Construction of artificial light-harvesting complex using light-harvesting polypeptide or its model synthetic polypeptides with zinc substituted bacteriochlorophyll a

Abstract

Molecular assemblies of zinc-substituted bacteriochloropyll a (Zn-BChl a ) using light-harvesting ( LH ) polypeptide separately isolated from photosynthetic bacteria, R. rubrum and its model synthetic polypeptides were examined in lipid bilayers as well as in n-Octyl-b-D-glucopyranoside (OG) micelle. The key to the assemby is of constructing an artificial LH complex in lipid bilayers as well as of providing insight into structural requirements for formation of the core LH complex (LH 1). UV-vis., CD, SAXS, and DLS data indicated that the LH- a polypeptide selectively organizeds Zn-BChl a complex in OG micelle rather than BChl a complex, analogous to the LH1-type complex, depending on the temperature. Comparing the amino acid sequence in the N- and C-terminal segments of the LH- a polypeptide and its model peptides on the complex-formation with Zn-BChl a or BChl a reveals that the amino acid residues from M to F in the N-terminal segment of the LH-a polypeptide essentially account for the difference in the complex-formation between Zn-BChl a and BChl a. Interestingly, self-assembly of an artificial LH complex using the LH- a polypeptide and its model polypeptides with Zn-BChl a was observed in lipid bilayers. This is the first report that the native LH- a alone and its model peptides organize an artificial LH complex using Zn-BChl a, analogous to the LH 1-type complex of photosynthetic bacteria.