PIGMENT COMPLEXES OF LIGHT‐HARVESTING CHLOROPHYLL a/b BINDING PROTEIN ARE STABILIZED BY A SEGMENT IN THE CARBOXYTERMINAL HYDROPHILIC DOMAIN OF THE PROTEIN*

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Abstract
In order to identify segments of light‐harvesting chlorophyll a/6‐binding protein (LHCP) that are important for pigment binding, we have tested various LHCP mutants regarding their ability to form stable pigment‐protein complexes in an in vitro reconstitution assay. Deletion of 10 C‐terminal amino acids in the LHCP precursor, pLHCP, did not significantly affect pigment binding, whereas deletion of one additional amino acid, a tryptophan, completely abolished the formation of stable pigment‐protein complexes. This tryptophan, however, can be exchanged with other amino acids in full‐length pLHCP without noticeably altering the stability or spectroscopic properties of pigment complexes made with these mutants. Thus, the tryptophan residue is not likely to be involved in a highly specific interaction stabilizing the complex. A double mutant of LHCP lacking 66 N‐terminal and 6 C‐terminal amino acids still forms pigmented complexes that are virtually identical to those formed with the full‐length protein concerning their pigment composition and spectroscopic properties. We conclude that about 30% of the polypeptide chain in LHCP is not involved in pigment binding.