tailieunhanh - Báo cáo khoa học: The most C-terminal tri-glycine segment within the polyglycine stretch of the pea Toc75 transit peptide plays a critical role for targeting the protein to the chloroplast outer envelope membrane

The protein translocation channel at the outer envelope membrane of chloroplasts (Toc75) is synthesized as a larger precursor with an N-terminal transit peptide. Within the transit peptide of the pea Toc75, a major por-tion of the 10 amino acid long stretch that contains nine glycine residues was shown to be necessary for directing the protein to the chloroplast outer membranein vitro [Inoue K & Keegstra K (2003) Plant J34, 661–669]. | ềFEBS Journal The most C-terminal tri-glycine segment within the polyglycine stretch of the pea Toc75 transit peptide plays a critical role for targeting the protein to the chloroplast outer envelope membrane Amy J. Baldwin and Kentaro Inoue Department of Plant Sciences College of Agricultural EnvironmentalSciences University of California CA USA Keywords chloroplast protein translocation channel polyglycine protein targeting transit peptide tripeptide segment Correspondence K. Inoue Department of Plant Sciences College of Agricultural Environmental Sciences University of California One Shields Avenue Davis CA 95616 USA Fax 1 530 752 9659 Tel 1 530 752 7931 E-mail kinoue@ Received 18 January 2006 accepted 13 February 2006 doi The protein translocation channel at the outer envelope membrane of chloroplasts Toc75 is synthesized as a larger precursor with an N-terminal transit peptide. Within the transit peptide of the pea Toc75 a major portion of the 10 amino acid long stretch that contains nine glycine residues was shown to be necessary for directing the protein to the chloroplast outer membrane in vitro Inoue K Keegstra K 2003 Plant J 34 661-669 . In order to get insights into the mechanism by which the polyglycine stretch mediates correct targeting we divided it into three tri-glycine segments and examined the importance of each domain in targeting specificity in vitro. Replacement of the most C-terminal segment with alanine residues resulted in mistargeting the protein to the stroma while exchange of either of the other two tri-glycine regions had no effect on correct targeting. Furthermore simultaneous replacement of the N-terminal and middle tri-glycine segments with alanine repeats did not cause mistargeting of the protein as much as those of the N- and C-terminal or the middle and C-terminal segments. These results indicate that the most C-terminal tri-glycine segment is important for correct targeting. Exchanging .