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E5 transforming proteins of papillomaviruses do not disturb the activity of the vacuolar H⁺-ATPase

CRC Beatson Laboratories, Beatson Institute for Cancer Research, Switchback Road, Garscube Estate, Bearsden, Glasgow G61 1BD, UK¹

Author for correspondence: Malcolm Finbow. Present address: Department of Biological and Biomedical Sciences, Glasgow Caledonian University, Cowcaddens, Glasgow G4 0BA, UK. Fax +44 141 331 3208. e-mail M.Finbow{at}gcal.ac.uk

Papillomaviruses contain a gene, E5, that encodes a short hydrophobic polypeptide that has transforming activity. E5 proteins bind to the 16 kDa subunit c (proteolipid) of the eukaryotic vacuolar H⁺-ATPase (V-ATPase) and this binding is thought to disturb the V-ATPase and to be part of transformation. This link has been examined in the yeast Saccharomyces cerevisiae. The E5 proteins from human papillomavirus (HPV) type 16, bovine papillomavirus (BPV) type 1, BPV-4 E5 and various mutants of E5 and the p12' polypeptide from human T-lymphotropic virus (HTLV) type I all bound to the S. cerevisiae subunit c (Vma3p) and could be found in vacuolar membranes. However, none affected the activity of the V-ATPase. In contrast, a dominant-negative mutant of Vma3p (E137G) inactivated the enzyme and gave the characteristic VMA phenotype. A hybrid V-ATPase containing a subunit c from Norway lobster also showed no disruption. Sedimentation showed that HPV-16 E5 was not part of the active V-ATPase. It is concluded that the binding of E5 and E5-related proteins to subunit c does not affect V-ATPase activity or function and it is proposed that the binding may be due to a chaperone function of subunit c.

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				G. L. Disbrow, J. A. Hanover, and R. Schlegel Endoplasmic Reticulum-Localized Human Papillomavirus Type 16 E5 Protein Alters Endosomal pH but Not trans-Golgi pH J. Virol., May 1, 2005; 79(9): 5839 - 5846. [Abstract] [Full Text] [PDF]