The light-harvesting polypeptides of Rhodopseudomonas sphaeroides R-26.1. II. Conformational analyses by attenuated total reflection infrared spectroscopy and the possible molecular structure of the hydrophobic domain of the B 850 complex.
Attenuated total reflection infrared spectroscopy were used to study the conformation of the purified light-harvesting polypeptides from Rhodopseudomonas sphaeroides R-26.1. B 870-alpha and B 850-beta are characterised by a high content of alpha-helix; B 850-alpha and B 870-beta, in contrast, contain extensive antiparallel chain-pleated sheet structure. The beta-structure is likely to be an artifact of the isolation because B 850-alpha assumes a predominantly alpha-helical conformation in the intact antenna complex. It is concluded that lipid-protein interactions play a crucial role in the stabilisation of the "native" alpha-helical fold of B 850-alpha and thus in the stabilisation of the entire antenna-pigment-protein complex. The results obtained concerning the "in situ" conformation of B 850-alpha and B 850-beta were used, together with the known primary structures and data available from the literature, to construct a rough molecular model of the hydrophobic domain of the elementary unit of the B 850 complex.
D001426:Bacterial Proteins / Q000302:isolation & purification*; D055598:Chemical Phenomena; D002621:Chemistry; D008961:Models, Structural; D045322:Photosynthetic Reaction Center Complex Proteins; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000032:analysis*; D013055:Spectrophotometry, Infrared / Q000379:methods
D001426:Bacterial Proteins; D045322:Photosynthetic Reaction Center Complex Proteins