Hexagonal H-II inverted cylindrical phase of lipids does not obviously fit with fluid mosaic lipid bilayer structure of biological membranes; yet MGDG in thylakoid membranes dominates - how?
Article Magnetic resonance studies of dynamic organisation of lipids...
Thanks Pavel, in a mixture of lipids that constitute chloroplast thylakoid membranes: about 40 percent are H-II phase forming MGDG. Rest are bilayer-lamellar phase forming DGDG (25%), phospholipids (10%) and sulpholipid (5%). Together with pigments (chlorophyll and caratenoids), the mixture forms fairly stable lipid bilayers.
I personally suspect that the high content of transmembrane helices in the thylakoid membrane might be an important factor to stabilize the bilayer. The exact (more or less) lipid composition is present in the prolamellar body (PLB) which forms in etioplasts and in this is characterized by a cubic phase. On the other hand, the very high content of protochlorophyllide-protochlorophyllide reductase complexes might play a role in maintaining the cubic structure of the PLB. Soon after illumination which induces transformation of the protochlorophyllide to chlorophyllide the PLB "dissolves" and lamellar structures start to form. The attached paper seems like a great source of new information on this topic. I will read it and possibly revise my opinion.
http://www.fasebj.org/content/early/2014/04/16/fj.13-247395.abstract
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