Molecular Assembly of Zinc Chlorophyll Derivatives by Using Recombinant Light-Harvesting Polypeptides with His-tag and Immobilization on a Gold Electrode

LH1-alpha and -beta polypeptides, which make up the light-harvesting 1 (LH1) complex of purple photosynthetic bacteria, along with bacteriochlorophylls, have unique binding properties even for various porphyrin analogs. Herein, we used the porphyrin analogs, Zn-Chlorin and the Zn-Chlorin dimer, and examined their binding behaviors to the LH1-alpha variant, which has a His-tag at the C-terminus (MBP-rub alpha-YH). Zn-Chlorin and the Zn-Chlorin dimer could bind to MBP-rub alpha-YH and form a subunit-type assembly, similar to that from the native LH1 complex. These complexes could be immobilized onto Ni-nitrilotriacetic acid modified Au electrodes, and the cathodic photocurrent was successfully observed by photoirradiation. Since Zn-Chlorins in this complex are too far for direct electron transfer from the electrode, a contribution of polypeptide backbone for efficient electron transfer was implied. These findings not only show interesting properties of LH1-alpha polypeptides but also suggest a clue to construct artificial photosynthesis systems using these peptide materials.