Proteins in photosynthetic membranes URLanize into patterned arrays that span the membrane's lateral size. Attractions between proteins in different layers of a membrane stack can play a key role in this ordering, as was suggested by microscopy and fluorescence spectroscopy and demonstrated by computer simulations of a coarse-grained model. The architecture of thylakoid membranes, however, also provides opportunities for inter-layer interactions that instead disfavor the high protein densities of ordered arrangements. Here we explore the interplay between these opposing driving forces and in particular the phase transitions that emerge in the periodic geometry of stacked thylakoid membrane disks. We propose a lattice model that roughly accounts for proteins' attraction within a layer and across the stromal gap, steric repulsion across the lumen gap, and regulation of protein densityby exchange with the stroma lamellae  Mean field analysis and computer simulation reveal rich phase behavior for this simple model, featuring a broken-symmetry stripephase that is disrupted at both high and low extremes of chemical potential. The resulting sensitivity of microscopic protein arrangement to the thylakoid's mesoscale vertical structure raises intriguing possibilities for regulation of photosynthetic function.
Proteins in photosynthetic membranes URLanize into patterned arrays that span the membrane's lateral size. Attractions between proteins in different layers of a membrane stack can play a key role in this ordering, as was suggested by microscopy and fluorescence spectroscopy and demonstrated by computer simulations of a coarse-grained model. The architecture of thylakoid membranes, however, also provides opportunities for inter-layer interactions that instead disfavor the high protein densities of ordered arrangements. Here we explore the interplay between these opposing driving forces and in particular the phase transitions that emerge in the periodic geometry of stacked thylakoid membrane disks. We propose a lattice model that roughly accounts for proteins' attraction within a layer and across the stromal gap, steric repulsion across the lumen gap, and regulation of protein density by exchange with the stroma lamellae . Mean field analysis and computer simulation reveal rich phase behavior for this simple model, featuring a broken-symmetry stripe phase that is disrupted at both high and low extremes of chemical potential. The resulting sensitivity of microscopic protein arrangement to the thylakoid's mesoscale vertical structure raises intriguing possibilities for regulation of photosynthetic function.
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