Related Experiment Video

Updated: Jul 17, 2026

Production and Visualization of Bacterial Spheroplasts and Protoplasts to Characterize Antimicrobial Peptide Localization
10:13

Production and Visualization of Bacterial Spheroplasts and Protoplasts to Characterize Antimicrobial Peptide Localization

Published on: August 11, 2018

Gram-negative outer and inner membrane models: insertion of cyclic cationic lipopeptides

Adrià Clausell1, Maria Garcia-Subirats, Montserrat Pujol

  • 1Physical Chemistry Department and Institute of Nanoscience and Nanotechnology, University of Barcelona, Av. Joan XXIII s/n, 08028 Barcelona, Spain.

The Journal of Physical Chemistry. B
|January 19, 2007
PubMed

Insights

Polymyxin B (PxB) is a potent antibiotic against Gram-negative bacteria. This study identifies key structural features, including cationic amphipathicity, essential for PxB

Area of Science:

  • Microbiology
  • Biochemistry
  • Drug Discovery

Background:

  • Polymyxin B (PxB) is a critical antibiotic for treating Gram-negative bacterial infections.
  • Understanding PxB's mechanism of action is crucial for developing new antibiotics with improved therapeutic indexes.
  • PxB interacts with both the outer membrane (OM) and inner membrane (IM) of bacteria.

Purpose of the Study:

  • To elucidate the key structural features of Polymyxin B essential for its antibacterial activity.
  • To investigate the role of specific domains, such as the hydrophobic region and positive charges, in PxB's interaction with bacterial membranes.
  • To understand how PxB induces membrane disruption leading to bacterial cell death.

Main Methods:

  • Mimicking bacterial outer and inner membranes using lipopolysaccharide (LPS) and anionic lipid (POPG) monolayers.
  • Utilizing penetration assays, pressure/area curve analysis, and Brewster angle microscopy to study peptide-membrane interactions.
  • Assessing peptide-induced membrane-membrane lipid exchange using phospholipid unilamellar vesicles.

Main Results:

  • Synthetic analogues confirmed the importance of the hydrophobic domain for LPS binding and the role of positive charges in membrane insertion.
  • The N-terminal acyl chain is crucial for high-affinity LPS interaction, while its absence prevents inner membrane insertion.
  • Cationic amphipathicity was identified as the primary determinant of PxB's antimicrobial activity, driving membrane disruption and lipid exchange.

Conclusions:

  • Specific structural elements of Polymyxin B dictate its interaction with bacterial membranes.
  • Cationic amphipathicity is the key driver of PxB's membrane-disrupting mechanism of action.
  • These findings provide a basis for designing novel PxB-based antibiotics with enhanced efficacy.

More Related Videos

Separation of the Cell Envelope for Gram-negative Bacteria into Inner and Outer Membrane Fractions with Technical Adjustments for Acinetobacter baumannii10:24

Separation of the Cell Envelope for Gram-negative Bacteria into Inner and Outer Membrane Fractions with Technical Adjustments for Acinetobacter baumannii

Published on: April 10, 2020

From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins09:55

From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins

Published on: July 4, 2016

Related Concept Videos

Formation of Lipopolysaccharides01:19

Formation of Lipopolysaccharides

Lipopolysaccharides (LPS) are crucial components of the outer membrane of Gram-negative bacteria, serving both structural and functional roles. It contributes to membrane stability and protects bacteria from host immune responses. LPS is composed of three major regions—lipid A, a core oligosaccharide, and an O antigen. The biosynthesis and assembly of LPS involve a highly coordinated set of enzymatic reactions and transport mechanisms. Additionally, LPS is recognized as an endotoxin, triggering...
Inhibitors of Gram-positive Cell Wall Synthesis01:23

Inhibitors of Gram-positive Cell Wall Synthesis

Bacterial cell walls are typically rigid structures composed mainly of peptidoglycan, a mesh-like polymer that provides mechanical strength and maintains cell shape. The synthesis of peptidoglycan is a crucial process in bacterial growth and serves as a primary target for many antibiotics.Mechanism of Action of Beta-Lactam AntibioticsBeta-lactam antibiotics, such as penicillin, inhibit peptidoglycan synthesis in actively growing cells. These antibiotics share a characteristic four-membered...
Structure of Porins01:21

Structure of Porins

Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel precursors...
Gram-negative Bacterial Protein Secretion Systems01:17

Gram-negative Bacterial Protein Secretion Systems

Gram-negative bacteria utilize sophisticated protein secretion systems to transport proteins across their double-membrane envelope into the extracellular environment or host cells. Based on their mechanism of action, these systems are classified into one-step and two-step pathways.One-Step Secretion Systems (Types I, III, IV, and VI)One-step secretion systems bypass the periplasm entirely, forming a continuous channel that spans both the inner and outer membranes:Type I Secretion System (T1SS):...
Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
Peptidoglycan Synthesis01:28

Peptidoglycan Synthesis

Structure of PeptidoglycanPeptidoglycan is a vital structural component of the bacterial cell wall, providing mechanical strength and shape to the cell. It consists of repeating units of two sugars—N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)—linked by β-1,4 glycosidic bonds. These sugar chains are cross-linked by short peptide chains, forming a mesh-like polymer that surrounds the bacterial plasma membrane.Cytoplasmic Phase – Precursor SynthesisPeptidoglycan biosynthesis begins in...