Biochemical and biophysical characterization of the RVB-1/RVB-2 protein complex, the RuvBL/RVB homologues in Neurospora crassa

The RVB proteins, composed of the conservative paralogs, RVB1 and RVB2, belong to the AAA+ (ATPases Associated with various cellular Activities) protein superfamily and are present in archaea and eukaryotes. The most distinct structural features are their ability to interact with each other forming the RVB1/2 complex and their participation in several macromolecular protein complexes leading them to be involved in many biological processes. We report here the biochemical and biophysical characterization of the Neurospora crassa RVB-1/RVB-2 complex. Chromatographic analyses revealed that the complex (APO) predominantly exists as a dimer in solution although hexamers were also observed. Nucleotides influence the oligomerization state, while ATP favors hexamers formation, ADP favors the formation of multimeric states, likely dodecamers, and the Molecular Dynamics (MD) simulations revealed the contribution of certain amino acid residues in the nucleotide stabilization. The complex binds to dsDNA fragments and exhibits ATPase activity, which is strongly enhanced in the presence of DNA. In addition, both GFP-fused proteins are predominantly nuclear, and their nuclear localization signals (NLS) interact with importin-α (NcIMPα). Our findings show that some properties are specific of the fungus proteins despite of their high identity to orthologous proteins. They are essential proteins in N. crassa, and the phenotypic defects exhibited by the heterokaryotic strains, mainly related to growth and development, indicate N. crassa as a promising organism to investigate additional biological and structural aspects of these proteins.