Serological Reactivity and Biochemical Characterization of Methylated and Unmethylated Forms of a Recombinant Protein Fragment Derived from Outer Membrane Protein B of <i>Rickettsia typhi</i>
Bibliographic record
Abstract
Rickettsia typhi, an obligate intracellular bacterium that causes murine typhus, possesses a heavily methylated outer membrane protein B (OmpB) antigen. This immunodominant antigen is responsible for serological reactions and is capable of eliciting protective immune responses with a guinea pig model. Western blot analysis of partially digested OmpB with patient sera revealed that most of the reactive fragments are larger than 20 kDa. One of these fragments, which is located at the N terminus (amino acids 33 to 273), fragment A (At), has been expressed in Escherichia coli. The expressed protein (rAt) was purified by chromatography and properly refolded by sequential dialysis. The refolded rAt protein was recognized by at least 87% of the typhus group patient sera as determined by enzyme-linked immunosorbent assay (ELISA). However, the titers were lower than those obtained with OmpB of R. typhi. Since native OmpB is hypermethylated at lysine residues, we chemically methylated the lysine residues in rAt. The methylation was confirmed by amino acid composition analysis, and the methylation pattern of the methylated rAt (mrAt) protein was similar to that of native At from OmpB, as revealed by liquid chromatography-mass spectrometry analysis. Both rAt and mrAt were evaluated in an ELISA for their serological reactivity with patient sera. Among patient sera tested, 83% exhibited higher titers with mrAt than with rAt. These results suggest that rAt, with or without methylation, can potentially replace rickettsia-derived OmpB or whole-cell antigen for the diagnosis of R. typhi infection.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".