Complete maturation of the plastid protein translocation channel requires a type I signal peptidase

• Published in: The Journal of cell biology Vol. 171; no. 3; pp. 425 - 430
• Main Authors: Inoue, Kentaro, Baldwin, Amy J, Shipman, Rebecca L, Matsui, Kyoko, Theg, Steven M, Ohme-Takagi, Masaru
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 07-11-2005; The Rockefeller University Press
• Subjects: Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Cell membranes; Cellular biology; Chloroplasts; Complementary DNA; Enzymes; Escherichia coli Proteins - genetics; Flowers & plants; Membrane Proteins - genetics; Membrane Proteins - metabolism; Nuclear Envelope - enzymology; Peptides; Plants; Plants, Genetically Modified; Plastids; Plastids - enzymology; Protein precursors; Protein Precursors - genetics; Protein Precursors - metabolism; Protein Processing, Post-Translational; Protein transport; Proteins; Seedlings; Seedlings - enzymology; Seedlings - genetics; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; Signal transduction; Thylakoids; Thylakoids - enzymology; Thylakoids - ultrastructure
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200506171

The protein translocation channel at the plastid outer envelope membrane, Toc75, is essential for the viability of plants from the embryonic stage. It is encoded in the nucleus and is synthesized with a bipartite transit peptide that is cleaved during maturation. Despite its important function, the molecular mechanism and the biological significance of the full maturation of Toc75 remain unclear. In this study, we show that a type I signal peptidase (SPase I) is responsible for this process. First, we demonstrate that a bacterial SPase I converted Toc75 precursor to its mature form in vitro. Next, we show that disruption of a gene encoding plastidic SPase I (Plsp1) resulted in the accumulation of immature forms of Toc75, severe reduction of plastid internal membrane development, and a seedling lethal phenotype. These phenotypes were rescued by the overexpression of Plsp1 complementary DNA. Plsp1 appeared to be targeted both to the envelope and to the thylakoidal membranes; thus, it may have multiple functions.