HUMAN PAPILLOMAVIRUS TYPE-1 E4 PROTEIN IS A ZINC-BINDING PROTEIN

Study of the human papillomavirus (HPV) E4 gene product has focused la rgely on HPV type 1 (HPV 1) primarily because of the large quantities of protein that can be purified from HPV 1-induced warts. We have exte nded the characterization of the HPV 1 E4 protein and, in this study, have shown that protein purified from clinical material and a heterolo gous expression system contains the divalent metal ion zinc. Furthermo re, using a [Zn-65]Cl-2 dot-blot assay, we have shown that this bindin g is specific for zinc and those divalent cations that are known to st ructurally substitute zinc in metalloproteins. Mutational analysis has demonstrated that histidine amino acids (residues 56, 86, and 121), b ut not the cysteine residue (115), are essential for the zinc-binding activity of the E4 protein. Two assayable functions of E4 are dimeriza tion and the formation of E4/cytokeratin structures in cultured cells; however, neither activity is abrogated by the loss of zinc binding. ( C) 1994 Academic Press, Inc.