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Abstract Detail


Protein Targeting and Vesicular Trafficking

Hsu, Shih-Chi [1], Inoue, Kentaro [2].

Towards understanding targeting mechanisms of chloroplastic β-barrel membrane proteins.

Beta-barrel proteins are a distinct class of outer membrane proteins in chloroplasts, mitochondria and Gram-negative bacteria. In chloroplasts, five putative β-barrel membrane proteins, Toc75, OEP21, OEP24, OEP37, and OEP80, have been identified and their functions have been experimentally examined or deduced via structural predictions. The evidently conserved targeting mechanisms for mitochondrial and bacterial β-barrel membrane proteins which include soluble intermediates have been elucidated recently. By contrast, little is known regarding the targeting mechanism of chloroplastic β-barrel membrane proteins except Toc75 which depends its correct targeting on a unique bipartite transit peptide. To better understand the molecular details of chloroplast development and also membrane biogenesis, we examined the in vitro import requirements of the putative chloroplastic β-barrel membrane proteins. By protease-pretreatment assays, we found that all of them required proteinaceous components in the outer envelope of chloroplasts for import. We also showed that the requirement of nucleotide triphosphates (NTPs) for and the dependency on the general pathway of the import efficiency in vitro were distinct between the five putative β-barrel proteins by biochemically depleting NTPs from and incorporating a bacteria-produced general pathway substrate in the assay mixtures, respectively. Finally, we have not been able to detect any soluble intermediates in the import reactions, implying that chloroplastic β-barrel proteins may not use the pathway conserved in mitochondria and bacteria. Our results suggest the presence of multiple pathways for β-barrel membrane protein targeting to the outer envelope of chloroplasts.


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1 - University of California, Davis, Plant Sciences, Rm 222, Asmundson Hall, University of California, Davis, One Shields Ave, Davis, california, 95616, USA
2 - University of California, Davis, Plant Sciences

Keywords:
chloroplast protein transport
outer envelope protein
beta-barrel membrane protein.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P22005
Abstract ID:186


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