FixK₂, a key regulator in Bradyrhizobium japonicum, is a substrate for the protease ClpAP in vitro

Abstract

FixK₂ is a CRP-like transcription factor that controls the endosymbiotic lifestyle of Bradyrhizobium japonicum. The reason for its noticeable protease sensitivity was explored here. The repertoire of Clp chaperone-proteases in B. japonicum was examined, and specifically ClpAP₁ and ClpXP₁ were purified and tested. FixK₂ was found to be degraded by ClpAP₁ but not by ClpXP₁. Degradation was inhibited by the ClpS₁ adaptor protein, indicating that FixK₂ is a direct substrate for ClpAP₁. The last 12 amino acids of FixK₂ appeared to be recognized by ClpA. The results suggest that the ClpAP system is involved in the cellular turnover of FixK₂.