Molecular Interactions of Bacterial Chemoreceptor Assemblies

Bacterial chemoreceptors form homodimers that assemble into large clusters on cell membranes to respond to external signals. These clusters have been found to have two different types of patterns: one is composed of inverted pyramid like trimers-of-dimers observed in the X-ray crystal structures, and the other is formed by the zipper like overlap of tips of dimers, as revealed by low-resolution electron microscopy. The detailed molecular model of the zipper like assemblies has remained unknown until now. Using protein-protein docking method, we studied the interactions between serine chemoreceptor Tsr dimers in Escherichia coli. The basic complexes for the two types of clustering patterns were both found in the docking complexes. Molecular dynamics simulations confirmed that these complexes were stable to a certain extent. Protein-protein interface analysis indicated that electrostatic and hydrophobic interactions are the dominant driving forces for zipper like complex formation. Arg388, Phe373, and Ile377 are the key interfacial residues that stabilize the zipper like complexes. The molecular models for the zipper like complexes provide insight into the mechanisms of bacterial chemoreceptor assemblies on membranes and serve as a basis for further theoretical and simulation studies.