Chloroplast Oxa1p Homolog Albino3 Is Required for Post-translational Integration of the Light Harvesting Chlorophyll-binding Protein into Thylakoid Membranes

• Published in: The Journal of biological chemistry 2000-01, Vol.275 (3), p.1529-1532
• Main Authors: Moore, Misty, Harrison, M.Stephen, Peterson, Eric C., Henry, Ralph
• Format: Article
• Language: English
• Subjects: antibodies; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins; Arabidopsis thaliana; binding; binding proteins; Biological Transport; Chloroplasts - metabolism; Electron Transport Complex IV - metabolism; immunoglobulin G; Immunoglobulin G - pharmacology; inhibition; Intracellular Membranes - metabolism; light harvesting complex; Light-Harvesting Protein Complexes; Mitochondrial Proteins; Nuclear Proteins - physiology; Photosynthetic Reaction Center Complex Proteins - metabolism; Plant Proteins - genetics; Plant Proteins - physiology; Plasmids - metabolism; Protein Binding; Protein Processing, Post-Translational; protein transport; Reverse Transcriptase Polymerase Chain Reaction; signal recognition particle; thylakoid translocase; thylakoids; Thylakoids - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.275.3.1529

Multiple sorting pathways operate in chloroplasts to localize proteins to the thylakoid membrane. The signal recognition particle (SRP) pathway in chloroplasts employs the function of a signal recognition particle (cpSRP) to target light harvesting chlorophyll-binding protein (LHCP) to the thylakoid membrane. In assays that reconstitute stroma-dependent LHCP integrationin vitro, the stroma is replaceable by the addition of GTP, cpSRP, and an SRP receptor homolog, cpFtsY. Still lacking is an understanding of events that take place at the thylakoid membrane including the identification of membrane proteins that may function at the level of cpFtsY binding or LHCP integration. The identification of Oxa1p in mitochondria, an inner membrane translocase component homologous to predicted proteins in bacteria and to the albino3 (ALB3) protein in thylakoids, led us to investigate the potential role of ALB3 in LHCP integration. Antibody raised against a 50-amino acid region of ALB3 (ALB3-50aa) identified a single 45-kDa thylakoid protein. Treatment of thylakoids with antibody to ALB3-50aa inhibited LHCP integration, whereas the same antibody treatment performed in the presence of antigen reversed the inhibition. In contrast, transport by the thylakoid Sec or Delta pH pathways was unaffected. These data support a model whereby a distinct translocase containing ALB3 is used to integrate LHCP into thylakoid membranes.