A recombinant hepatitis B core antigen polypeptide with the protamine-like domain deleted self-assembles into capsid particles but fails to bind nucleic acids.
We have cloned in Escherichia coli both the complete core gene of hepatitis B virus and a truncated version of it, leading to the synthesis of high levels of a core-antigen-equivalent polypeptide (r-p22) and of an e-antigen-equivalent polypeptide (r-p16), respectively. We then compared the structural and antigenic properties of the two polypeptides, as well as their ability to bind viral nucleic acids. r-p16 was found to self-assemble into capsid-like particles that appeared similar, when observed under the electron microscope, to those formed by r-p22. In r-p16 particles, disulfide bonds linked the truncated polypeptides in dimers, assembled in the particle by noncovalent interactions. In r-p22 capsids, further disulfide bonds, conceivably involving the carboxy-terminal cysteines of r-p22 polypeptides, joined the dimers together, converting the structure into a covalently closed lattice. The protamine-like domain was at least partly exposed on the surface of r-p22 particles, since it was accessible to selective proteolysis. Finally, r-p22, but not r-p16, was shown to bind native and denatured DNA as well as RNA. Taken together, these results suggest that the protamine-like domain in core polypeptides is a nucleic acid-binding domain and is dispensable for the correct folding and assembly of amino-terminal and central regions.
Gallina
A
A
Istituto di Genetica, Biochimica ed Evoluzionistica Consiglio Nazionale delle Ricerche, Università di Pavia, Italy.
Bonelli
F
F
Zentilin
L
L
Rindi
G
G
Muttini
M
M
Milanesi
G
G
D002213:Capsid / Q000096:biosynthesis*; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005814:Genes, Viral; D006512:Hepatitis B Core Antigens / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D006513:Hepatitis B e Antigens / Q000032:analysis; D006515:Hepatitis B virus / Q000235:genetics*; D015151:Immunoblotting; D008970:Molecular Weight; D010957:Plasmids; D011479:Protamines; D011994:Recombinant Proteins / Q000032:analysis / Q000378:metabolism; D015678:Viral Structural Proteins / Q000235:genetics*
D006512:Hepatitis B Core Antigens; D006513:Hepatitis B e Antigens; D011479:Protamines; D011994:Recombinant Proteins; D015678:Viral Structural Proteins