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New Insights into the Protein Import Machinery of the Chloroplast's Outer Envelope
Author(s) -
Soll J.
Publication year - 1995
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1995.tb00495.x
Subject(s) - biology , gtpase , microbiology and biotechnology , phosphorylation , dephosphorylation , chromosomal translocation , gtp' , cytosol , organelle , biochemistry , translocon , transport protein , cytoplasm , phosphatase , gene , enzyme
A large number of plastid localized proteins are post‐translationally imported as precursor proteins from the cytosol into the organelle. Recognition and translocation is accomplished by a subset of chloroplast envelope proteins, which were identified by different but complementary methods. The o uter e nvelope p roteins OEP 86, OEP 75, OEP 70 (a heat shock cognate 70 homologue) and OEP 34 are clearly involved in the import event and can be isolated as one functionally active translocation unit. For three of these proteins cDNA clones have been very recently obtained, namely OEP 86, OEP 75 and OEP 34. OEP 86 seems to be a precursor protein receptor which could be regulated by GTP binding and ATP‐dependent phosphorylation‐dephosphorylation. OEP 75 is part of the translocation pore traversing the membrane in multiple β‐sheets. OEP 34 is tightly associated with OEP 75. It represents a new type of GTP‐binding protein which possesses endogenous GTPase activity. Multiple GTP binding and hydrolysis cycles as well as protein phosphorylation‐dephosphorylation events might, therefore, regulate the interaction of a precursor protein with the translocation machinery of the outer envelope, making it very distinct from the mitochondrial outer membrane system. Further proteins of the inner envelope membrane, namely IEP 97 and IEP 36, have been implied to function in the translocation event. These recent data allow not only identification of the players in the game but also speculation about mechanisms and regulation of translocation.