M Noah

The precore/core gene of hepatitis B virus directs the synthesis of two polypeptides, the 21-kilodalton subunit (p21c) forming the viral nucleocapsid (serologically defined as core antigen [HBcAg]) and a secreted processed protein (p17e, serologically defined as HBe antigen [HBeAg]). Although most of their primary amino acid sequences are identical, HBcAg and HBeAg display different antigenic properties that are widely used in hepatitis B virus diagnosis. To locate and to characterize the corresponding determinants, segments of the core gene were expressed in Escherichia coli and probed with a panel of polyclonal or monoclonal antibodies in radioimmunoassays or enzyme-linked immunosorbent assays, Western blots, and competition assays. Three distinct major determinants were characterized. The single conformational determinant responsible for HBc antigenicity in the assembled core (HBc) and a linear HBe-related determinant (HBe1) were both mapped to an overlapping hydrophilic sequence around amino acid 80; a second HBe determinant (HBe2) was assigned to a location in the vicinity of amino acid 138 but found to require for its antigenicity the intramolecular participation of the extended sequence between amino acids 10 and 140. It is postulated that HBcAg and HBeAg share common basic three-dimensional structure exposing the common linear determinant HBe1 but that they differ in the presentation of two conformational determinants that are either introduced (HBc) or masked (HBe2) in the assembled core. The simultaneous presentation of HBe1 and HBc, two distinctly different antigenic determinants with overlapping amino acid sequences, is interpreted to indicate the presence of slightly differently folded, stable conformational states of p21c in the hepatitis B virus nucleocapsid.

Eight ribosomal proteins, L9, L11, L15, L17, L18, L19, L23, and L29, have been localized on the surface of the 50S subunit from Escherichia coli by immunoelectron microscopy. The specificity of the antibody binding site was demonstrated by stringent absorption experiments. For each protein, the antibody attachment site was localized on the two characteristic views of the 50S subunit. Thus, each protein could be located in a confined region on the three-dimensional structural model of the 50S subunit.

Ribosomes from three previously described mutants of Escherichia coli lacking L11 ( AM68 , AM76 , and AM77 ) supported in vitro termination with release factor 1 very poorly, but with release factor 2 had a severalfold elevation in activity for this function compared with ribosomes from a control strain or from a mutant containing unmethylated L11. L11 exerts its effect on the binding of the factors into a functional ribosomal complex with the termination codon. Reconstitution of L11 back into the L11-lacking ribosomes restored them to the control phenotype. The NH2-terminal part of L11 (amino acids 1-64) seems critical in modulating release factor binding. This part of L11 has been localized with the use of fragment-specific antibodies on the three-dimensional model of the 50 S subunit in the region from where the L7/L12 stalk originates. IgG antibodies from an antiserum specific for this fragment but not a middle fragment of L11 (amino acids 65-102) strongly inhibited in vitro termination. The activities of the two factors were inhibited differentially by several anti-L11 preparations recognizing antigenic determinants in the NH2-terminal part of L11. In all but one case, release factor 1 was more sensitive. These studies indicate that there are significant differences in the binding domains for the two release factors which are affected by the NH2-terminal part of L11.

In clinical practice, venous thromboembolic complications are much more frequent than bleeding disorders. In fact, disturbances within the protein C pathway due to coagulation factor V (FV) Leiden mutation and deficiency of protein C or protein S are the most frequent abnormalities in hereditary thrombophilia. Furthermore, acquired dysfunctions of the protein C system may predispose the single individual to an increased thrombotic risk. A routine-suited screening assay that would allow the monitoring of the proper interplay of factors in the protein C pathway could add an important factor to the basic coagulation profile. This consists of the prothrombin time and of the activated partial thromboplastin time, which currently allow only a screening for increased risk for bleeding but not for venous thromboembolism. A new functional screening test for the protein C system such as the presented ProC Global should therefore facilitate detection of FV Leiden as well as deficiency of protein C and protein S. The results of the present evaluation indicate that ProC Global is highly sensitive to activated protein C resistance/FV Leiden (100%) and protein C deficiency (90%) and sensitive to protein S deficiency (63%). Furthermore, the assay gives a quantitative measure of the net potential of the protein C pathway in relation to the intrinsic procoagulant system. The use of this assay for a prospective assessment of thromboembolic risk is the subject of current studies.