Physical characterization of the manganese-sensing pneumococcal surface antigen repressor from Streptococcus pneumoniae

Biochemistry. 2013 Oct 29;52(43):7689-701. doi: 10.1021/bi401132w. Epub 2013 Oct 14.

Abstract

Transition metals, including manganese, are required for the proper virulence and persistence of many pathogenic bacteria. In Streptococcus pneumoniae (Spn), manganese homeostasis is controlled by a high-affinity Mn(II) uptake complex, PsaBCA, and a constitutively expressed efflux transporter, MntE. psaBCA expression is transcriptionally regulated by the DtxR/MntR family metalloregulatory protein pneumococcal surface antigen repressor (PsaR) in Spn. Here, we present a comprehensive analysis of the metal and DNA binding properties of PsaR. PsaR is a homodimer in the absence and presence of metals and binds two manganese or zinc atoms per protomer (four per dimer) in two pairs of structurally distinct sites, termed site 1 and site 2. Site 1 is likely filled with Zn(II) in vivo (K(Zn1) ≥ 10¹³ M⁻¹; K(Mn1) ≈ 10⁸ M⁻¹). The Zn(II)-site 1 complex adopts a pentacoordinate geometry as determined by X-ray absorption spectroscopy containing a single cysteine and appears to be analogous to the Cd(II) site observed in Streptococcus gordonii ScaR. Site 1 is necessary but not sufficient for full positive allosteric activation of DNA operator binding by metals as measured by ΔGc, the allosteric coupling free energy, because site 1 mutants show an intermediate ΔGc. Site 2 is the primary regulatory site and governs specificity for Mn(II) over Zn(II) in PsaR, where ΔGc(Zn,Mn) >> ΔGc(Zn,Zn) despite the fact that Zn(II) binds site 2 with an affinity 40-fold higher than that of Mn(II); i.e., K(Zn2) > K(Mn2). Mutational studies reveal that Asp7 in site 2 is a critical ligand for Mn(II)-dependent allosteric activation of DNA binding. These findings are discussed in the context of other well-studied DtxR/MntR Mn(II)/Fe(II) metallorepressors.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Allosteric Site
  • Amino Acid Substitution
  • Antigens, Bacterial / chemistry*
  • Antigens, Bacterial / genetics
  • Antigens, Bacterial / metabolism
  • Antigens, Surface / chemistry*
  • Antigens, Surface / genetics
  • Antigens, Surface / metabolism
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Chemical Phenomena
  • Cysteine / chemistry
  • Dimerization
  • Kinetics
  • Manganese / metabolism*
  • Models, Molecular*
  • Molecular Weight
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • Mutation, Missense
  • Operator Regions, Genetic
  • Protein Stability
  • Protein Structure, Quaternary
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Repressor Proteins / chemistry*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Streptococcus pneumoniae / metabolism*
  • Zinc / metabolism

Substances

  • Antigens, Bacterial
  • Antigens, Surface
  • Bacterial Proteins
  • MntR protein, bacteria
  • Mutant Proteins
  • Recombinant Proteins
  • Repressor Proteins
  • Manganese
  • Zinc
  • Cysteine