The electrostatic surface potential of Cj0843, SLT70, and LtgA.

<p>The electrostatic surface calculations were done using APBS [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197136#pone.0197136.ref041" target="_blank">41</a>], and two opposite views of the doughnut-shaped proteins are shown. The active site groove is indicated by an arrow and labeled ‘1’; the positively charged pocket 2 is indicated by a yellow ‘2’.</p

Data collection, structure solution, and refinement statistics for Cj0843 data sets.

<p>Data collection, structure solution, and refinement statistics for Cj0843 data sets.</p

Structural studies and molecular dynamics simulations suggest a processive mechanism of exolytic lytic transglycosylase from <i>Campylobacter jejuni</i>

<div><p>The bacterial soluble lytic transglycosylase (LT) breaks down the peptidoglycan (PG) layer during processes such as cell division. We present here crystal structures of the soluble LT Cj0843 from <i>Campylobacter jejuni</i> with and without bulgecin A inhibitor in the active site. Cj0843 has a doughnut shape similar but not identical to that of <i>E</i>. <i>coli</i> SLT70. The C-terminal catalytic domain is preceded by an L-domain, a large helical U-domain, a flexible linker, and a small N-terminal NU-domain. The flexible linker allows the NU-domain to reach over and complete the circular shape, using residues conserved in the Epsilonproteobacteria LT family. The inner surface of the Cj0843 doughnut is mostly positively charged including a pocket that has 8 Arg/Lys residues. Molecular dynamics simulations with PG strands revealed a potential functional role for this pocket in anchoring the negatively charged terminal tetrapeptide of the PG during several steps in the reaction including homing and aligning the PG strand for exolytic cleavage, and subsequent ratcheting of the PG strand to enhance processivity in degrading PG strands.</p></div

A proposed mechanism of PG hydrolysis by Cj0843.

<p>The colors of the domains of Cj0843 are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197136#pone.0197136.g001" target="_blank">Fig 1</a>. The 8 R/K residues in pocket 2 are indicated, and several additional R/K labels are drawn for illustrative purposes. In addition to E390 (black sphere), M410 and Y463 are labeled ‘M’ and ‘Y’, respectively. A narrowing of the active site groove is depicted in states 6–8 with an accompanying shift of the flanking NU-domain. The boat conformation of MurNAc-1 is drawn in state 6. The tetrapeptide sections of the 5 PG disaccharide units are colored as in Figures F and K in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197136#pone.0197136.s009" target="_blank">S9 Fig</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197136#pone.0197136.s015" target="_blank">S3 Video</a>.</p

Bulgecin A binding to Cj0843.

<p>A Unbiased |Fo|-|Fc| difference density contoured at 3σ contour level showing the presence of bulgecin A in the active site (bulgecin A was removed from the map calculations). Bulgecin A is depicted with carbon atoms colored in cyan. B Interactions of bulgecin A in the active site; interacting water molecules are shown as red spheres. Hydrogen bonds are depicted as dashed lines. C Active site movements of Cj0843 upon bulgecin A binding. The bulgecin A complex (cyan), apo Cj0843 P3₁21 structure (red), apo Cj0843 I23 structure (orange) are superimposed to highlight the main chain movements and the F412 side chain movement. The view is roughly 90° rotated from the view in A and depicts the active site groove from the side. Residues M410, Y463, and the catalytic E390 are shown in stick model.</p

The structure of soluble lytic transglycosylase of Cj0843.

<p>A Front view of Cj0843 depicting the NU domain (teal), NU-loop (magenta), U-domain (blue), UL-loop (blue-green), L domain (yellow), and C-domain (red). The disulfide bond between C87 and C102 is in green stick model, and the catalytic E390 is shown in black spheres. B Side view of Cj0843 (90 degrees rotated along a vertical axis relative to the orientation in A).</p