Abstract
Many membrane proteins are known to form higher-order oligomers, but the degree to which membrane regions could facilitate protein complex assembly remains largely unclear. Clusters of chemotaxis receptors are among the most prominent structures in the bacterial cell membrane, and they play important functions in processing of chemotactic signals. Although much work has been done to elucidate mechanisms of cluster formation, it almost exclusively focused on cytoplasmic interactions among receptors and other chemotaxis proteins, whereas involvement of membrane-mediated interactions was only hypothesized. Here we used imaging of constructs composed of only a fluorescent protein and the TM helices of Tar to demonstrate that interactions between the lipid bilayer and transmembrane (TM) helices of Escherichia coli chemoreceptors alone are sufficient to mediate clustering. We found that the ability to cluster depends on the sequence or length of the TM helices, implying that certain conformations of these helices facilitate clustering, whereas others do not. Notably, observed sequence specificity was apparently consistent with differences in clustering between native E. coli receptors, with the TM sequence of better-clustering high-abundance receptors being more efficient in promoting membrane-mediated complex formation. These results indicate that being more than just membrane anchors, TM helices could play an important role in the clustering and organization of membrane proteins in bacteria.
Highlights
Many membrane proteins are known to form higher-order oligomers, but the degree to which membrane regions could facilitate protein complex assembly remains largely unclear
We used imaging of constructs composed of only a fluorescent protein and the TM helices of Tar to demonstrate that interactions between the lipid bilayer and transmembrane (TM) helices of Escherichia coli chemoreceptors alone are sufficient to mediate clustering
These results indicate that being more than just membrane anchors, TM helices could play an important role in the clustering and organization of membrane proteins in bacteria
Summary
Many membrane proteins are known to form higher-order oligomers, but the degree to which membrane regions could facilitate protein complex assembly remains largely unclear. Coli and in most other motile bacteria (2, 8 –10), providing a prime example to study factors that influence subcellular localization and higher order oligomerization of bacterial proteins These large macromolecular clusters have currently been established to have a universal architecture composed of a hexagonal lattice where trimers of receptor dimers are bridged by the chemotaxis proteins CheA and CheW [11, 12]. Recent models, which could account for subcellular localization and clustering of the chemoreceptor in the absence of CheA and CheW, are based on interactions between receptors and the lipid bilayer These models suggest that receptors could partition into parts of the bilayer that match the height of their transmembrane (TM) helices while simultaneously deforming the bilayer, which acts as an attractive force to promote receptor clustering [20]. Chemoreceptor interactions with the membrane might play a key role in the polar localization of receptors, whereby curvature mismatch between the
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