TAILIEUCHUNG - Báo cáo Y học: The import of ferredoxin–NADP+ reductase precursor into chloroplasts is modulated by the region between the transit peptide and the mature core of the protein

Proteintransport acrossorganelles’membranes requires that precursorproteins adopt anunfoldedstructure inorder tobe translocatedby the importmachinery. Ferredoxin–NADP + reductaseprecursor, aswell asmanyothers, acquiresatightly foldedstructure thatneeds tobeunfoldedbeforeorduring its import. Several steps of chloroplast protein import are not fullyunderstood. Inparticular, the roleofdifferent regionsof the precursor protein has not been completely elucidated. | Eur. J. Biochem. 269 5431-5439 2002 FEBS 2002 doi The import of ferredoxin-NADP reductase precursor into chloroplasts is modulated by the region between the transit peptide and the mature core of the protein Daniela V. Rial Veronica A. Lombardo Eduardo A. Ceccarelli and Jorgelina Ottado Molecular Biology Division IBR Instituto de Biologia Molecular y Celular de Rosario CONICET Facultad de Ciencias Bioquimicas y Farmaceuticas Universidad Nacional de Rosario Rosario Argentina Protein transport across organelles membranes requires that precursor proteins adopt an unfolded structure in order to be translocated by the import machinery. Ferredoxin-NADP reductase precursor as well as many others acquires a tightly folded structure that needs to be unfolded before or during its import. Several steps of chloroplast protein import are not fully understood. In particular the role of different regions of the precursor protein has not been completely elucidated. In this work we have studied the import into chloroplasts of precursor proteins with inclusions of amino acid spacers between the transit peptide and the mature protein and with deletions in the N-terminal region of the mature enzyme. We measured the import rate constants for these precursors and the results indicate that the distance between the transit peptide and the core of the mature protein determines the import kinetics. The longer precursors were imported into the organelle faster than the wild type form. Precursors with deletions in the N-terminal region of the mature protein also showed increased import rates compared to the wild type. Homology studies amongst all family members reveal that only chloroplastic proteins possess this region. We suggest that even if the first amino acids of the mature protein do not contribute to its overall structural stability they condition the kinetic parameters of the import reaction. Besides the distance between the transit peptide and the .

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