<i>(A)</i> Three ArsTM monomers form the trimeric ring.

<p>This flat ring encloses a ~15 Å diameter inner void. <b><i>(B)</i></b> Interaction surface between two monomers that form the trimeric ring. The forces that stabilise the trimeric ring include salt bridges as well as hydrophobic interactions between the N-terminal of a single monomer to the C-terminal of a nearby monomer in a continuous manner.</p

Congruency of the phylogenetic trees based on <i>(A)</i> MamA protein sequences and on <i>(B)</i> 16S rRNA gene sequences that reflect the evolution of MTB.

<p>Scale bars represent the percentage sequence divergence. Bootstrap values at nodes are percentages of 100 replicates. The MTB from <i>Alphaproteobacteria</i> class used in the analyses are: <i>Magnetospirillum magnetotacticum</i> (strain MS-1), <i>Ms</i>. <i>magneticum</i> (AMB-1), <i>Ms</i>. <i>gryphiswaldense</i> (MSR-1), strain SO-1, strain LM-1, <i>Magnetovibrio blakemorei</i> (MV-1), <i>Magnetospira</i> sp. QH-2, strain MO-1, <i>Magnetofaba australis</i> (IT-1) and <i>Magnetococcus marinus</i> (MC-1). Strain SS-5 from the <i>Gammaproteobacteria</i> class is also used. From the <i>Deltaproteobacteria</i> class MTB used include the magnetotactic multicellular prokaryotes <i>Ca</i>. Magnetoglobus multicellularis (MMP) and strain HK-1, <i>Ca</i>. Desulfamplus magnetomortis (BW-1), <i>Desulfovibrio magneticus</i> (RS-1 and FH-1), and strain ML-1. <i>Ca</i>. Magnetobacterium bavaricum (Mbav) and strain MYR-1 of the <i>Nitrospirae</i> phylum was also used. Accession numbers are shown in parenthesis.</p

Correction: MamA as a Model Protein for Structure-Based Insight into the Evolutionary Origins of Magnetotactic Bacteria

<p>Correction: MamA as a Model Protein for Structure-Based Insight into the Evolutionary Origins of Magnetotactic Bacteria</p

ArsTM crystal packing, asymmetric unit composition and overall structure.

<p><b><i>(A)</i></b> ArsTM crystal packing and asymmetric unit composition. The molecules are shown in three rotation-related views. <b><i>(B)</i></b> Overlay of all six ArsTM monomers reveals the high degree of structural similarity. The representative ArsTM monomer contains five sequential TPR motifs. The molecule is shown in two views, related by a 90° rotation. <b><i>(C)</i></b> An overlay of representative monomers from ArsTM (green), MamAΔ41_Mbav (PDB ID: 3VTX, orange) and <i>Magnetospirillum</i> species MamAΔ41_AMB-1 (PDB ID: 3AS5 chain A and B in light pink and brown, respectively) related by a 180° rotation. A high structural similarity of MamAΔ41 between the species can be observed, apart from the helical conformation of the identical His-tag linker sequence remaining after thrombin proteolysis (H11: ELALVPR) seen in the 3AS5 chain B and 3VTX. In addition, a light flexibility is observed at the NTD of the monomers. All images were produced by PyMOL.</p

ConSurf analysis shows a high degree of structural conservation between ArsTM and MamA from alternative species, though this is largely limited to the concave surface and a cluster around the fifth TPR and the C-terminal.

<p>All sequences used in this analysis are shown in the multiple sequence alignment of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130394#pone.0130394.s002" target="_blank">S2 Fig</a>.</p

Crystallographic data for ArsTM.

<p>Crystallographic data for ArsTM.</p

Circular dichroism measurements of ArsTM (purple) and MamAΔ41 proteins from RS-1 (Blue) Mbav (orange), AMB-1 (green) and MSR-1 (red).

<p>(A) Circular dichroism spectra. (B) Circular dichroism melting curve measurements at 222 nm. Wild type MamAΔ41_RS-1 presents the lowest thermostability, with a melting temperature of ~40°C, while the triple mutated MamAΔ41_RS-1 (ArsTM) exhibits a slightly increased thermostability with a melting temperature of ~ 51°C. MamAΔ41_AMB-1, MamAΔ41_MSR-1 and MamAΔ41_Mbav present melting temperatures of ~51, 53 and 65°C, respectively.</p

NTD stabilisation of MamAΔ41 from different species.

<p><b><i>(A)</i></b> Detailed representation of the interactions stabilising the ArsTM NTD. The ArsTM NTD is stabilised by a diverse network of hydrophobic interactions. <b><i>(B)</i></b> Detailed representation of the interactions stabilising the MamAΔ41_Mbav NTD. The MamAΔ41_Mbav NTD is stabilised by a diverse network of hydrogen bonds and a single non-conserved salt bridge. <b><i>(C)</i></b> Detailed representation of the interactions stabilising the MamAΔ41_AMB-1 NTD. The MamAΔ41_AMB-1 NTD is stabilised through numerous hydrophobic interactions, a few hydrogen bonds and a single conserved salt bridge. Both NTD domains are shown in two views, related by a 90° rotation.</p

Characterization of the N-Terminal Domain of BteA: A <em>Bordetella</em> Type III Secreted Cytotoxic Effector

<div><p>BteA, a 69-kDa cytotoxic protein, is a type III secretion system (T3SS) effector in the classical <em>Bordetella</em>, the etiological agents of pertussis and related mammalian respiratory diseases. Currently there is limited information regarding the structure of BteA or its subdomains, and no insight as to the identity of its eukaryotic partners(s) and their modes of interaction with BteA. The mechanisms that lead to BteA dependent cell death also remain elusive. The N-terminal domain of BteA is multifunctional, acting as a docking platform for its cognate chaperone (BtcA) in the bacterium, and targeting the protein to lipid raft microdomains within the eukaryotic host cell. In this study we describe the biochemical and biophysical characteristics of this domain (BteA287) and determine its architecture. We characterize BteA287 as being a soluble and highly stable domain which is rich in alpha helical content. Nuclear magnetic resonance (NMR) experiments combined with size exclusion and analytical ultracentrifugation measurements confirm these observations and reveal BteA287 to be monomeric in nature with a tendency to oligomerize at concentrations above 200 µM. Furthermore, diffusion-NMR demonstrated that the first 31 residues of BteA287 are responsible for the apparent aggregation behavior of BteA287. Light scattering analyses and small angle X-ray scattering experiments reveal a prolate ellipsoidal bi-pyramidal dumb-bell shape. Thus, our biophysical characterization is a first step towards structure determination of the BteA N-terminal domain.</p> </div

BteA contains two chaperon binding domains.

<p>(A) Sequence alignment of BteA's first 31 residues and the structurally-determined β-motif of SipA <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081557#pone.0081557-Lilic1" target="_blank">[6]</a> and ExoU <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081557#pone.0081557-Halavaty1" target="_blank">[7]</a>. Red numbers mark key residues of the β-motif as previously suggested. (B) SEC elution profiles of BteA32-287 (hatched grey line), BtcA∶BteA32-287 (red) and BtcA∶BteA287 (black). (C) Labeled BteA32-287 (red boxes) was mixed with serially diluted BtcA samples and the thermophoretic behavior was monitored at RT. Values were normalized to the fraction of bound receptor and are average of three independent experimental repeats. Values were fitted with logistic function and the denoted Kd values were extracted from the center of the curve.</p