Molecular cloning, bioinformatics analysis and functional characterization of B-cell activating factor in goat ( Capra hircus)

Abstract

B-cell activating factor of the TNF family (BAFF) induces B cell survival, proliferation, immunoglobulin secretion and has a role in enhancing immune responses. In the present study, we amplified the cDNA of goat ( Capra hircus) BAFF (designated gBAFF) from spleen by reverse transcription-PCR (RT-PCR). The open reading frame (ORF) of gBAFF covers 843 bp encoding 280 amino acids, with a 152-aa mature peptide. Sequence comparison indicated that the amino acid of gBAFF possessed the TNF signature, a transmembrane domain, a putative furin protease cleavage site and three cysteine residues. The predicted three-dimensional (3D) structure of the soluble part of gBAFF (gsBAFF) analyzed by “comparative protein modelling” revealed that it was very similar to its counterparts. Real-time quantitative PCR (qPCR) analysis indicated that gBAFF mRNA was predominantly expressed in goat lymphoid tissue spleen. Recombinant gsBAFF was fused with a small ubiquitin-related modifier (SUMO) gene to enhance the soluble expression level in Escherichia coli BL21 (DE3). The resulting fused protein SUMO-gsBAFF was efficiently expressed and purified using metal chelate affinity chromatography (Ni–NTA), then confirmed by SDS–PAGE and Western blotting analysis. In vitro, the MTT assays and flow cytometric analysis indicated that SUMO-gsBAFF as well as gsBAFF could promote the survival/proliferation of goat splenic B cells or mouse splenic B cells. Therefore, BAFF may be a potential immunologic factor for enhancing immunological efficacy in goat.