title: Binding of Cyclic Di-AMP to the Staphylococcus aureus Sensor Kinase KdpD Occurs via the Universal Stress Protein Domain and Downregulates the Expression of the Kdp Potassium Transporter.
abstract: Nucleotide signaling molecules are important intracellular messengers that regulate a wide range of biological functions. The human pathogen Staphylococcus aureus produces the signaling nucleotide cyclic di-AMP (c-di-AMP). This molecule is common among Gram-positive bacteria and in many organisms is essential for survival under standard laboratory growth conditions. In this study, we investigated the interaction of c-di-AMP with the S. aureus KdpD protein. The sensor kinase KdpD forms a two-component signaling system with the response regulator KdpE and regulates the expression of the kdpDE genes and the kdpFABC operon coding for the Kdp potassium transporter components. Here we show that the S. aureus KdpD protein binds c-di-AMP specifically and with an affinity in the micromolar range through its universal stress protein (USP) domain. This domain is located within the N-terminal cytoplasmic region of KdpD, and amino acids of a conserved SXS-X20-FTAXY motif are important for this binding. We further show that KdpD2, a second KdpD protein found in some S. aureus strains, also binds c-di-AMP, and our bioinformatics analysis indicates that a subclass of KdpD proteins in c-di-AMP-producing bacteria has evolved to bind this signaling nucleotide. Finally, we show that c-di-AMP binding to KdpD inhibits the upregulation of the kdpFABC operon under salt stress, thus indicating that c-di-AMP is a negative regulator of potassium uptake in S. aureus.
  
  
  OBJECTIVE
  Staphylococcus aureus is an important human pathogen and a major cause of food poisoning in Western countries. A common method for food preservation is the use of salt to drive dehydration. This study sheds light on the regulation of potassium uptake in Staphylococcus aureus, an important aspect of this bacterium's ability to tolerate high levels of salt. We show that the signaling nucleotide c-di-AMP binds to a regulatory component of the Kdp potassium uptake system and that this binding has an inhibitory effect on the expression of the kdp genes encoding a potassium transporter. c-di-AMP binds to the USP domain of KdpD, thus providing for the first time evidence for the ability of such a domain to bind a cyclic dinucleotide.
authors.affiliation: Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom.
authors.forename: Joana A
authors.initials: JA
authors.lastname: Moscoso
authors.affiliation: Center for Integrated Protein Science (CiPSM), Department of Biology I, Microbiology, Ludwig-Maximilians-Universität München, Martinsried, Germany.
authors.forename: Hannah
authors.initials: H
authors.lastname: Schramke
authors.affiliation: Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom.
authors.forename: Yong
authors.identifier: http://orcid.org/0000-0003-2968-0081
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Tosi
authors.affiliation: Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom.
authors.forename: Amina
authors.initials: A
authors.lastname: Dehbi
authors.affiliation: Center for Integrated Protein Science (CiPSM), Department of Biology I, Microbiology, Ludwig-Maximilians-Universität München, Martinsried, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Jung
authors.affiliation: Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London, United Kingdom a.grundling@imperial.ac.uk.
authors.forename: Angelika
authors.identifier: http://orcid.org/0000-0002-6235-8687
authors.initials: A
authors.lastname: Gründling
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D015226:Dinucleoside Phosphates / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D010802:Phylogeny; D011188:Potassium / Q000378:metabolism*; D011485:Protein Binding; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D015226:Dinucleoside Phosphates; C528998:cyclic diadenosine phosphate; D011494:Protein Kinases; C075616:kdpD protein, Bacteria; D011188:Potassium