Symmetric versus Asymmetric Features of Homologous Homodimeric Amine Oxidases: When Water and Cavities Make the Difference

Symmetry is an intrinsic property of homo-oligomers. Amine oxidases are multidomain homodimeric enzymes that contain one catalytic site per subunit, and that share a high homology degree. In this paper, we investigated, by fluorescence spectroscopy measurements, the conformational dynamics and resiliency in solutions of two amine oxidases, one from lentil seedlings, and one from Euphorbia characias latex, of which the crystallographic structure is still unknown. The data demonstrate that slight but significant differences exist at the level of the local tridimensional structure, which arise from the presence of large internal cavities, which are characterized by different hydration extents. Molecular dynamics and a contact network methodology were also used to further explore, in silico, the structural features of the two proteins. The analysis demonstrates that the two proteins show similar long-range symmetrical connectivities, but that they differ in their local (intra-subunit) contact networks, which appear mostly asymmetric. These features have been interpreted to suggest a new rationale for the functioning of amino oxidases as obligate homodimers.