A SecY homologue is involved in chloroplast-encoded D1 protein biogenesis.
We have used the photosystem II reaction center D1 protein as a model to study the mechanisms of targeting and insertion of chloroplast-encoded thylakoid membrane proteins. The unusually high turnover rate and distinct pausing intermediates during translation make the D1 protein biogenesis particularly suitable for these purposes. Here we show that cpSecY, a chloroplast homologue of bacterial essential translocon component SecY, interacts tightly with thylakoid membrane-bound ribosomes, suggesting its involvement in protein translocation and insertion. Co-immunoprecipitation and cross-linking experiments indicated that cpSecY resides in the vicinity of D1 elongation intermediates and provided evidence for a transient interaction of cpSecY with D1 elongation intermediates during the biogenesis of D1. After termination of translation, such interactions no longer existed. Our results indicate that, in addition to a well characterized role of cpSecY in posttranslational translocation of nuclear-encoded proteins, it seems to be also involved in cotranslational membrane protein translocation and insertion in chloroplasts.
Zhang
L
L
Department of Biology, University of Turku, FIN-20014 Turku, Finland.
Paakkarinen
V
V
Suorsa
M
M
Aro
E M
EM
D001426:Bacterial Proteins / Q000502:physiology*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis* / Q000235:genetics; D045332:Photosystem II Protein Complex; D014176:Protein Biosynthesis; D012270:Ribosomes / Q000378:metabolism; D000069816:SEC Translocation Channels; D018724:Spinacia oleracea
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli