Reconstitution of core light-harvesting complexes of photosynthetic bacteria using chemically synthesized polypeptides. 1. Minimal requirements for subunit formation.

Described are the chemical synthesis, isolation, and characterization of each of three polypeptides whose amino acid sequences reproduce portions of the amino acid sequence of the β-polypeptides of the core light-harvesting complex (LH1) of Rhodobacter sphaeroides or Rhodospirillum rubrum. The native β-polypeptides of LH1 of these organisms contain 48 and 54 amino acids, respectively. The smallest synthetic polypeptide had an amino acid sequence identical to that of the last 16 amino acids of the β-polypeptide of Rb. sphaeroides (sphβ16) but failed to form either a subunit- or LH1-type complex under reconstitution conditions. Also, this polypeptide, lengthened on the N terminus by adding the sequence Lys-Ile-Ser-Lys to enhance solubility, failed to form a subunit- or LH1-type complex. In contrast, polypeptides containing either the 31 amino acids at the C terminus of the β-polypeptide of Rb. sphaeroides (sphβ31) or the equivalent 31 amino acids of the β-polypeptide of Rs. rubrum (rrβ31) were fully compete...