Regulation of the GTPase Cycle in Post-translational Signal Recognition Particle-based Protein Targeting Involves cpSRP43

• Published in: The Journal of biological chemistry Vol. 279; no. 41; pp. 43077 - 43084
• Main Authors: Goforth, Robyn L, Peterson, Eric C, Yuan, Jianguo, Moore, Misty J, Kight, Alicia D, Lohse, Matthew B, Sakon, Joshua, Henry, Ralph L
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 08.10.2004
• Subjects: Amino Acid Sequence; Ankyrins - chemistry; Apoproteins - chemistry; Arabidopsis; Biological Transport; Chloroplast Proteins; Chloroplasts - chemistry; Chloroplasts - metabolism; Cloning, Molecular; Electrophoresis, Polyacrylamide Gel; Endoplasmic Reticulum - metabolism; Gene Deletion; Glutathione Transferase - metabolism; GTP Phosphohydrolases - chemistry; Hydrolysis; Models, Molecular; Molecular Sequence Data; Peptides - chemistry; Photosystem II Protein Complex - chemistry; Plant Proteins - chemistry; Protein Biosynthesis; Protein Processing, Post-Translational; Protein Structure, Tertiary; Recombinant Fusion Proteins - chemistry; Ribosomes - chemistry; Signal Recognition Particle - chemistry; Signal Recognition Particle - physiology; Signal Transduction; Thylakoids - metabolism; Two-Hybrid System Techniques
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M401600200

The chloroplast signal recognition particle consists of a conserved 54-kDa GTPase and a novel 43-kDa chromodomain protein (cpSRP43) that together bind light-harvesting chlorophyll a/b-binding protein (LHCP) to form a soluble targeting complex that is subsequently directed to the thylakoid membrane. Homology-based modeling of cpSRP43 indicates the presence of two previously identified chromodomains along with a third N-terminal chromodomain. Chromodomain deletion constructs were used to examine the role of each chromodomain in mediating distinct steps in the LHCP localization mechanism. The C-terminal chromodomain is completely dispensable for LHCP targeting/integration in vitro . The central chromodomain is essential for both targeting complex formation and integration because of its role in binding the M domain of cpSRP54. The N-terminal chromodomain (CD1) is unnecessary for targeting complex formation but is required for integration. This correlates with the ability of CD1 along with the ankyrin repeat region of cpSRP43 to regulate the GTPase cycle of the cpSRP-receptor complex.