Member of the two-component regulatory system GraR/GraS involved in resistance against cationic antimicrobial peptides (CAMPs) (PubMed:17502406, PubMed:18518949). Functions as a sensor protein kinase which phosphorylates GraR through the auxiliary protein GraX (PubMed:25685323). In turn, GraR up-regulates many genes such as adhesins, exoproteins, transporters, toxins, and proteins involved in cell wall synthesis (PubMed:21765893). Down-regulates the expression of many genes involved in RNA and amino acid synthesis or glycolysis. Confers resistance to vancomycin, polymyxin B, lysozyme and LL-37 (PubMed:17502406, PubMed:17676995, PubMed:18518949). ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Interacts with GraX. Does not seem to possess an autophosphorylation activity.