This is a family of KdpD sensor kinase proteins that regulate the kdpFABC operon responsible for potassium transport [1]. The aligned region corresponds to the N-terminal cytoplasmic part of the protein which functions as the sensor domain responsible for sensing turgor pressure [2]. It recognises C-di-AMP and K+ (Matilla et.al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: The kdp system of Clostridium acetobutylicum: cloning, sequencing, and transcriptional regulation in response to potassium concentration. Treuner-Lange A, Kuhn A, Durre P; J Bacteriol 1997;179:4501-4512. PMID:9226259

2: KdpD and KdpE, proteins that control expression of the kdpABC operon, are members of the two-component sensor-effector class of regulators. Walderhaug MO, Polarek JW, Voelkner P, Daniel JM, Hesse JE, Altendorf K, Epstein W; J Bacteriol 1992;174:2152-2159. PMID:1532388