Determination of Catabolism of the Photosystem II D 1 Subunit by Structural Motifs in the Polypeptide Sequence

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Abstract
Proteolytic mapping of the D 1 subunit of photosystem two and a degradation product which arises during its rapid catabolism shows that the latter is a result of proteolysis within the peptide motif QEEET. This motif is located in a portion of the D1 protein thought to form a stroma-exposed connection between fourth and fifth transmembrane segments. This connection domain also contains a “PEST”-like sequence and forms part of the QB/herbicide binding niche. The QEEET motif seems to provide a major epitope in immunological studies, as judged from reaction of D1 and its fragments with polyclonal antibodies. Antibodies against D1 were found to react with other animal and plant proteins which contain similar sequence motifs.