The antigenic structure of HBsAg: study of the d/y subtype determinant by chemical modification and site directed mutagenesis

Construction of atomic models of full hepatitis B vaccine particles at different stages of maturation

Hepatitis B, one of the world's most common liver infections, is caused by the Hepatitis B Virus (HBV). Via the infected cells, this virus generates non pathogen particles with similar surface structures as those found in the full virus. These particles are used in a recombinant form (HBsAg) to produce efficient vaccines. The atomic structure of the HBsAg particles is currently unsolved, and the only existing structural data for the full particle were obtained by electronic microscopy with a maximum resolution of 12 Å. As many vaccines, HBsAg is a complex bio-system. This complexity results from numerous sources of heterogeneity, and traditional bio-immuno-chemistry analytic tools are often limited in their ability to fully describe the molecular surface or the particle. For the Hepatitis B vaccine particle (HBsAg), no atomic data are available so far. In this study, we used the principal well-known elements of HBsAg structure to reconstitute and model the full HBsAg particle assembly at a molecular level (protein assembly, particle formation and maturation). Full HBsAg particle atomic models were built based on an exhaustive experimental data review, amino acid sequence analysis, iterative threading modeling, and molecular dynamic approaches.

Subgenotypes and mutations in the s and polymerase genes of hepatitis B virus carriers in the West Bank, palestine

The mutation rate and genetic variability of hepatitis B virus (HBV) are crucial factors for efficient treatment and successful vaccination against HBV. Until today, genetic properties of this virus among the Palestinian population remain unknown. Therefore, we performed genetic analysis of the overlapping S and polymerase genes of HBV, isolated from 40 Palestinian patients' sera. All patients were HBsAg positive and presented with a viral load above 105 HBV genome copies/ml. The genotyping results of the S gene demonstrated that HBV D1 was detected in 90% of the samples representing the most prominent subgenotype among Palestinians carrying HBV. Various mutations existed within the S gene; in five patients four known escape mutations including the common G145R and D144E were found. Furthermore, a ratio of 4.25 of non-synonymous to synonymous mutations in the S gene indicated a strong selection pressure on the HBs antigen loops of HBV strains circulating in those Palestinian patients. Although all patients were treatment-naïve, with the exception of one, several mutations were found in the HBV polymerase gene, but none pointed to drug resistance. The study presented here is the first report to address subgenotypes and mutation analyses of HBV S and polymerase genes in Palestine.

Polymerase chain reaction can resolve some undefined cases of hepatitis B virus antigenic subtyping

HBsAg subtypes were defined by means of adsorbed polyclonal antisera; however, HBsAg subtyping is currently usually carried out with monoclonal antibodies (Mab). We developed a complementary subtyping method based on the polymerase chain reaction. Reference samples belonging to all known HBsAg subtypes could be detected and grouped into four different categories (ayw1/ayw4/ayr, ayw2/ayw3, adw2/adrq+/adrq-, adw4). Thirteen HBsAg-positive serum samples previously subtyped as ad by means of monoclonal antibodies fell into the adw2/adrq+/adrq- group, as well as 13 ay samples into the ayw2/ayw3 group. These results could be confirmed by means of reference polyclonal antisera in nine ad cases (all adw2) and in seven ay cases (all ayw3); the remaining seven were below the detection limit of the polyclonal assay. Four samples which were not recognized by any of the d/y subtype-specific Mab were shown to contain ayw2/ayw3 sequences. Only one contained sufficient HBsAg to be confirmed as ayw3 by means of reference antisera. Three of five sera showing simultaneous reactivity both for d and y-specific Mab were classified as adw4 by PCR, as was one by reference polyclonal antisera. The y-specific monoclonal antibody cross-reacted with the adw4 subtype. Single adw2 sequences were amplified in one of the remaining two cases, as well as single ayw2/ayw3 sequences in the other, suggesting that they showed true coexistence of two strains of different subtype, only one of which was in active replication state. It is concluded that the method described is useful in the solution of some undefined cases obtained with the monoclonal-based assays.

Allelic subtypic determinants of hepatitis B surface antigen (i and t) that are distinct from d/y or w/r

A monoclonal antibody (I-18) was raised against an enneapeptide representing amino acids 125 to 133 of the product of the S gene of hepatitis B virus DNA [S(125-133) segment] with a sequence of Thr-Ile-126-Pro-Ala-Gln-Gly-Thr-Ser-Met. Another monoclonal antibody (T-7) was raised against an S(125-133) segment in which Ile-126 was replaced by Thr-126. In a panel of 16 samples of hepatitis B surface antigen (HBsAg) with known S gene sequences, I-18 reacted with 5 with Ile-126. T-7 reacted with 10 HBsAg samples with Thr-126; it did not, however, react with the remaining one of subtype ayw with Thr-126 flanked by Met-125 and Thr-127. The two allelic subtypic determinants, specified by Ile-126 and Thr-126 and distinct from d/y or w/r, were named i and t after isoleucine and threonine, which regulate them. They were expressed in a mutually exclusive fashion in 216 (83%) of 260 HBsAg samples from asymptomatic carriers. They were not detected in 36 (14%) samples; the failure to detect an i or t determinant was particularly common in HBsAg samples of subtype ayw (26 [79%] of 33). A part of the S gene sequence was determined for eight HBsAg samples without a detectable i or t determinant. They had an Ile-126 or Thr-126 residue that was flanked by Thr-127, not the Pro-127 commonly possessed by HBsAg samples displaying an i or t determinant. Expression of the i/t allele, therefore, would require Pro-127. In eight (3%) of the samples, both i and t determinants were detected; the presence of i and t on the selfsame HBsAg particles was verified by sandwiching the particles between I-18 and T-7. A point mutation from thymine to cytosine at nucleotide 377 in the S gene, contributing different second letters to codon 126 (ATT for Ile and ACT for Thr), would have been responsible for the assembly of HBsAg particles with both i and t determinants by means of phenotypic mixing.