A thylakoidal processing peptidase from the heterokont alga Heterosigma akashiwo |
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Authors: | Chaal Balbir K Ishida Ken-ichiro Green Beverley R |
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Institution: | (1) Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada;(2) Department of Biology, Kanazawa University, Kanazawa, 920-1192, Japan |
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Abstract: | Heterokont algae such as diatoms, brown seaweeds and the raphidophyte Heterosigma akashiwo acquired their chloroplasts via a secondary endosymbiosis involving a red algal endosymbiont and a eukaryote host, resulting in chloroplasts surrounded by four membranes rather than two. The precursor of a nuclear-encoded thylakoid lumen protein, PsbO, from Heterosigma has a presequence composed of a typical ER signal peptide followed by putative stromal and thylakoid targeting domains. A processing enzyme associated with Heterosigma thylakoids cleaved the presequence (with or without the ER signal sequence) in a single step, giving a product of the size of the mature protein. Its sensitivity to a penem inhibitor and insensitivity to other protease inhibitors suggest that it is a member of the Type I signal peptidase family. Furthermore the Heterosigma enzyme appeared to have similar substrate specificity to the pea thylakoidal processing peptidase. |
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Keywords: | Heterosigma akashiwo PsbO thylakoidal processing peptidase thylakoid targeting domain |
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