DFT, QTAIM, and NBO studies on the trimeric interactions in the protrusion domain of a piscine betanodavirus

Crystal structure of the protrusion domain (P-domain) of the grouper nervous necrosis virus (GNNV) shows the presence of three-fold trimeric protrusions with two asymmetrical calcium cations along the non-crystallographic three-fold axis. The trimeric interaction natures of the interacting residues and the calcium cations with the neighboring residues within the trimeric interface have been studied by the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses in the framework of the density-functional theory (DFT) approach. The results revealed that residues Leu259, Va1274, Trp280, and GIn322 of subunit A, Arg261, Asp275, A1a277, and Gln322 of subunit B, Leu259, Asp260, Arg261, A1a277, Va1278, and Leu324 of subunit C are the main residues involved in the trimeric interactions. Charge-dipole, dipole-dipole, and hydrogen bonding interactions make the significant contributions to these trimeric interactions. Among different interacting residues within trimeric interface, residue pair Arg261 B-Leu259C forms the strongest hydrogen bond inside the interface between subunits B and C. It was also found that calcium cations interact with residues Asp273, Va1274, and Asp275 of subunits A, B, and C through charge-charge and charge transfer interactions. (C) 2017 Elsevier Inc. All rights reserved.