Purification and structural analysis of the hepatitis B virus preS1 expressed from Escherichia coli

The preS1 of hepatitis B virus (HBV) is located at the outermost part of the envelope protein and possesses several functionally important regions such as hepatocyte receptor-binding site and virus-neutralizing epitopes. As the first step to understand the structure-function relationship for the preS1 antigen, we have purified the preS1 and performed its structural characterization by circular dichroism (CD) spectroscopy. The preS1 was purified to near homogeneity from bacterially expressed glutathione S-transferase (GST)-preS1 fusion protein by two-step purification, affinity chromatography on glutathione-agarose column, and cation-exchange chromatography on Mono S column. The CD analysis showed that the purified preS1, which was largely unstructured in aqueous solution, acquired a significant (16%) alpha-helical structure when analyzed in 50% trifluoroethanol or 20 mM SDS. The results suggest that the preS1 assumes a mainly unstructured conformation and may form induced secondary structures upon binding to target proteins or under hydrophobic environment.

Fine mapping of virus-neutralizing epitopes on hepatitis B virus PreS1

We identified the epitopes on the preS1 which induce antibodies that neutralize both ad and ay subtypes of hepatitis B virus (HBV). Previously we generated murine monoclonal antibodies KR359 and KR127 that bind specifically to the preS1 of HBV. In this study we have performed fine mappings of the epitopes of the antibodies by examining their reactivity with GST fusion proteins, which contain a series of deletion mutants of the preS1. KR359 and KR127 specifically recognize aa 19-26 and 37-45 of the preS1, respectively. The antibodies neutralized both adr and ayw subtypes of the virus in an in vitro neutralization assay using in vitro infection of adult human hepatocyte primary culture by HBV. The epitopes showed little sequence divergence and the antibodies bound to the preS1 of all the HBV subtypes and variants tested.

Isolation and characterization of a novel antifungal peptide from Aspergillus niger

A novel antifungal peptide (termed as Anafp) was isolated from the culture supernatant of the filamentous fungi, Aspergillus niger. The whole amino acid sequence of Anafp was determined and the peptide was found to be composed of a single polypeptide chain with 58 amino acids including six cysteine residues. The peptide shows some degree of sequence homology to a cysteine-rich antifungal peptides reported from the seeds of Sinapis alba and Arabidopsis thaliana or the extracellular media of Aspergillus giganteus and Penicillium chrysogenumsome. Cysteine-spacing pattern of Anafp was similar to that of the antifungal peptide from Penicillium chrysogenum. The Anafp exhibited potent growth inhibitory activities against yeast strains as well as filamentous fungi at a range from 4 to 15 microM. In contrast, Anafp did not show antibacterial activity against Escherichia coli and Bacillus subtilis even at 50 microM.

A novel HLA-DR12 allele (DRB1*1206) found in a Korean B-cell line

At least 6 HLA-DRB1*12 alleles have been identified to date with nucleotide polymorphism occurring at codons 37, 57-58, 60, 67, 85 and 87. In this report, we describe the identification of another new HLA-DRB1*12 allele: DRB1*1206. This novel allele was found in an Epstein-Barr virus (EBV)-transformed Korean B-cell line "K-KT" having the HLA-phenotype A3, 24; B44, 61; Cw3; Bw4, 6; DR12, 13 during full-length cDNA isolation for cell line characterization and for production of HLA-DR recombinant proteins. The allele was identified initially by cycle sequencing of subcloned HLA-DRB full-length cDNA.

Reassembly and reconstitution of separate alpha and beta chains of human leukocyte antigen DR4 molecule isolated from Escherichia coli

The class II major histocompatibility complex molecules play a major role in presentation of exogenous antigenic peptides to the CD4 positive helper T cell. These are heterodimeric cell surface glycoproteins consisting of alpha- and beta-chains. In the present study, we cloned and expressed the alpha- and beta-chain of HLA-DR4 lacking the transmembrane and cytoplasmic domain separately in Escherichia coli using the pET-5a expression vector system. The expressed alpha- and beta-chains were purified in a denaturing condition by an ion exchange chromatography on Q-Sepharose and a gel filtration chromatography on Sephacryl S-200, respectively. The recombinant proteins were refolded and reassembled by removing the denaturing agent and concomitant reoxidation of the disulfide bond. The refolded heterodimeric rDR4 molecule was resolved by 12.5% SDS-PAGE in a nonreducing condition and confirmed by Western blot using polyclonal antibody against DR-alpha and the monoclonal antibody (L243) for the conformationally correct DR molecule. The rDR4 molecules were reconstituted with a 50-fold molar excess biot-HA (307-319), and the bound peptides to the heterodimer complex were determined by a microplate assay coated with L243 antibody using Extravidin-HRP conjugate.

On the unique structural organization of the Saccharomyces cerevisiae pyruvate dehydrogenase complex

Dihydrolipoamide acyltransferase (E2), a catalytic and structural component of the three functional classes of multienzyme complexes that catalyze the oxidative decarboxylation of alpha-keto acids, forms the central core to which the other components attach. We have determined the structures of the truncated 60-mer core dihydrolipoamide acetyltransferase (tE2) of the Saccharomyces cerevisiae pyruvate dehydrogenase complex and complexes of the tE2 core associated with a truncated binding protein (tBP), intact binding protein (BP), and the BP associated with its dihydrolipoamide dehydrogenase (BP.E3). The tE2 core is a pentagonal dodecahedron consisting of 20 cone-shaped trimers interconnected by 30 bridges. Previous studies have given rise to the generally accepted belief that the other components are bound on the outside of the E2 scaffold. However, this investigation shows that the 12 large openings in the tE2 core permit the entrance of tBP, BP, and BP.E3 into a large central cavity where the BP component apparently binds near the tip of the tE2 trimer. The bone-shaped E3 molecule is anchored inside the central cavity through its interaction with BP. One end of E3 has its catalytic site within the surface of the scaffold for interaction with other external catalytic domains. Though tE2 has 60 potential binding sites, it binds only about 30 copies of tBP, 15 of BP, and 12 of BP.E3. Thus, E2 is unusual in that the stoichiometry and arrangement of the tBP, BP, and E3.BP components are determined by the geometric constraints of the underlying scaffold.

Stoichiometry of binding of mature and truncated forms of the dihydrolipoamide dehydrogenase-binding protein to the dihydrolipoamide acetyltransferase core of the pyruvate dehydrogenase complex from Saccharomyces cerevisiae

The dihydrolipoamide dehydrogenase-binding protein (E3BP), a component of the Saccharomyces cerevisiae and mammalian pyruvate dehydrogenase (PDH) complexes, anchors an E3 homodimer inside each of the 12 pentagonal faces of the 60-mer dihydrolipoamide acetyltransferase (E2). To gain further insight into the number and localization of binding sites for E3BP on the 60-mer E2, truncated forms of the E3BP lacking the lipoyl and E3-binding domains were engineered by deletion mutagenesis. The recombinant proteins contained a polyhistidine extension on the amino terminus to facilitate purification to near-homogeneity. The stoichiometry of binding of the truncation mutants to a truncated form (inner core) of E2 (tE2, residues 181-454), lacking the lipoyl domain and the E1-binding domain, was determined. Mixtures containing tE2 and excess intact or truncated forms of E3BP were subjected to ultracentrifugation to separate the large complexes from unbound E3BP or tE3BP, and the complexes were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After staining with Coomassie brilliant blue and destaining, the gels were analyzed with a video area densitometer. The results showed that tE2 binds about 20 copies of intact E3BP-H, about 24 copies of tE3BP-H144 (residues 144-380), lacking the lipoyl domain, and about 31 copies of tE3BP-H218 (residues 218-380), lacking both the lipoyl and E3-binding domains. The results indicate that there apparently is a binding site for E3BP on each E2 subunit and that steric hindrance by segments of E3BP prevents full stoichiometric binding of E3BP to the pentagonal dodecahedron-like E2.

Expression, purification, and characterization of the dihydrolipoamide dehydrogenase-binding protein of the pyruvate dehydrogenase complex from Saccharomyces cerevisiae

Genes encoding dihydrolipoamide dehydrogenase (E3) and the E3-binding protein (E3BP, protein X), components of the Saccharomyces cerevisiae pyruvate dehydrogenase (PDH) complex, were coexpressed in Escherichia coli to produce an E3BP-E3 complex, thereby minimizing proteolysis of E3BP and facilitating its purification. The 2 genes were linked into a single transcriptional unit separated by a 31-nucleotide segment containing a ribosome-binding sequence. The E3BP-E3 complex was highly purified and then separated into E3 and E3BP by chromatography on hydroxylapatite in the presence of 5 M urea. The E3BP-E3 complex combined rapidly with a pyruvate dehydrogenase (E1)-dihydrolipoamide acetyltransferase (E2) subcomplex (E1-E2 subcomplex) to reconstitute a functional PDH complex, with pyruvate oxidation activity similar to that of PDH complex from bakers' yeast. The stoichiometry of binding of E3BP and E3BP-E3 complex to the 60-subunit pentagonal dodecahedron-like E2 was determined with a truncated form of E2 (tE2, residues 206-454) lacking the lipoyl domain and the E1-binding domain, and with E1-E2 subcomplex, which contains intact E2. Mixtures containing tE2 or E1-E2 subcomplex and excess E3BP or E3BP-E3 complex were subjected to ultracentrifugation to separate the large complexes from unbound E3BP or E3BP-E3, and the complexes were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After staining with Coomassie brilliant blue and destaining, the gels were analyzed with a video area densitometer. The results showed that the E1-E2 subcomplex binds about 12 E3BP monomers attached to 12 E3 homodimers. Similar results were obtained by analysis of highly purified PDH complex from bakers' yeast.(ABSTRACT TRUNCATED AT 250 WORDS)