Hydrophobicity light-harvesting complex

On the basis ofthe primary-structure information discussed above, and the known, 1 1 stoichiometry of the a- and p-polypeptides, Zuber developed a model for the light-harvesting BChl-protein complexes, as shown in Fig. 4 (A). In this model the two polypeptides span the chromatophore membrane with their hydrophobic segments consisting of 20 amino acids located in the hydrocarbon-tail region of the lipid-bilayer membrane. The polar N- and C-termini are located on the cytoplasmic and periplasmic sides, respectively. The hydrophobic amino acids in this model are present as an a-helix, in accord with the finding of a high helical content by circular dichroism. ... 

The heterodimer of PSI-A and PSI-B binds a number of chlorophyll a antennae molecules. A comparison of the sequence information from different species demonstrates that the PSI-A and PSI-B polypeptides contain 38 and 32 conserved histidine residues, respectively. The major part of these histidines (52 residues) are positioned in the hydrophobic a-helices. Histidine residues have been implicated in the coordination of chlorophyll in light-harvesting antennae complexes (36). The number of conserved histidines in the heterodimer corresponds well to the experimental value of 60 chlorophyll a/P700 in the barley core complex (4). 

Theiler R and Zuber H. The light-harvesting polypeptides of Rhodopseudomonas sphaeroides R-26-1. II. Conformational analyses by attenuated total reflection infrared spectroscopy and possible molecular structure of the hydrophobic domain of the B850 complex. Hoppe-Seyler s Z. Physiol. Chem. 1984 365 721-729. 

Functional biomaterial surfaces have been created to change between being hydrophobic and hydrophilic, in response to external signals, such as differences in temperature, solvent environment, light, or electrical current. Temperature-sensitive poly(A/-isopropylacrylamide) (PNIPAm)-coated substrate is hydrophobic at a cell culture temperature of 37°C that favors cell adhesion and becomes hydrophilic at a lower temperature of 20°C, causing the detachment of cell sheets. These reversible responsive surfaces have been used to culture and harvest layers of endothelial, epithelial, lung, liver, cardiac, and kidney cells, and could eventually enable assembly of complex tissues and organs. 

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