Analysis of antigenic and conformational changes in hepatitis B surface antigen (HBsAg) identified in Iranian patients with chronic hepatitis B

Abstract

Background: The ‘a’ determinant domain of hepatitis B surface antigen (HBsAg) (positions 124 to 147) is recognized by antibodies raised either naturally or induced by vaccine. Failure to protect against hepatitis B virus (HBV) infection may occur due to the conformational changes of ‘a’ determinant induced by mutations. Objectives: The present study analyzed the molecular and three-dimensional (3D) characteristics of the HBsAg ‘a’ determinant mutations among Iranian chronic hepatitis B (CHB) patients, who were vaccine and drug naive. Methods: Eighty patients with HBsAg positive test results were selected according to the data extracted from questionnaires. Serologic and molecular assays were performed using real-time Polymerase Chain Reaction (PCR) and subsequently surface nested PCR on CHB patients. Next, an extensive mutational analysis was applied following direct sequencing on HBsAg amplified genes. The potential impacts of altered antigenic and 3D properties of amino acid substitutions were carried out using bioinformatics approaches. Results: All patients were negative for HBeAg and positive for anti-HBe. Mutational analysis showed that 60 (75%) of 80 patients had at least one amino acid substitution. Several mutations were found in ‘a’ determinant (P127L, P127T, G130N, andS136Y). Bioinformatics investigations indicated that all mutations induced a conformational change in ‘a’ determinant region. P127L substitution led to a considerable decreased HBsAg antigenicity compared to other mutants. Conclusions: The current analyses revealed that the studied mutations induced a local change in the ‘a’ determinant conformation. These findings could be useful for the design of HBsAg detection assays, which may significantly improve the ability to detect particular HBsAg mutants.