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. 2013 Nov;69(Pt 11):1196-201.
doi: 10.1107/S1744309113027371. Epub 2013 Oct 26.

Structure of CT584 from Chlamydia trachomatis refined to 3.05 Å resolution

Michael L Barta  1 , John Hickey, Kyle E Kemege, Scott Lovell, Kevin P Battaile, P Scott Hefty
Affiliations

Structure of CT584 from Chlamydia trachomatis refined to 3.05 Å resolution

Michael L Barta et al. Acta Crystallogr Sect F Struct Biol Cryst Commun. 2013 Nov.

Abstract

Chlamydia trachomatis is a major cause of various diseases, including blinding trachoma and pelvic inflammatory disease, and is the leading reported sexually transmitted bacterial infection worldwide. All pathogenic Chlamydiae spp. utilize a supramolecular syringe, or type III secretion system (T3SS), to inject proteins into their obligate host in order to propagate infection. Here, the structure of CT584, a T3SS-associated protein, that has been refined to a resolution of 3.05 Å is reported. The CT584 structure is a hexamer comprised of a trimer of dimers. The structure shares a high degree of similarity to the recently reported structure of an orthologous protein, Cpn0803, from Chlamydia pneumoniae, which highlights the highly conserved nature of this protein across these chlamydial species, despite different tissue tropism and disease pathology.

Keywords: CT584; Chlamydia trachomatis; type III secretion system.

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Figures

Figure 1
Figure 1
(a) Prismatic crystals of CT584 obtained from Hampton Natrix screen condition No. 27 upon in situ proteolysis with α-chymotrypsin. Crystals were obtained in 1–2 d. (b) Representative X-ray diffraction pattern of CT584 crystals at ϕ = 90°. The crystal was exposed for 0.2 s over a 0.2° oscillation range. The edges of the detector correspond to 1.65 Å in the x axis and 2.40 Å in the y axis.
Figure 2
Figure 2
Crystal structure of CT584 (residues Thr14–Thr180) refined to 3.05 Å resolution. (a) A single polypeptide is found in the asymmetric unit. The cartoon ribbon format is colored according to secondary structure, with α-helices in orange and β-strands in cyan. Loop regions that were unmodeled owing to poor electron density are represented by dashed lines and the solid arrow highlights the π-bulge. (b) OMIT F o − F c weighted electron-density map (contoured at 3.0σ, omitting residues 95–100 and 123–127), calculated using PHENIX (Adams et al., 2002, 2010 ▶), represented as an orange cage around the region highlighted (dashed lines) in (a). (c) Superposition of of CT584 (cyan) and Cpn0803 (purple). The calculated r.m.s.d. was 0.53 Å over 152/175 Cα atoms within 5.0 Å. The alignment is rotated 180° about the vertical axis with respect to (a). Cpn0803 terminal residues are labeled.
Figure 3
Figure 3
Dimerization of CT584. (a) The dimer interface as predicted by PISA is formed by a CT584 polypeptide in the asymmetric unit (orange) with a polypeptide related by a crystallographic twofold operator (cyan). (b) Amino-acid side chains relevant to dimer formation from each polypeptide are shown in ball-and-stick representation. Side chains are colored according to bonding interaction (red dashed line), with salt bridges in magenta and hydrogen bonds in lime. The backbone coloring is as in (a). The interface is highlighted in (a) (dashed lines) and is rotated 90° counterclockwise.
Figure 4
Figure 4
Oligomerization of CT584. (a) The hexamer interface as predicted by PISA is formed by six polypeptides related by a crystallographic twofold operator (dimer; Fig. 3 ▶) and by two crystallographic threefold operators of that dimer forming a trimer of dimers (hexamer). Each dimer pair is independently colored. (b) Amino-acid side chains relevant to dimer trimerization (hexamer) from each polypeptide dimer are shown in ball-and-stick representation. Side chains are colored according to bonding interactions (red dashed lines), with salt bridges in magenta and hydrogen bonds in cyan. The backbone coloring is as in (a). The interface is highlighted in (a) (solid arrow and dashed lines) and is rotated 90° clockwise about the vertical axis. (c) Proposed steps in the oligomerization of CT584. Each polypeptide is shown as a surface representation and colored as in (a).
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