Isolation and characterization of adenovirus Type 2 vertex capsomer (Penton Base)

Abstract

Using two temperature-sensitive mutants of human adenovirus 2, H 2 ts-115 and H 2 ts-125, both defective in fiber production at 39.5°, it was possible to isolate appreciable amounts of vertex capsomer (penton base) devoid of fiber projection. The penton base was purified by Freon extraction, ammonium sulfate precipitation, DEAE-Sephadex, and hydroxyapatite chromatography. The final product was homogeneous by two-dimensional immunoelectrophoresis, analytical ultracentrifugation, SDS-polyacrylamide gel electrophoresis, and electron microscopy. The penton base thus isolated had a sedimentation coefficient of 9.1 S and an apparent molecular weight of about 500, 000. Stoichiomeric analysis of the penton base and fiber components of adenovirion, performed by biochemical and immunological methods, suggested that there are five subunits of 85,000 daltons per penton base structure. This finding and the sedimentation data implied an elongated shape for the vertex capsomer. The penton base had an isoelectric point of 5.8. No free N-terminal amino acid was detectable and the amino acid composition showed a relatively high content of dicarboxylic amino acids, leucine, and significant amounts of cysteine. The penton base had a cell-detaching effect, but did not seem to induce neutralizing antibodies. No endonuclease activity was found associated with the purified penton base obtained after hydroxyapatite chromatography, or even after the DEAE-Sephadex step.