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Immunoreactive Protein Repertoires of Ehrlichia chaffeensis and E. canis Reveal the Dominance of Hypothetical Proteins and Conformation-dependent Antibody Epitopes. Infect Immun 2021; 89:e0022421. [PMID: 34370510 DOI: 10.1128/iai.00224-21] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The immunomes of Ehrlichia chaffeensis (E. ch.) and E. canis (E. ca.) have recently be revised to include immunodominant hypothetical proteins with conformational antibody epitopes. In this study, we examined 216 E. ch. and 190 E. ca. highly antigenic proteins according to ANTIGENpro and also performed a genome-wide hypothetical protein analysis (E. ch. n=104; E. ca. n=124) for immunoreactivity. Using cell-free protein expression and immunoanalysis, 118 E. ch. and 39 E. ca. proteins reacted with sera from naturally E. ch.-infected patients or E. ca.-infected dogs. Moreover, 22 E. ch. and 18 E. ca. proteins consistently and strongly reacted with a panel of patient or canine sera. A subset of E. ch. (n=18) and E. ca. (n=9) proteins were identified as immunodominant. Consistent with our previous study, most proteins were classified as hypothetical and the antibody epitopes exhibited complete or partial conformation-dependence. The majority (28/40; 70%) of E. ch. and E. ca. proteins contained transmembrane domains and 19 (48%) were predicted to be secreted effectors. The antigenic repertoires of E. ch. and E. ca. were mostly diverse and suggest that the immunomes of these closely related ehrlichiae are dominated by species-specific conformational antibody epitopes. This study reveals a significant group of previously undefined E. ch. and E. ca. antigens and reaffirms the importance of conformation-dependent epitopes as targets of anti-Ehrlichia immune responses. These findings substantially expand our understanding of host-Ehrlichia immune responses, advance efforts to define the molecular features of protective proteins and improve prospects for effective vaccines for the ehrlichioses.
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Ehrlichia chaffeensis and E. canis hypothetical protein immunoanalysis reveals small secreted immunodominant proteins and conformation-dependent antibody epitopes. NPJ Vaccines 2020; 5:85. [PMID: 32963815 PMCID: PMC7486380 DOI: 10.1038/s41541-020-00231-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Accepted: 08/12/2020] [Indexed: 01/05/2023] Open
Abstract
Immunomolecular characterization of Ehrlichia chaffeensis (E. ch.) and E. canis (E. ca.) has defined protein orthologs, including tandem repeat proteins (TRPs) that have immunodominant linear antibody epitopes. In this study, we combined bioinformatic analysis and cell-free protein expression to identify undiscovered immunoreactive E. ch. and E. ca. hypothetical proteins. Antigenicity of the E. ch. and E. ca. ORFeomes (n = 1105 and n = 925, respectively) was analyzed by the sequence-based prediction model ANTIGENpro, and we identified ~250 ORFs in each respective ORFeome as highly antigenic. The hypothetical proteins (E. ch. n = 93 and E. ca. n = 98) present in the top 250 antigenic ORFs were further investigated in this study. By ELISA, 46 E. ch. and 30 E. ca. IVTT-expressed hypothetical proteins reacted with antibodies in sera from naturally E. ch.-infected patients or E. ca.-infected dogs. Moreover, 15 E. ch. and 16 E. ca. proteins consistently reacted with a panel of sera from patients or dogs, including many that revealed the immunoreactivity of “gold standard” TRPs. Antibody epitopes in most (>70%) of these proteins exhibited partial or complete conformation-dependence. The majority (23/31; 74%) of the major immunoreactive proteins identified were small (≤250 aa), and 20/31 (65%) were predicted to be secreted effectors. Unlike the strong linear antibody epitopes previously identified in TRP and OMP orthologs, there were contrasting differences in the E. ch. and E. ca. antigenic repertoires, epitopes and ortholog immunoreactivity. This study reveals numerous previously undefined immunodominant and subdominant antigens, and illustrates the breadth, complexity, and diversity of immunoreactive proteins/epitopes in Ehrlichia.
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Guan HH, Yoshimura M, Chuankhayan P, Lin CC, Chen NC, Yang MC, Ismail A, Fun HK, Chen CJ. Crystal structure of an antigenic outer-membrane protein from Salmonella Typhi suggests a potential antigenic loop and an efflux mechanism. Sci Rep 2015; 5:16441. [PMID: 26563565 PMCID: PMC4643347 DOI: 10.1038/srep16441] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 10/14/2015] [Indexed: 11/09/2022] Open
Abstract
ST50, an outer-membrane component of the multi-drug efflux system from Salmonella enterica serovar Typhi, is an obligatory diagnostic antigen for typhoid fever. ST50 is an excellent and unique diagnostic antigen with 95% specificity and 90% sensitivity and is used in the commercial diagnosis test kit (TYPHIDOT(TM)). The crystal structure of ST50 at a resolution of 2.98 Å reveals a trimer that forms an α-helical tunnel and a β-barrel transmembrane channel traversing the periplasmic space and outer membrane. Structural investigations suggest significant conformational variations in the extracellular loop regions, especially extracellular loop 2. This is the location of the most plausible antibody-binding domain that could be used to target the design of new antigenic epitopes for the development of better diagnostics or drugs for the treatment of typhoid fever. A molecule of the detergent n-octyl-β-D-glucoside is observed in the D-cage, which comprises three sets of Asp361 and Asp371 residues at the periplasmic entrance. These structural insights suggest a possible substrate transport mechanism in which the substrate first binds at the periplasmic entrance of ST50 and subsequently, via iris-like structural movements to open the periplasmic end, penetrates the periplasmic domain for efflux pumping of molecules, including poisonous metabolites or xenobiotics, for excretion outside the pathogen.
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Affiliation(s)
- Hong-Hsiang Guan
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
| | - Masato Yoshimura
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
| | - Phimonphan Chuankhayan
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
| | - Chien-Chih Lin
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
| | - Nai-Chi Chen
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan.,Institute of Biotechnology, and University Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan City, 701, Taiwan
| | - Ming-Chi Yang
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
| | - Asma Ismail
- Institute for Research in Molecular Medicine, Universiti Sains Malaysia, Kelantan, Malaysia
| | - Hoong-Kun Fun
- Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh, 11451, Saudi Arabia.,X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
| | - Chun-Jung Chen
- Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan.,Institute of Biotechnology, and University Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan City, 701, Taiwan.,Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh, 11451, Saudi Arabia.,Department of Physics, National Tsing Hua University, Hsinchu, 30043, Taiwan
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