  Receptors of bacterial chemotaxis form clusters at the cell poles, where
clusters act as "antennas" to amplify small changes in ligand concentration.
Interestingly, chemoreceptors cluster at multiple length scales. At the
smallest scale, receptors form dimers, which assemble into stable timers of
dimers. At a large scale, trimers form large polar clusters composed of
thousands of receptors. Although much is known about the signaling properties
emerging from receptor clusters, it is unknown how receptors localize at the
cell poles and what the cluster-size determining factors are. Here, we present
a model of polar receptor clustering based on coupled trimers of dimers, where
cluster size is determined as a minimum of the cluster-membrane free energy.
This energy has contributions from the cluster-membrane elastic energy,
penalizing large clusters due to their high intrinsic curvature, and
receptor-receptor coupling favoring large clusters. We find that the reduced
cluster-membrane curvature mismatch at the curved cell poles leads to large and
robust polar clusters in line with experimental observation, while lateral
clusters are efficiently suppressed.
