Member of the two-component regulatory system GraR/GraS involved in resistance against cationic antimicrobial peptides (CAMPs). Functions as a sensor protein kinase which phosphorylates GraR through the auxiliary protein GraX. In turn, GraR up-regulates many genes such as adhesins, exoproteins, transporters, toxins, and proteins involved in cell wall synthesis. Down-regulates the expression of many genes involved in RNA and amino acid synthesis or glycolysis. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Interacts with GraX.