Human leukocyte interferon: relationship between molecular structure and species specificity

Human leukocyte interferon can be separated into two classes of subspecies by polynucleotide-agarose affinity chromatography; 30-40% of the molecular species have the polynucleotide-binding property and 60-70% lack affinity for the polynucleotide ligand. When analyzed on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, the former class of interferon has a slower mobility corresponding to the migration of a polypeptide of 21,000 daltons, while the latter class has a faster mobility corresponding to a polypeptide of 13,500-15,000 daltons. By analogy to the behavior of other interferons and a class of nucleotidyl transferases on the polynucleotide-agarose chromatography, we suggest that the human leukocyte interferon having the polynucleotide-binding site is in a possibly "native" conformation and the loss of affinity for polynucleotide results from a degradative alteration of the native molecules. Moreover, the alteration of interferon is accompanied by an increase in heterospecific activity on bovine cells. It is suggested that the polypeptide domain responsible for species specificity may be closely related to the polynucleotide binding area. The modified interferon molecule, however, still conserves its antiviral activity. The simplicity and the high capacity of polynucleotide-agarose chromatography make this a powerful technique for the purification of interferon. The easy separation of these two classes of human leukocyte interferon makes the purification procedures more rational and will facilitate the preparation of both subspecies to a high degree of molecular homogeneity.