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Structure of the basal components of a bacterial transporter
Jeffrey Meisner, Tatsuya Maehigashi, Ingemar André, Christine M. Dunham and Charles P. Moran, Jr.
Proceedings of the National Academy of Sciences of the United States of America
Vol. 109, No. 14 (April 3, 2012), pp. 5446-5451
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/41588174
Page Count: 6
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Proteins SpoIIQ and SpoIIIAH interact through two membranes to connect the forespore and the mother cell during endospore development in the bacterium Bacillus subtilis. SpolllAH consists of a transmembrane segment and an extracellular domain with similarity to YscJ proteins. YscJ proteins form large multimeric rings that are the structural scaffolds for the assembly of type III secretion systems in Gram-negative bacteria. The predicted ringforming motif of SpolllAH and other evidence led to the model that SpollQ and SpolllAH form the core components of a channel or transporter through which the mother cell nurtures forespore development. Therefore, to understand the roles of SpolllAH and SpollQ in channel formation, it is critical to determine whether SpolllAH adopts a ring-forming structural motif, and whether interaction of SpolllAH with SpollQ would preclude ring formation. We report a 2.8-Â resolution structure of a complex of SpollQ and SpolllAH. SpolllAH folds into the ring-building structural motif, and modeling shows that the structure of the SpollQ-SpolllAH complex is compatible with forming a symmetrical oligomer that is similar to those in type III systems. The inner diameters of the two most likely ring models are large enough to accommodate several copies of other integral membrane proteins. SpollQ contains a LytM domain, which is found in metalloendopeptidases, but lacks residues important for metalloprotease activity. Other LytM domains appear to be involved in protein-protein interactions. We found that the LytM domain of SpollQ contains an accessory region that interacts with SpoIIIAH.
Proceedings of the National Academy of Sciences of the United States of America © 2012 National Academy of Sciences