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Abstract:
It is now over ten years since the first structure of a HAMP domain led us to propose the gearbox model of signal transduction in bacterial transmembrane receptors. Under this model, signals generated in extracellular sensor domains are transmitted to the cytoplasm by rotation of linking helices to interconvert specific coiled-coil packing states. So how has this model stood the test of time? From that single example, the number of HAMP domain structures has grown to dozens. In keeping with the original model, this structural diversity now covers the full range of originally anticipated rotation states. But is there more? We present new structures of the poly-HAMP array from a family of proteins that contain up to 57 contiguous HAMP domains. These form tightly organized, rod-like structures underpinned by an astounding degree of sequence conservation. Further, these structures hint at a new domain of potential signaling states by rotations opposite to those previously observed. Deletion or truncation of poly-HAMP arrays in fungal proteins is associated with morphological defects and resistance to fungicides, suggesting a new role for HAMP domains in direct sensing in the cytoplasm.
