TY - JOUR
T1 - Role of HAMP domains in chemotaxis signaling by bacterial chemoreceptors
AU - Khursigara, Cezar M.
AU - Wu, Xiongwu
AU - Zhang, Peijun
AU - Lefman, Jonathan
AU - Subramaniam, Sriram
PY - 2008/10/28
Y1 - 2008/10/28
N2 - Bacterial chemoreceptors undergo conformational changes in response to variations in the concentration of extracellular ligands. These changes in chemoreceptor structure initiate a series of signaling events that ultimately result in regulation of rotation of the flagellar motor. Here we have used cryo-electron tomography combined with 3D averaging to determine the in situ structure of chemoreceptor assemblies in Escherichia coli cells that have been engineered to overproduce the serine chemoreceptor Tsr. We demonstrate that chemoreceptors are organized as trimers of receptor dimers and display two distinct conformations that differ principally in arrangement of the HAMP domains within each trimer. Ligand binding and methylation alter the distribution of chemoreceptors between the two conformations, with serine binding favoring the "expanded" conformation and chemoreceptor methylation favoring the "compact" conformation. The distinct positions of chemoreceptor HAMP domains within the context of a trimeric unit are thus likely to represent important aspects of chemoreceptor structural changes relevant to chemotaxis signaling. Based on these results, we propose that the compact and expanded conformations represent the "kinase-on" and "kinase-off" states of chemoreceptor trimers, respectively.
AB - Bacterial chemoreceptors undergo conformational changes in response to variations in the concentration of extracellular ligands. These changes in chemoreceptor structure initiate a series of signaling events that ultimately result in regulation of rotation of the flagellar motor. Here we have used cryo-electron tomography combined with 3D averaging to determine the in situ structure of chemoreceptor assemblies in Escherichia coli cells that have been engineered to overproduce the serine chemoreceptor Tsr. We demonstrate that chemoreceptors are organized as trimers of receptor dimers and display two distinct conformations that differ principally in arrangement of the HAMP domains within each trimer. Ligand binding and methylation alter the distribution of chemoreceptors between the two conformations, with serine binding favoring the "expanded" conformation and chemoreceptor methylation favoring the "compact" conformation. The distinct positions of chemoreceptor HAMP domains within the context of a trimeric unit are thus likely to represent important aspects of chemoreceptor structural changes relevant to chemotaxis signaling. Based on these results, we propose that the compact and expanded conformations represent the "kinase-on" and "kinase-off" states of chemoreceptor trimers, respectively.
KW - Cryo-electron tomography
KW - Molecular architecture
KW - Signal transduction
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U2 - 10.1073/pnas.0806401105
DO - 10.1073/pnas.0806401105
M3 - Article
C2 - 18940922
AN - SCOPUS:55949115430
SN - 0027-8424
VL - 105
SP - 16555
EP - 16560
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 43
ER -