A Homology Model Reveals Novel Structural Features and an Immunodominant Surface Loop/Opsonic Target in the Treponema pallidum BamA Ortholog TP_0326
| Autor: | Justin D. Radolf, Morgan LeDoyt, Amit Luthra, Melissa J. Caimano, Kelly L. Hawley, Adriana R. Cruz, Juan C. Salazar, Arvind Anand, Carson J. La Vake |
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| Rok vydání: | 2015 |
| Předmět: |
Molecular Sequence Data
Population Biology medicine.disease_cause Microbiology Protein Structure Secondary Epitope Bama medicine Animals Humans Amino Acid Sequence Syphilis Treponema pallidum Homology modeling education Molecular Biology Escherichia coli Peptide sequence education.field_of_study Treponema Immunodominant Epitopes Articles Opsonin Proteins biology.organism_classification Molecular biology Protein Structure Tertiary Rabbits Bacterial outer membrane Bacterial Outer Membrane Proteins |
| Zdroj: | Journal of Bacteriology. 197:1906-1920 |
| ISSN: | 1098-5530 0021-9193 |
| DOI: | 10.1128/jb.00086-15 |
| Popis: | We recently demonstrated that TP_0326 is a bona fide rare outer membrane protein (OMP) in Treponema pallidum and that it possesses characteristic BamA bipartite topology. Herein, we used immunofluorescence analysis (IFA) to show that only the β-barrel domain of TP_0326 contains surface-exposed epitopes in intact T. pallidum . Using the solved structure of Neisseria gonorrhoeae BamA, we generated a homology model of full-length TP_0326. Although the model predicts a typical BamA fold, the β-barrel harbors features not described in other BamAs. Structural modeling predicted that a dome comprised of three large extracellular loops, loop 4 (L4), L6, and L7, covers the barrel's extracellular opening. L4, the dome's major surface-accessible loop, contains mainly charged residues, while L7 is largely neutral and contains a polyserine tract in a two-tiered conformation. L6 projects into the β-barrel but lacks the VRGF/Y motif that anchors L6 within other BamAs. IFA and opsonophagocytosis assay revealed that L4 is surface exposed and an opsonic target. Consistent with B cell epitope predictions, immunoblotting and enzyme-linked immunosorbent assay (ELISA) confirmed that L4 is an immunodominant loop in T. pallidum -infected rabbits and humans with secondary syphilis. Antibody capture experiments using Escherichia coli expressing OM-localized TP_0326 as a T. pallidum surrogate further established the surface accessibility of L4. Lastly, we found that a naturally occurring substitution (Leu 593 → Gln 593 ) in the L4 sequences of T. pallidum strains affects antibody binding in sera from syphilitic patients. Ours is the first study to employ a “structure-to-pathogenesis” approach to map the surface topology of a T. pallidum OMP within the context of syphilitic infection. IMPORTANCE Previously, we reported that TP_0326 is a bona fide rare outer membrane protein (OMP) in Treponema pallidum and that it possesses the bipartite topology characteristic of a BamA ortholog. Using a homology model as a guide, we found that TP_0326 displays unique features which presumably relate to its function(s) in the biogenesis of T. pallidum 's unorthodox OM. The model also enabled us to identify an immunodominant epitope in a large extracellular loop that is both an opsonic target and subject to immune pressure in a human population. Ours is the first study to follow a structure-to-pathogenesis approach to map the surface topology of a T. pallidum rare OMP within the context of syphilitic infection. |
| Databáze: | OpenAIRE |
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