Cloning a truncated fragment (stx2a(1)) of the shiga-like toxin 2A (1) subunit of EHEC O157:H7: candidate immunogen for a subunit vaccine.

Shiga toxins consist of enzymatically active A and B subunit multimers. The A subunit of shiga-like toxins can be proteolytically cleaved into two parts, A(1) and A(2), with A(1) being responsible for toxic activity. Antibody neutralizing the A(1) subunit of shiga toxin may protect against infection of the enterohemorrhagic Escherichia coli (EHEC O157:H7). It was difficult to express the full-length A(1) subunit of shiga toxin 2 (stx2A(1)) in a previous study. We have now analyzed the full-length of stx2A(1) using bioinformatics software. The data show that the carboxyl terminal (of ~15 amino-acid residues) has strong hydrophobicity and low antigenicity. We cloned and expressed a truncated fragment of stx2A(1) (15 amino-acid residues of the carboxyl terminal being removed), designated stx2a(1), which can evoke a humoral immune response. Anti-Stx2a(1) antibodies can neutralize the native shiga toxin 2 both in vivo and in vitro, which suggests that Stx2a(1) serves as a candidate immunogen for a subunit vaccine that can also be used as the antigen to screen phage anti-shiga toxin antibody libraries.