PARENT SESSION
Posters P3A Bacteriochlorophyll based antenna systems. Abstracts (219-238)

Self-assembly of hydrophobic fusion proteins with a photosynthetic pigment. Miku SUGIMOTO^*,1, Kiyotaka YOSHIDA¹, Takehisa DEWA¹, Keiji YAMASHITA¹, Mamoru NANGO¹, ¹ Materials Science and Engineering, Nagoya, Aichi, Japan

ABSTRACT- In a primary photosynthetic event, light-harvesting complexes, LH1 and LH2, capture and transfer solar energy to reaction center, where converts the light energy into electrochemical energy efficiently. The LH1 complex consists of pigments and LH- and- polypeptides. These components enable to self-assemble native-like complex in n-octyl--D-glucopyranoside (OG) micellar solution. To investigate such self-assembling properties is expected to provide useful information about the structural essence and the mechanism of energy transfer. We report herein self-assembling properties of a pigment with cysteine-bearing hydrophobic polypeptides analogous to the LH1 complex in a purple photosynthetic bacterium. To examine the influence of dimerization and oligomerization of the polypeptides via disulfide linkage upon self-assembling with a pigment, we designed four types of polypeptide, whose hydrophobic core sequence is conserved that of LH1 polypeptide of Rhodobacter sphaeroides, bearing cysteine(s) on the N- and / or C-terminal region(s). These polypeptides were obtained as water-soluble fusion proteins with maltose-binding protein (MBP) by using Escherichia coli expression system. The fusion proteins and zinc-substituted bacteriochlorophyll a (Zn-BChl a) were reconstituted in OG micellar solution. The reconstituted complex exhibited red-shifted Qy band characteristic of "subunit-type" complex. It is noteworthy that the fusion protein / pigment complexes enable to assemble despite of the steric confinements of both MBP portion (40kDa) and disulfide crosslinkage. By cleavage of the MBP part, the subunit complex further assembled to form "core-type" complex, judging from the further red-shifted Qy band and splitted CD signal.

KEY WORDS: bacteriochlorophyll a, model peptide, Self-assembly, reconstitution