PMID:15740753

Citation	Wang, ZY, Gokan, K, Kobayashi, M and Nozawa, T (2005) Solution structures of the core light-harvesting alpha and beta polypeptides from Rhodospirillum rubrum: implications for the pigment-protein and protein-protein interactions. J. Mol. Biol. 347:465-77
Abstract	We have determined the solution structures of the core light-harvesting (LH1) alpha and beta-polypeptides from wild-type purple photosynthetic bacterium Rhodospirillum rubrum using multidimensional NMR spectroscopy. The two polypeptides form stable alpha helices in organic solution. The structure of alpha-polypeptide consists of a long helix of 32 amino acid residues over the central transmembrane domain and a short helical segment at the N terminus that is followed by a three-residue loop. Pigment-coordinating histidine residue (His29) in the alpha-polypeptide is located near the middle of the central helix. The structure of beta-polypeptide shows a single helix of 32 amino acid residues in the membrane-spanning region with the pigment-coordinating histidine residue (His38) at a position close to the C-terminal end of the helix. Strong hydrogen bonds have been identified for the backbone amide protons over the central helical regions, indicating a rigid property of the two polypeptides. The overall structures of the R.rubrum LH1 alpha and beta-polypeptides are different from those previously reported for the LH1 beta-polypeptide of Rhodobacter sphaeroides, but are very similar to the structures of the corresponding LH2 alpha and beta-polypeptides determined by X-ray crystallography. A model constructed for the structural subunit (B820) of LH1 complex using the solution structures reveals several important features on the interactions between the LH1 alpha and beta-polypeptides. The significance of the N-terminal regions of the two polypeptides for stabilizing both B820 and LH1 complexes, as clarified by many experiments, may be attributed to the interactions between the short N-terminal helix (Trp2-Gln6) of alpha-polypeptide and a GxxxG motif in the beta-polypeptide.
Links	PubMed Online version:10.1016/j.jmb.2005.01.017
Keywords	Amino Acid Sequence; Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Circular Dichroism; Light-Harvesting Protein Complexes/chemistry; Light-Harvesting Protein Complexes/genetics; Light-Harvesting Protein Complexes/metabolism; Models, Molecular; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Protein Structure, Secondary; Protein Structure, Tertiary; Protein Subunits/chemistry; Protein Subunits/genetics; Protein Subunits/metabolism; Rhodospirillum rubrum/chemistry
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