Intrinsic disorder and oligomerization of the hepatitis delta virus antigen

The 195 amino acid basic protein (delta Ag) of hepatitis delta virus (HDV) is essential for replication of the HDV RNA genome. Numerous properties have been mapped to full-length delta Ag and attempts made to link these to secondary, tertiary and quaternary structures. Here, for the full-size delta Ag, extensive intrinsic disorder was predicted using PONDR-FIT, a meta-predictor of intrinsic disorder, and evidenced by circular dichroism measurements. Most delta Ag amino acids are in disordered configurations with no more than 30% adopting an alpha-helical structure. In addition, dynamic light scattering studies indicated that purified delta Ag assembled into structures of as large as dodecamers. Cross-linking followed by denaturing polyacrylamide gel electrophoresis revealed hexamers to octamers for this purified delta Ag and at least this size for delta Ag found in virus-like particles. Oligomers of purified delta Ag were resistant to elevated NaCl and urea concentrations, and bound without specificity to RNA and single- and double-stranded DNAs. (C) 2010 Elsevier Inc. All rights reserved.