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Chlamydia protein Pgp3 studied at high resolution in a new crystal form

DOI: 10.1107/S2052252518007637 DOI Help

Authors: Sahir Khurshid (Imperial College London) , Lata Govada (Imperial College London) , Gillian Wills (Imperial College London) , Myra O. Mcclure (Imperial College London) , John R. Helliwell (The University of Manchester) , Naomi E. Chayen (Imperial College London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Iucrj , VOL 5

State: Published (Approved)
Published: July 2018

Open Access Open Access

Abstract: The protein Pgp3 is implicated in the sexually transmitted disease chlamydia and comprises an extended complex arrangement of a C-terminal domain (CTD) and an N-terminal domain (NTD) linked by a triple-helix coiled coil (THCC). Here, the X-ray crystal structure of Pgp3 from an LGV1 strain is reported at the highest X-ray diffraction resolution obtained to date for the full protein. The protein was crystallized using a high concentration of potassium bromide, which resulted in a new crystal form with relatively low solvent content that diffracted to a resolution of 1.98 Å. The three-dimensional structure of this new crystal form is described and compared with those of other crystal forms, and the potassium bromide binding sites and the relevance to chlamydia isolates from around the globe are described. The crystal packing is apparently driven by the CTDs. Since the threefold axes of the THCC and NTD are not collinear with the threefold axis of a CTD, this naturally leads to disorder in the THCC and the portion of the NTD that does not directly interact with the CTD via crystal packing. The key avenue to resolving these oddities in the crystal structure analysis was a complete new analysis in space group P1 and determining the space group as P212121. This space-group assignment was that originally determined from the diffraction pattern but was perhaps complicated by translational noncrystallographic symmetry. This crystal structure of a three-domain multi-macromolecular complex with two misaligned threefold axes was a unique challenge and has not been encountered before. It is suggested that a specific intermolecular interaction, possibly of functional significance in receptor binding in chlamydia, might allow the design of a new chemotherapeutic agent against chlamydia.

Journal Keywords: chlamydia protein; Pgp3; crystallization; crystal form; protein structure; X-ray crystallography; structural biology; sexually transmitted diseases.

Subject Areas: Biology and Bio-materials, Medicine

Instruments: I04-Macromolecular Crystallography