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Abstract:
Protein gradients play a central role in the spatial organization of
cells, but the mechanisms of their formation are incompletely
understood. This study analyzes the determinants responsible for
establishing bipolar gradients of the ATPase MipZ, a key regulator of
division site placement in Caulobacter crescentus. We have solved the
crystal structure of MipZ in different nucleotide states, dissected its
ATPase cycle, and investigated its interaction with FtsZ, ParB, and the
nucleoid. Our results suggest that the polar ParB complexes locally
stimulate the formation of ATP-bound MipZ dimers, which are then
retained near the cell poles through association with chromosomal DNA.
Due to their intrinsic ATPase activity, dimers eventually dissociate
into freely diffusible monomers that undergo spontaneous nucleotide
exchange and are recaptured by ParB. These findings clarify the
molecular function of a conserved gradient-forming system and reveal
mechanistic principles that might be commonly used to sustain protein
gradients within cells.
