Model for Membrane Organization and Protein Sorting in the Cyanobacterium <i>Synechocystis</i> sp. PCC 6803 Inferred from Proteomics and Multivariate Sequence Analyses

다국어 초록 (Multilingual Abstract)

<P>Cyanobacteria are unique eubacteria with an organized subcellular compartmentalization of highly differentiated internal thylakoid membranes (TM), in addition to the outer and plasma membranes (PM). This leads to a complicated system for transport and sorting of proteins into the different membranes and compartments. By shotgun and gel-based proteomics of plasma and thylakoid membranes from the cyanobacterium <I>Synechocystis</I> sp. PCC 6803, a large number of membrane proteins were identified. Proteins localized uniquely in each membrane were used as a platform describing a model for cellular membrane organization and protein intermembrane sorting and were analyzed by multivariate sequence analyses to trace potential differences in sequence properties important for insertion and sorting to the correct membrane. Sequence traits in the C-terminal region, but not in the N-terminal nor in any individual transmembrane segments, were discriminatory between the TM and PM classes. The results are consistent with a contact zone between plasma and thylakoid membranes, which may contain short-lived “hemifusion” protein traffic connection assemblies. Insertion of both integral and peripheral membrane proteins is suggested to occur through common translocons in these subdomains, followed by a potential translation arrest and structure-based sorting into the correct membrane compartment.</P><P>Are thylakoid and plasma membranes in <I>Synechocystis</I> (A) connected, or (B) physically separated? Integral membrane proteins with unique localization from proteomics were used for multivariate sequence property analyses. Different properties were found in the protein C-terminal tails. Since integral membrane proteins are cotranslationally inserted, this supports a common insertion site of these proteins for both membranes and a connection between them, allowing a restricted lateral diffusion to the final destination.</P><P><B>Graphic Abstract</B>
<IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jprobs/2011/jprobs.2011.10.issue-8/pr200268r/production/images/medium/pr-2011-00268r_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/pr200268r'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/pr200268r'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/pr200268r'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/pr200268r'>ACS Electronic Supporting Info</A></P>