The antigenic domain 1 of human cytomegalovirus glycoprotein B contains an intramolecular disulphide bond.

Glycoprotein B (gB, gpUL55) is the major antigen recognized by the neutralizing humoral immune response against human cytomegalovirus (HCMV). The immunodominant region on gB is the antigenic domain 1 (AD-1), a complex structure that requires a minimal continuous sequence of more than 75 amino acids (aa 552-635) for antibody binding. In this study, the structural requirements for antibody binding to AD-1 have been determined. The domain was expressed in prokaryotic and eukaryotic systems and analysed in immunoblots under reducing and non-reducing conditions. In addition, AD-1 was purified in an immunologically active form and the concentration of sulphydryl groups was determined. The data clearly show that the only form that is recognized by antibodies is a disulphide-linked monomer of AD-1. The disulphide bond is formed between cysteines at amino acid positions 573 and 610 of gB.