Differential Role of HAMP-like Linkers in Regulating the Functionality of the Group III Histidine Kinase DhNik1p [Signal Transduction]

June 3rd, 2014 by Kaur, H., Singh, S., Rathore, Y. S., Sharma, A., Furukawa, K., Hohmann, S., Fnu, A., Mondal, A. K.

Nik1 orthologs are sensor kinases which function upstream of the HOG/p38 MAPK pathway in fungi. They contain a poly-HAMP module at their N-terminus which plays a pivotal role in osmosensing as well as fungal death upon exposure to fludioxonil. DhNik1p is a typical member of this class which contains five HAMP domains and four HAMP-like linkers. We investigated the contribution of each of the HAMP-like linker regions to the functionality of DhNik1p and found that the HAMP4b linker was essential as its deletion resulted in the complete loss of activity. Replacement of this linker with flexible peptide sequences did not restore DhNik1p activity. Thus, the HAMP-like sequence and possibly structural features of this linker region are indispensable for the kinase activity of DhNik1p. To gain insight into the global shape of the poly-HAMP module in DhNik1p (HAMP1-5), multi-angle laser and small angle X-ray scattering studies were carried out. Those data demonstrate that the MBP tagged HAMP1-5 protein exist as a dimer in solution with an elongated shape of maximum linear dimension ~365 angstrom. Placement of a sequence similarity based model of the HAMP1-5 protein inside experimental data-based model showed how two chains of HAMP1-5 are entwined on each other and the overall structure retained a periodicity. Normal mode analysis of the structural model is consistent with the H4b linker being a key to native-like collective motion in the protein. Overall, our shape-function studies reveal how the different elements in the HAMP1-5 structure mediate its function.