#polyethylene glycol

Plant tissue culture 2

Which of the following is NOT a fusogen?

Colchicine is not considered fusogen, unlike true fusogenic agents that promote membrane merging of protoplasts. Legitimate fusogens include polyethylene glycol PEG high molecular weight polymer that dehydrates membrane interface creating calcium bridges neutralizing negative charge inducing lipid mixing upon dilution, high concentration calcium ions at alkaline pH around 10.5 similar mechanism reducing electrostatic repulsion, and inactivated Sendai virus bearing fusogenic HN and F glycoproteins that merge animal and plant membranes albeit rarely used now due to biohazard handling. Electrical pulses via electrofusion also physically fuse membranes through reversible dielectric breakdown not chemical fusogen definition but effective. Colchicine mechanism distinct: it binds tubulin dimer with high affinity blocking microtubule assembly disrupting spindle formation during mitosis leading to polyploidy chromosome doubling, classified as antimitotic alkaloid rather than membrane fusogen. It does not destabilize lipid bilayer nor create intermembrane coalescence step necessary for protoplast fusion. Hence in lists evaluating fusogenic compounds colchicine stands out as non fusogenic used for ploidy manipulation rather than heterokaryon formation, correctly identified as answer for which is NOT fusogen.

Ref: Anne & Harada 1991 fusogens list; Kao 1977 colchicine not fusogen.

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Plant tissue culture 2

Common fusogen used for induced protoplast fusion is:

Common chemical fusogen employed to induce protoplast fusion is polyethylene glycol PEG polymer with molecular weight typically 1500 to 6000 daltons applied at concentration 15 to 40 percent weight per volume combined with calcium ions 50 millimolar and alkaline pH 9 to 10. PEG induces fusion through multiple mechanisms: it is highly hydrophilic binding water molecules dehydrating intermembrane space reducing hydration repulsion between negatively charged phospholipid bilayers, promotes close apposition of membranes via calcium bridging between phosphate head groups and creates molecular disorder increasing membrane fluidity and probability of lipid mixing and coalescence upon gradual dilution washing out PEG. Efficiency of heterokaryon formation ranges 10 to 30 percent depending on species and concentration exposure time 15 to 30 minutes. Although PEG causes some cytotoxicity protein denaturation requiring thorough washing after treatment, it remains cheapest most accessible method for somatic hybridization compared to electrofusion equipment requiring electroporators. Other chemical fusogens include high calcium alkaline pH alone and inactivated Sendai virus with fusogenic hemagglutinin proteins. PEG fusion nonspecifically generates multinucleate products but selection via fluorescence markers or complementation enables recovery of desired hybrids for crop improvement.

Ref: Kao & Michayluk 1974 PEG fusion; NCBI protoplast fusion review.

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Immunological Applications

PEG (polyethylene glycol) is used in hybridoma technology for:

Efficient cell fusion must overcome hydration repulsion keeping lipid bilayers approximately two nanometers apart due to ordered water molecules bound to phosphatidylcholine headgroups. Polyethylene glycol with molecular weight 1450 to 4000 daltons is extremely hygroscopic linear polymer containing repeating ether oxygens that strongly bind water through hydrogen bonding, lowering water activity dramatically and creating osmotic stress that forces membranes into close proximity below one nanometer. At concentrated 40 to 50 percent weight per volume, PEG disrupts lipid packing, induces inverted hexagonal phase propensity, promotes hemifusion stalk formation between apposed outer leaflets as demonstrated by electron microscopy, then upon rapid dilution with serum-free medium stalk expands into fusion pore allowing mixing of cytoplasm, mitochondria, and endoplasmic reticulum. Unlike electrofusion requiring specialized cuvettes delivering kilovolt pulses or Sendai virus envelope hemagglutinin-neuraminidase introducing viral antigens that provoke immune response and hinder clinical use, PEG is chemically inert, inexpensive, and easily washed after one minute exposure. Cytotoxicity minimized by controlled exposure timing. Yield typically one stable hybrid per ten thousand B cells, sufficient selection amplifies later.

Ref: Lentz J Mol Biol PEG fusion membrane dehydration; Alberts MBoC membrane fusion hemifusion stalk; Nature Protocols PEG hybridoma.

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Immunological Applications

PEG (polyethylene glycol) is used in hybridoma technology for:

Polyethylene glycol polymer repeating ethylene oxide units average MW 1500 Da widely employed fusogen hybridoma generation due unique physicochemical properties affecting membrane biophysics. Mechanism involves strong hygroscopic nature binding water around phospholipid headgroups phosphatidylcholine sphingomyelin reducing hydration repulsion normally maintaining 2-3 nm separation bilayers enabling close apposition

Ref: Kohler Milstein PEG Fusion Method 1976 Detailed; Alberts Membrane Fusion PEG Mechanism Biophysical; Janeway Hybridoma PEG Fusion Laboratory Protocol Chapter 5.

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