In Silico Identification and in Vitro Analysis of B and T-Cell Epitopes of the Black Turtle Bean (Phaseolus Vulgaris L.) Lectin

Abstract

Background/aims: The incidence of lectin allergic disease is increasing in recent decades, and definitive treatment is still lacking. Identification of B and T-cell epitopes of allergen will be useful in understanding the allergen antibody responses as well as aiding in the development of new diagnostics and therapy regimens for lectin poisoning. In the current study, we mainly addressed these questions.

Methods: Three-dimensional structure of the lectin from black turtle bean (Phaseolus vulgaris L.) was modeled using the structural template of Phytohemagglutinin from P. vulgaris (PHA-E, PDB ID: 3wcs.1.A) with high identity. The B and T-cell epitopes were screened and identified by immunoinformatics and subsequently validated by ELISA, lymphocyte proliferation and cytokine profile analyses.

Results: Seven potential B-cell epitopes (B1 to B7) were identified by sequence and structure based methods, while three T-cell epitopes (T1 to T3) were identified by the predictions of binding score and inhibitory concentration. The epitope peptides were synthesized. Significant IgE binding capability was found in B-cell epitopes (B2, B5, B6 and B7) and T2 (a cryptic B-cell epitope). T1 and T2 induced significant lymphoproliferation, and the release of IL-4 and IL-5 cytokine confirmed the validity of T-cell epitope prediction. Abundant hydrophobic amino acids were found in B-cell epitope and T-cell epitope regions by amino acid analysis. Positively charged amino acids, such as His residue, might be more favored for B-cell epitope.

Conclusion: The present approach can be applied for the identification of epitopes in novel allergen proteins and thus for designing diagnostics and therapies in lectin allergy.

Keywords: Black turtle bean; Epitopes; In silico identification; Lectin; Peptide synthesis; QSAR.