title: A thylakoidal processing peptidase from the heterokont alga Heterosigma akashiwo.
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.
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada.
authors.forename: Balbir K
authors.initials: BK
authors.lastname: Chaal
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Ishida
authors.forename: Beverley R
authors.initials: BR
authors.lastname: Green
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000235:genetics* / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D056890:Eukaryota / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000201:enzymology; D011498:Protein Precursors / Q000235:genetics; D021382:Protein Sorting Signals / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D020418:Algal Proteins; D004791:Enzyme Inhibitors; D011498:Protein Precursors; D021382:Protein Sorting Signals; D010450:Endopeptidases; C069654:thylakoid processing peptidase