Somers
- Institute for Frontier Materials, Deakin University, Geelong, VIC, 3217, Australia.
| | - Maria Forsyth
- Institute for Frontier Materials, Deakin University, Geelong, VIC, 3217, Australia.
- ARC Centre of Excellence for Electromaterials Science (ACES), Deakin University, Burwood, 3125, Australia.
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Abstract
AbstractThe complex composition of bacterial membranes has a significant impact on the understanding of pathogen function and their development towards antibiotic resistance. In addition to the inherent complexity and biosafety risks of studying biological pathogen membranes, the continual rise of antibiotic resistance and its significant economical and clinical consequences has motivated the development of numerous in vitro model membrane systems with tuneable compositions, geometries, and sizes. Approaches discussed in this review include liposomes, solid-supported bilayers, and computational simulations which have been used to explore various processes including drug-membrane interactions, lipid-protein interactions, host–pathogen interactions, and structure-induced bacterial pathogenesis. The advantages, limitations, and applicable analytical tools of all architectures are summarised with a perspective for future research efforts in architectural improvement and elucidation of resistance development strategies and membrane-targeting antibiotic mechanisms.
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Hsieh MK, Yu Y, Klauda JB. All-Atom Modeling of Complex Cellular Membranes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:3-17. [PMID: 34962814 DOI: 10.1021/acs.langmuir.1c02084] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Cell membranes are composed of a variety of lipids and proteins where they interact with each other to fulfill their roles. The first step in modeling these interactions in molecular simulations is to have reliable mimetics of the membrane's lipid environment. This Feature Article presents our recent efforts to model complex cellular membranes using all-atom force fields. A short review of the CHARMM36 (C36) lipid force field and its recent update to incorporate the long-range dispersion is presented. Key examples of model membranes mimicking various species and organelles are given. These include single-celled organisms such as bacteria (E. coli., chlamydia, and P. aeruginosa) and yeast (plasma membrane, endoplasmic reticulum, and trans-Golgi network) and more advanced ones such as plants (soybean and Arabidopsis thaliana) and mammals (ocular lens, stratum corneum, and peripheral nerve myelin). Leaflet asymmetry in composition has also been applied to some of these models. With the increased lipid diversity in the C36 lipid FF, these complex models can better reflect the structural, mechanical, and dynamic properties of realistic membranes and open an opportunity to study biological processes involving other molecules.
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Hsieh MK, Klauda JB. Leaflet Asymmetry Modeling in the Lipid Composition of Escherichia coli Cytoplasmic Membranes. J Phys Chem B 2021; 126:184-196. [PMID: 34962410 DOI: 10.1021/acs.jpcb.1c07332] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Lipid composition asymmetry between leaflets is important to cell function and plays a key role in the "positive inside" rule in transmembrane proteins. In this work, Escherichia coli inner plasma membrane models reflecting this asymmetry have been investigated at the early-log and stationary stages during the bacterial lifecycle using all-atom molecular dynamics simulations. The CHARMM36 lipid force field is used, and selected membrane properties are tested for variations between two leaflets and whole membranes. Our models include bacterial lipids with a cyclopropane moiety on the sn-2 acyl chain in the stationary membrane model. The PE/PG ratio for two leaflets reflects the "positive inside" rule of membrane proteins, set to 6.8 and 2.8 for the inner and outer leaflets of the two models, respectively. We are the first to model leaflet asymmetry in the lipid composition of E. coli cytoplasmic membranes and observe the effect on membrane properties in leaflets and whole membranes. Specifically, our results show that for the stationary phase bilayer, the surface area per lipid (SA/lipid) is larger, the thickness (2DC and DB) is smaller, the tilt angle is larger, the tilt modulus is smaller, and the deuterium order parameters (SCD) of sn-1 and sn-2 tails are lower, compared to the early-log stage. Moreover, the stationary stage bilayer has a positive spontaneous curvature, while the early-log stage has a near flat spontaneous curvature. For leaflet asymmetry, the inner leaflet has a larger SA/lipid, a smaller thickness, a smaller elastic tilt modulus (a larger tilt angle), and lower SCD, compared to the outer leaflet in both stages. Moreover, an asymmetric membrane involves a lipid tilt and a lateral extension, varying from a reference state of a pre-equilibrium membrane. This work encourages a more profound exploration of leaflet asymmetry in various other membrane models and how this might affect the structure and function of membrane-associated peptides and proteins.
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Affiliation(s)
- Min-Kang Hsieh
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Jeffery B Klauda
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States.,Biophysics Program, University of Maryland, College Park, Maryland 20742, United States
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Abstract
Molecular simulations of biological molecules require an accurate description of molecular interactions through a force field (FF). The focus of this Perspective is on all-atom lipid FFs. Recent additions to the CHARMM36 lipid FF continue to expand a researcher's ability to probe membrane structure and function with a wide variety of biologically important lipids. Currently, there is an effort to reduce the assumptions in all-atom lipid FFs. The inclusion of long-range dispersion interaction through particle-mesh Ewald is allowing for more accurate descriptions of lipid bilayer and monolayer properties without additional computational cost. Soon, simulations with lipid FFs will no longer depend on short-range cutoffs and will accurately represent long-range dispersion. This requires efficient FF parametrization with an automated approach due to FF complexity. In addition, polarizable FFs for lipids will be important for the next generation of simulations that accurately represent how molecule interactions respond to a varied environment.
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Yuan Y, Yu Y, Klauda JB. Simulations of Diabetic and Non-Diabetic Peripheral Nerve Myelin Lipid Bilayers. J Phys Chem B 2021; 125:6201-6213. [PMID: 34081470 DOI: 10.1021/acs.jpcb.1c01621] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The multilayered myelin sheath is a critical component of both central and peripheral nervous systems, forming a protective barrier against axonal damage and facilitating the movement of nervous impulses. It is primarily composed of cholesterol (CHL1), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), sphingomyelin (SM), and galactosylceramide (GalCer) lipids. For rat sciatic nerve myelin (part of the peripheral nervous system, PNS), it has been found that cholesterol and unsaturated fatty acid contents are significantly lower in diabetic than in non-diabetic conditions. In this study, lipid compositions from experimental data are used to create four model rat sciatic nerve myelin lipid bilayers: PI-containing (non-diabetic and diabetic) and PS-containing (non-diabetic and diabetic), which were then simulated using the all-atom CHARMM36 force field. Simulation results of diabetic membranes indicate less rigid, more laterally expansive, and thinner bilayers as well as potentially reduced interactions between GalCer on opposing myelin leaflets, supporting a direct role of the cholesterol content decrease in instigating myelin deterioration and diabetic peripheral neuropathy. Compared to PI-lipids, PS-lipids were found to cause higher inter-lipid spacing and decreased order within membranes as a result of their smaller headgroup size and higher inter-lipid hydrogen bonding potential, which allow them to more frequently reside deeper in the membrane plane and produce pushing effects on other lipids. GalCer deuterium order parameters and non-diabetic headgroup-to-headgroup bilayer thicknesses were compared to experimental data, exhibiting close alignment, supporting the future usage of these models to study the PNS myelin sheath.
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Affiliation(s)
- Yiding Yuan
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Yalun Yu
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Jeffery B Klauda
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States.,Biophysics Graduate Program, University of Maryland, College Park, Maryland 20742, United States
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Yu Y, Krämer A, Venable RM, Simmonett AC, MacKerell AD, Klauda JB, Pastor RW, Brooks BR. Semi-automated Optimization of the CHARMM36 Lipid Force Field to Include Explicit Treatment of Long-Range Dispersion. J Chem Theory Comput 2021; 17:1562-1580. [PMID: 33620214 PMCID: PMC8059446 DOI: 10.1021/acs.jctc.0c01326] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The development of the CHARMM lipid force field (FF) can be traced back to the early 1990s with its current version denoted CHARMM36 (C36). The parametrization of C36 utilized high-level quantum mechanical data and free energy calculations of model compounds before parameters were manually adjusted to yield agreement with experimental properties of lipid bilayers. While such manual fine-tuning of FF parameters is based on intuition and trial-and-error, automated methods can identify beneficial modifications of the parameters via their sensitivities and thereby guide the optimization process. This work introduces a semi-automated approach to reparametrize the CHARMM lipid FF with consistent inclusion of long-range dispersion through the Lennard-Jones particle-mesh Ewald (LJ-PME) approach. The optimization method is based on thermodynamic reweighting with regularization with respect to the C36 set. Two independent optimizations with different topology restrictions are presented. Targets of the optimizations are primarily liquid crystalline phase properties of lipid bilayers and the compression isotherm of monolayers. Pair correlation functions between water and lipid functional groups in aqueous solution are also included to address headgroup hydration. While the physics of the reweighting strategy itself is well-understood, applying it to heterogeneous, complex anisotropic systems poses additional challenges. These were overcome through careful selection of target properties and reweighting settings allowing for the successful incorporation of the explicit treatment of long-range dispersion, and we denote the newly optimized lipid force field as C36/LJ-PME. The current implementation of the optimization protocol will facilitate the future development of the CHARMM and related lipid force fields.
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Affiliation(s)
- Yalun Yu
- Biophysics Graduate Program, University of Maryland, College Park, Maryland 20742, United States
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Andreas Krämer
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Richard M Venable
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Andrew C Simmonett
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Alexander D MacKerell
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland 21201, United States
| | - Jeffery B Klauda
- Biophysics Graduate Program, University of Maryland, College Park, Maryland 20742, United States
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Bernard R Brooks
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
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