The aquatic bacterium Caulobacter crescentus has a two-step life cycle: it is born as a free-swimming “swarmer” and differentiates into an immobile “stalked” cell. As part of this process, it populates the two ends of the cell (poles) with macromolecular complexes that regulate these two different life forms. These specialized polar complexes in turn guide construction of flagellar motors and pili in swarmers and a holdfast structure in stalked forms, and regulate replication and segregation of the DNA chromosome as the cell grows and divides. A distinctive microdomain, formed by the disordered protein PopZ, has the job of marking the poles and gathering these macromolecular complexes (“client” proteins) that have pole-specific functions. PopZ forms a condensate (yellow) that acts as a defined membraneless microdomain, excluding large cytoplasmic molecules like ribosomes from the pole, and selectively recruiting client proteins. In this illustration, the microdomain is interacting with several soluble clients involved in regulation (orange), several membrane-bound clients (yellow-green), and DNA binding proteins (magenta).
This painting is part of PDB-101's SciArt gallery of Molecular Landscapes by David S. Goodsell.