Phosphorylated aspartate in the structure of a response regulator protein

Phosphorylation of aspartic acid residues is the hallmark of two-component signal transduction systems that orchestrate the adaptive responses of micr o-organisms to changes in their surroundings. Two-component systems consist of a sensor kinase that interprets environmental signals and a response re gulator that activates the appropriate physiological response. Although str uctures of response regulators are known, little is understood about their activated phosphorylated forms, due to the intrinsic instability of the aci d phosphate linkage. Here, we report the phosphorylated structure of the re ceiver/phosphoacceptor domain of Spo0A, the master regulator of sporulation , from Bacillus stearothermophilus. The phosphoryl group is covalently bond ed to the invariant aspartate 55, and co-ordinated to a nearby divalent met al cation, with both species fulfilling their electrostatic potential throu gh interactions with solvent water molecules, the protein main chain, and w ith side-chains of amino acid residues strongly conserved across the respon se regulator family. This is the first direct visualisation of a phosphoryl group covalently linked to an aspartic acid residue in any protein, with i mplications for signalling within the response regulator family. (C) 1999 A cademic Press.