Determination of catabolism of the photosystem II D 1 subunit by structural motifs in the polypeptide sequence.

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 D 1 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 D 1 and its fragments with polyclonal antibodies. Antibodies against D 1 were found to react with other animal and plant proteins which contain similar sequence motifs.