Molecular Assembly of Bacteriochlorophyll Complexes Using Synthetic Light-Harvesting Model Polypeptides

Abstract

Summary Molecular assembly of bacteriochlorophyll a (BChl a) or zinc-substituted bacteriochlorophyll a ([Zn]-BChl a) into an artificial antenna complex using synthetic light-harvesting (LH) model polypeptides has been achieved. Synthetic 1α-helix hydrophobic polypeptides, which have similar amino acid sequences to the hydrophobic core in the native LH-β polypeptide from Rba. sphaeroides, formed a BChl a complex in n-octyl-β-D-glucopyranoside (OG) micelles, analogous to the light-harvesting polypeptide complex of photosynthetic bacteria: this process is dependent on temperature and the polar amino acid sequences in the C-terminal segment. The minimum amino acid sequence in the N-terminal segment of the light-harvesting polypeptides of photosynthetic bacteria necessary for LH1-type complex-formation was that of type 2 of our synthetic hydrophobic polypeptides. A stable BChl a complex with a 2α-helix polypeptide, possessing disulfide linkage, was obtained in lipid bilayers and in OG micelles, analogous to the subunit complex, B820, of the LH 1 complex of photosynthetic bacteria. Further, the water-soluble synthetic 4α-helix polypeptide, HAHA formed a complex with BChl a and its analogues, similar to the LH1-type complex. Appropriate analogues of HAHA are also useful in providing an insight into the effect of polypeptide structure on LH complex formation and also for construction of an artificial LH complex.