Fluid mosaic model of membranes

Water-Ice Phase Transition

Membrane lipid adaptation to cold

• Main changes in fatty acyl composition

• Smaller changes in head group

Membrane lipid fatty acyl adaptation to cold

• more unsaturation

• more branching (anteiso and/or iso)

• shorter chain length

Membrane lipid fatty acyl adaptation to cold

• more unsaturation

• more branching (anteiso and/or iso)

• shorter chain length

Unsaturated fatty acids

Cis and trans unsaturated fatty acids

Liquid-crystalline Lipid Phase

Membrane lipid fatty acyl adaptation to cold

• more unsaturation

• more branching (anteiso and/or iso)

• shorter chain length

CH2 CH2 CH2 CH3

straight-chain

CH2 CH2 CH CH3

CH3

iso-branched

CH2 CH CH2 CH3

CH3

anteiso-branched

Fluidising effect : Anteiso > Iso > Straight

Methyl-branched fatty acids

Membrane lipid fatty acyl adaptation to cold

• more unsaturation

• more branching (anteiso and/or iso)

• shorter chain length

Liquid-crystallineto gel phasetransition

Liquid-crystalline

Phase Gel Phase

Liquid-crystallineto gel phasetransition

Lipid fluidity influences membrane proton permeability

Homeo-proton Permeability Adaptation

Decreasedtemperature

Liquid-crystallineto gel phasetransition

Bilayer (lamellar) to non-bilayer

(e.g. hexagonal) phasetransition

Homeoviscous adaptation Homeophasic adaptation

Bilayer (lamellar) to non-bilayer

(e.g. hexagonal) phasetransition

Antarctica Dry Valleys (Taylor Valley)

Bilayer (lamellar) phase

Phosphatidylglyerol

Non-bilayer hexagonal phase

Unsaturated Phosphatidylethanolamine

Decreasedtemperature

Altered lipid fatty acyl composition

Altered lipid head group composition

Homeophasic adaptation

Decreasedtemperature

• Increase inunsaturation

• Increase in cis/trans ratio

• Changes in methyl branching

• Shortening of acylchain length

Rapid Slow

Precursors

Intermediate

Saturated Monounsaturated FA FA

Anaerobic pathway Aerobic pathway

Precursors

FAS

SFA

Desaturase

UFA

Bacterial unsaturated fatty acid biosynthesis

Acetyl-ACP

ß-Hydroxy-decanoyl-ACP

Trans-2-decenoyl-ACP Cis-3-decenoyl-ACP

16:0 16:1Δ9

18:0 18:1Δ11

Saturated Unsaturated

Anaerobic pathway

Cellular organisation of unsaturatedfatty acid and membranephospholipid biosynthesis

Cell membrane – Lipid bilayer

UFA-PL SFA-PL

Precursors Anaerobic

pathway FAS

UFA SFA

Phospholipid biosynthesis

Desaturase

Importance of hydrophobic α-helices in protein-lipid interactions

Integral Membrane Protein