BSCI 20021: Basic Microbiology Study Notes

BSCI 20021: Basic Microbiology Study Notes

mRNA Vaccines

  • Overview of mRNA vaccines and their role in microbiology.

Fluid Mosaic Model

  • Described as the early membrane model introduced in 1972.
  • Replaced various competing models and provided a unified picture of membrane features.
  • Reference: Cartoon of lipid taken from review by D.M. Engelman, Nature 2005.

Refined Model of Biological Membranes

  • Based on 50+ years of research following the work of Singer and Nicolson.
  • Reference: D.M. Engelman, Nature 2005.

Basic Composition of Biological Membranes

  • Biological membranes are primarily composed of:
    • Approximately 70-80% glycerophospholipids (lipid content).
    • Key component: Phosphatidylcholine (PC).
    • A single biological membrane contains hundreds of different lipids.
    • Variability comes from different headgroups and acyl-chain compositions.
  • Structure:
    • Apolar acyl chain(s) and polar headgroup.

Lyotropic Phase Behavior of Glycerophospholipids

  • Glycerophospholipids exhibit rich lyotropic phase behavior, referred to as the "shape-structure model."
    • Lipids self-assemble in various types of assemblies when in solvents:
    • Bilayer: E.g., Phosphatidylcholine (PC), Phosphatidylserine (PS).
      • Structure: Cylindrical.
    • Hexagonal Phase: Cone-shaped structure (e.g., Phosphatidylethanolamine (PE), Diacylglycerol (DAG), Phosphatidic acid (PA)).
    • Micellar Phase: Spherical and inverted cone shapes (e.g., Lysophosphatidylcholine (LPC)).

Diversity of Membrane Lipids

  • Major classes of lipids include:
    • Glycerophospholipids (Area of focus by Dr. Kooijman).
    • Sphingolipids.
    • Sterols and linear isoprenoids.
    • Glycolipids.

Classes of (Glycero-)Phospholipids

  • Characteristics:
    • Composed of a diverse yet limited number of lipid headgroups.
    • Overall neutral or carry a negative charge.
    • Diversity also arises from differing hydrocarbon chains.
  • Points of interest:
    • There are no positively charged glycerophospholipids.
    • Hydrocarbon chains play a crucial role in determining molecular shape:
    • Saturated fatty acids: E.g., Palmitic acid.
    • Unsaturated fatty acids: E.g., Linoleic acid.
Specific Types of Glycerophospholipids
  • Phosphatidic acid: Net charge -2 at pH 7.
  • Phosphatidylethanolamine: Neutral charge.
  • Phosphatidylcholine: Neutral charge.
  • Phosphatidylserine: Net charge -1.
  • Phosphatidylglycerol: Net charge -1.
  • Phosphatidylinositol 4,5-bisphosphate: Charge -4.
  • Cardiolipin: Net charge -2.

Ionizable Lipid Structure and Theoretical pKas

  • Emphasis on cationic lipids utilized in siRNA delivery and development.
  • Noteworthy cationic lipids include:
    • MC3 [92]: pKa 9.4
    • Lipid 319 [68]: pKa 9.4
    • C12-200 [103]: pKa 5
    • Others include: 5A2-SC8, Moderna Lipids, Genevant, etc.
  • Example: Notable pKas of specific lipids
  • Highlighted important for mRNA delivery efficacy within cells.

Mechanism of Action for Cationic Lipids

  • Shape Structure Concept:
    • Cylindrical shape supports bilayer structure.
    • Cone shape tends to disrupt bilayer structure.
  • Disruption of endosomal/lysosomal membrane releases some mRNA into the cell.

Production Methods of Lipid Nanoparticles (LNPs)

  • LNPs are produced via a process termed Self-Assembly.
    • Lipids are dissolved in ethanol, mRNA in an aqueous solution.
    • During mixing, polarity increases, shifting pH from acidic to neutral:
    • Lipids in ethanol, mRNA in water, initial pH 5.5-6.5, resulting in neutral pH 7.4.

Microfluidic Mixing Techniques

  • If required, detail methods for mixing solutions:
    • Staggered herringbone mixer: Schematic illustration detailing methods.
    • T-junction mixing: Efficiency in solvent mixing.
    • Hydrodynamic mixing: Another technique illustrated for achieving effective mixing.

Importance of Continuous Monitoring of SARS-CoV-2

  • Noted that SARS-CoV-2 rapidly mutates with new strains appearing frequently.
  • Initial vaccines may provide decreased efficacy against emerging strains today.
  • Emphasis on CDC recommendations regarding genomic surveillance and ongoing monitoring of COVID-19 Vaccine Efficacy (VE).
  • Query: Beyond rapid mutation, what is another reason for the emergence of new strains?