Backbone and sidechain resonance assignments and secondary structure of Scc4 from Chlamydia trachomatis
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Backbone and sidechain resonance assignments and secondary structure of Scc4 from Chlamydia trachomatis Thilini O. Ukwaththage1 · Marco Tonelli2 · Megan A. Macnaughtan1 Received: 20 March 2020 / Accepted: 23 June 2020 © Springer Nature B.V. 2020
Abstract Chlamydia trachomatis is an obligate intracellular bacterium that causes the most common sexually transmitted bacterial diseases in the world. With a biphasic developmental cycle, the bacteria utilize a type III secretion system (T3SS) to invade host cells as infectious elemental bodies, which then differentiate into actively dividing reticulate bodies. The regulation of the developmental cycle and the T3SS are linked by the bi-functional protein, specific Chlamydia chaperone 4 (Scc4). Scc4 is a class I T3SS chaperone forming a heterodimer with specific Chlamydia chaperone 1 (Scc1) to chaperone the essential virulence effector, Chlamydia outer membrane protein N. Scc4 also functions as a transcription factor by binding to the RNA polymerase holoenzyme between the flap region of the β subunit and region 4 of σ66. In order to investigate the mechanism behind Scc4’s dual functions and target its protein-protein interactions as a route for drug development, the structure and dynamics of Scc4 are being pursued. In the course of this effort, we assigned 89.2% of the backbone and sidechain 1 H, 15N, and 13C resonances of full-length Scc4. The assigned chemical shifts were used to predict the secondary structure and dynamic properties. The type and order of Scc4’s determined secondary structure are consistent with the X-ray crystal structures of other bacterial T3SS chaperones. Keywords Chlamydia trachomatis · Scc4 · Type III secretion system · Transcription regulation · RNAP binding protein · Chaperone
Biological context Scc41 was identified in Chlamydia trachomatis as a type III secretion system (T3SS) chaperone (Spaeth et al. 2009) and a transcription factor that directly binds the β subunit2 and the primary sigma factor, σ66,3 of the RNA polymerase holoenzyme (Rao et al. 2009). As a T3SS chaperone, Scc4 functions as an unusual heterodimer with Scc14 to chaperone CopN5 (Shen et al. 2015), an essential virulence factor that Electronic supplementary material The online version of this article (doi:https://doi.org/10.1007/s12104-020-09965-4) contains supplementary material, which is available to authorized users. * Megan A. Macnaughtan [email protected] 1
Department of Chemistry, Louisiana State University, Baton Range, LA 70803, USA
National Magnetic Resonance Facility at Madison and Biochemistry Department, University of Wisconsin- Madison, Madison, WI 53706, USA
2
interferes with the host’s microtubule network (Huang et al. 2008). The chaperone function of Scc4 occurs primarily in elemental bodies between the late stage of development and initiation of infection (when CopN is secreted into the host cell). The activity of Scc4 as a transcription factor occurs in reticulate bodies during the middle stage of development, when σ66-dependent transcr
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