Number and Molecular Weights of Foot-and-Mouth Disease Virus Capsid Proteins and the Effects of Maleylation

Evidence was obtained by gel electrophoresis that foot-and-mouth disease virus (FMDV) type A(12) protein migrates mainly in a zone corresponding to polypeptide(s) approximately 25,000 daltons in molecular weight. Additional minor components were observed, four with molecular weights ranging from 10,000 to 22,500 daltons and one with a molecular weight of 37,500 daltons. The minor components comprised about 10% of the total protein and were present in variable amounts. The 75S empty capsids contained primarily 25,000-, 37,500- and 50,000-dalton zones. These molecular weights were estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate versus proteins of known molecular weight, including poliovirus and vesicular stomatitis virus proteins. Maleylation of the amino residues of FMDV protein solubilized it to about 5 to 10 mg/ml in aqueous, nondenaturing solvents. This permitted molecular weights to be estimated also by gel filtration. Maleylation of 70% of the available amino groups of the FMDV protein produced heat and sodium dodecyl sulfate-stable polymeric aggregates of 10 to 20% of the 25,000-dalton zone. It also resulted in an increase in the molecular weight of this zone by an amount equivalent (ca. 1,000) to that expected from the added maleyl residues.