Role of ATP hydrolysis in the DNA translocase activity of the bovine papillomavirus (BPV-1) E1 helicase

Abstract

The E1 protein of bovine papillomavirus type-1 is the viral replication initiator protein and replicative helicase. Here we show that the C-terminal ∼300 amino acids of E1, that share homology with members of helicase superfamily 3 (SF3), can act as an autonomous helicase. E1 is monomeric in the absence of ATP but assembles into hexamers in the presence of ATP, single-stranded DNA (ssDNA) or both. A 16 base sequence is the minimum for efficient hexamerization, although the complex protects ∼30 bases from nuclease digestion, supporting the notion that the DNA is bound within the protein complex. In the absence of ATP, or in the presence of ADP or the non-hydrolysable ATP analogue AMP-PNP, the interaction with short ssDNA oligonucleotides is exceptionally tight (T1/2 > 6 h). However, in the presence of ATP, the interaction with DNA is destabilized (T1/2 ∼60 s). These results suggest that during the ATP hydrolysis cycle an internal DNA-binding site oscillates from a high to a low-affinity state, while protein-protein interactions switch from low to high affinity. This reciprocal change in protein-protein and protein-DNA affinities could be part of a mechanism for tethering the protein to its substrate while unidirectional movement along DNA proceeds. © Copyright 2006 Oxford University Press.