The protein solubilized from the proteinic crystalline structure surrounding the granulosis virus of Trichoplusia ni by use of a carbonate buffer (pH 10.7) gives a major component, as analyzed by ultracentrifugation, with a molecular weight of 180,000. This protein has heterogeneous subunit structure as demonstrated by estimates of molecular weights by use of gel electrophoresis, amino-, and carboxy-terminal analyses, and peptide mapping of enzyme digests of the protein. The amino acid composition shows that the protein is acidic with a high percentage of amino acids with hydrophobic side groups. Optical rotatory dispersion studies reveal the presence of beta-structure in the protein complex. The conversion of the beta-structure to alpha-helix with sodium lauryl sulfate and to a random coil state with strong alkaline treatment are observed.