205016620
Structure of the gating domain of a Ca2+-activated K+ channel complexed with Ca2+/calmodulin
Small-conductance Ca2+-activated K+ channels (SK channels) are independent of voltage and gated solely by intracellular Ca2+. These membrane channels are heteromeric complexes that comprise pore-forming α-subunits and the Ca2+-binding protein calmodulin (CaM). CaM binds to the SK channel through the CaM-binding domain (CaMBD), which is located in an intracellular region of the α-subunit immediately carboxy-terminal to the pore. Channel opening is triggered when Ca2+ binds the EF hands in the N-lobe of CaM. Here we report the 1.60 Å crystal structure of the SK channel CaMBD/Ca2+/CaM complex. The CaMBD forms an elongated dimer with a CaM molecule bound at each end; each CaM wraps around three α-helices, two from one CaMBD subunit and one from the other. As only the CaM N-lobe has bound Ca2+, the structure provides a view of both calcium-dependent and -independent CaM/protein interactions. Together with biochemical data, the structure suggests a possible gating mechanism for the SK channel.
38152937
Structural Mechanisms of QacR Induction and Multidrug Recognition
The Staphylococcus aureus multidrug binding protein QacR represses transcription of the qacA multidrug transporter gene and is induced by structurally diverse cationic lipophilic drugs. Here, we report the crystal structures of six QacR-drug complexes. Compared to the DNA bound structure, drug binding elicits a coil-to-helix transition that causes induction and creates an expansive multidrug-binding pocket, containing four glutamates and multiple aromatic and polar residues. These structures indicate the presence of separate but linked drug-binding sites within a single protein. This multisite drug-binding mechanism is consonant with studies on multidrug resistance transporters.
22785877
Structures of the pleiotropic translational regulator Hfq and an Hfq-RNA complex: a bacterial Sm-like protein.
In prokaryotes, Hfq regulates translation by modulating the structure of numerous RNA molecules by binding preferentially to A/U-rich sequences. To elucidate the mechanisms of target recognition and translation regulation by Hfq, we determined the crystal structures of the Staphylococcus aureus Hfq and an Hfq-RNA complex to 1.55 and 2.71 A resolution, respectively. The structures reveal that Hfq possesses the Sm-fold previously observed only in eukaryotes and archaea. However, unlike these heptameric Sm proteins, Hfq forms a homo-hexameric ring. The Hfq-RNA structure reveals that the single-stranded hepta-oligoribonucleotide binds in a circular conformation around a central basic cleft, whereby Tyr42 residues from adjacent subunits stack with six of the bases, and Gln8, outside the Sm motif, provides key protein-base contacts. Such binding suggests a mechanism for Hfq function.
4431121
Crystal structures of SarA, a pleiotropic regulator of virulence genes in S. aureus
Staphylococcus aureus is a major human pathogen, the potency of which can be attributed to the regulated expression of an impressive array of virulence determinants. A key pleiotropic transcriptional regulator of these virulence factors is SarA, which is encoded by the sar (staphylococcal accessory regulator) locus. SarA was characterized initially as an activator of a second virulence regulatory locus, agr, through its interaction with a series of heptad repeats (AGTTAAG) within the agr promoter. Subsequent DNA-binding studies have revealed that SarA binds readily to multiple AT-rich sequences of variable lengths. Here we describe the crystal structure of SarA and a SarA–DNA complex at resolutions of 2.50 Å and 2.95 Å, respectively. SarA has a fold consisting of a four-helix core region and ‘inducible regions’ comprising a β-hairpin and a carboxy-terminal loop. On binding DNA, the inducible regions undergo marked conformational changes, becoming part of extended and distorted α-helices, which encase the DNA. SarA recognizes an AT-rich site in which the DNA is highly overwound and adopts a D-DNA-like conformation by indirect readout. These structures thus provide insight into SarA-mediated transcription regulation.
837237
Crystal structures of apocalmodulin and an apocalmodulin/SK potassium channel gating domain complex.
Small conductance Ca2+-activated K+ channels (SK channels) are composed of the pore-forming alpha subunit and calmodulin (CaM). CaM binds to a region of the alpha subunit called the CaM binding domain (CaMBD), located intracellular and immediately C-terminal to the inner helix gate, in either the presence or absence of Ca2+. SK gating occurs when Ca2+ binds the N lobe of CaM thereby transmitting the signal to the attached inner helix gate to open. Here we present crystal structures of apoCaM and apoCaM/SK2 CaMBD complex. Several apoCaM crystal forms with multiple (12) packing environments reveal the same EF hand domain-swapped dimer providing potentially new insight into CaM regulation. The apoCaM/SK2 CaMBD structure, combined with our Ca2+/CaM/CaMBD structure suggests that Ca2+ binding induces folding and dimerization of the CaMBD, which causes large CaMBD-CaM C lobe conformational changes, including a >90 degrees rotation of the region of the CaMBD directly connected to the gate.
29559148
Structural basis for the recognition of a bisphosphorylated MAP kinase peptide by human VHR protein Phosphatase.
Human VHR (vaccinia H1 related phosphatase) is a member of the dual-specificity phosphatases (DSPs) that often act on bisphosphorylated protein substrates. Unlike most DSPs, VHR displays a strong preference for dephosphorylating phosphotyrosine residues over phosphothreonine residues. Here we describe the 2.75 A crystal structure of the C124S inactive VHR mutant in complex with a bisphosphorylated peptide corresponding to the MAP kinase activation lip. This structure and subsequent biochemical studies revealed the basis for the strong preference for hydrolyzing phosphotyrosine within bisphosphorylated substrates containing -pTXpY-. In the structure, the two phospho residues are oriented into distinct pockets; the phosphotyrosine is bound in the exposed yet deep active site cleft while the phosphothreonine is loosely tethered into a nearby basic pocket containing Arg(158). As this structure is the first substrate-enzyme complex reported for the DSP family of enzymes, these results provide the first glimpse into how DSPs bind their protein substrates.
6747128
Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector
The prospects for the measurement of the tensor structure of the vertex between a standard model Higgs boson and two weak gauge bosons using the distribution of the azimuthal angles between the two tagging jets in the weak boson fusion channel are studied in a Monte Carlo analysis using the fast simulation of the ATLAS detector. The decay channels H→τ+τ-→ll+4ν, H→τ+τ-→lh+3ν at mH=120 GeV and H→W+W-→llνν at mH=160 GeV are used in the analysis. For a standard model Higgs boson it is found that purely anomalous couplings are expected to be excluded at a confidence level corresponding to 2σ or more at mH=120 GeV and more than 5σ at mH=160 GeV from 30 fb-1 of data. With a value of 1 roughly reproducing the standard model cross section for a purely anomalous coupling, the standard deviation in a measurement of a contribution of a CP even anomalous coupling in addition to the standard model coupling is estimated to be 0.20 at mH=120 GeV and 0.09 at mH=160 GeV.
8372632
Investigation of the Discovery Potential for Higgs Bosons of the Minimal Supersymmetric Extension of the Standard Model (MSSM) with ATLAS
The discovery potential of the ATLAS experiment at the LHC for Higgs bosons of the MSSM is discussed. Several CP conserving and one CP violating benchmark scenario are investigated.
117815253
Higgs Boson Searches with ATLAS based on 2010 Data
The results of Higgs Boson searches with the ATLAS detector based on 2010 proton proton collision data corresponding to integrated luminosities of up to 39 pb-1are presented. Searches for H --> 2 photons, H --> W+W- --> l+l- 2 neutrinos and H --> ZZ --> l+l- 2 neutrinos / l+l- qqbar in the context of the Standard Model (SM), for H--> tau+ tau- in the context of the Minimal Supersymmetric Extension of the Standard Model (MSSM) and for a generic scalar at low mass in the vicinity of the Ypsilon resonance decaying to a pair of muons are discussed. All observations are in agreement with the expectations from the background-only hypothesis. Hence exclusion limits at 95% confidence level are derived
119439280
Higgs Physics at a Future e+e- Linear Collider
This letter reviews the potential of a high luminosity e+e- linear collider (LC) in the precision study of the Higgs boson profile. The complementarity with the Large Hadron Collider (LHC) Higgs physics program is briefly discussed.
2506186
Model-independent determination of the top Yukawa coupling from LHC and ILC
We show how a measurement of the process pp→tt̄H0+X at the Large Hadron Collider (LHC) and a measurement of the Higgs boson branching ratios BR(H0→bb̄) and BR(H0→W+W-) at a future linear electron positron collider (ILC) can be combined to extract a value of the top quark Yukawa coupling in a model-independent way. We find that for masses with 120 GeV/c2<mH<200 GeV/c2 a measurement precision of 15% including systematic uncertainties can be achieved for integrated luminosities of 300 fb-1 at the LHC and 500 fb-1 at the ILC at a centre-of-mass energy of 350 GeV. 