Structure And Properties Of Metalloregulatory Protein PbrR

Metal ion play a key role in life system and most prokaryotes control metal homeostasis strictly by the regulation of Metalloregulatory protein.R.metallidurans CH34 maintain a strict cellular divalent lead quota within a narrow range,by using pbr operon encodes proteins involved in sensing and transport of divalent lead ion.Expression of the pbr operon is under tightly controled by PbrR,a member of the MerR family of dualfunction transcriptional regulators.It was the first metalloprotein that was founded in nature with highest specificity recognition to divalent lead ion.Earlier studies of other MerR family members show that prokaryotes regulatory proteins both repress and activate transcription by differentially modulating DNA structure within the promoter.The metal free,apo metalloregulatory proteins bind the promoter DNA as a repressor state to precluding optimal RNA polymerase-promoter recognition.Proteins would convert into an activator conformation upon binding a metal in the allosteric site and then slightly bend the promoter DNA.So it is important to study the structure and molecular mechanism of PbrR with Pb2+.To understand how PbrR interacts with divalent lead and metal sensitivity at atomic level,we solved the 2.0? X-ray crystal structure of PbrR-Pb2+binding complex.In the homodimer structure of metal-bound forms,the lead(?)is buried in a solvent-inaccessible site which restrict the metal to a hemidirected coordinate geometry with three conserved residues Cys78,Cys113 and Cys122.The PbrR-Pb2+structure which to our knowledge offers the first view of a hemidirected Pb2+-thiolate in a metalloprotein,this binding mode is rare but well suited for ultrasensitive genetic switch.Chelator(EDTA)competition binding experiment reveal that PbrR appear to bind Pb2+with extremely high affinity,KPb=1.23(±0.13)×1013 M-1.These findings are critical important for us to understand the sensitivity,selectivity and regulation of MerR family proteins.