Unidirectional Proton Transfer in an icosahedral viral capsid: A Proton Diode as external pH sensor

M.M. BRANDA; P.G. BELELLI; J. VISO; M.D. COSTABEL; D.M.A. GUÉRIN

Encuentro; II Meeting of the Spanish Network of Physical Virology; 2017

Experimental results obtaining with Triatoma Virus show that the capsid of this virus is stable at acidic conditions, but disassembles and releases the genome under alkaline environments. The hypothesis of the existence of an ion channel along the 5-fold symmetry axes in the capsid of small icosahedral viruses was postulated. Molecular Dynamic simulation showed that the presence of a Mg+2 cation at the 5-fold cavity allows the channel full hydration. Proton holes can move along the water wire following a Grotthuss-like mechanism. Under external alkaline conditions the transport is a concerted movement against the pH gradient. When the pH exterior is acidic, protons cannot traverse the water wire. The channel structure acts as a ´diode´ since permits protons only to exit but not to enter the capsid. These calculations are consistent with the observed TrV sensitivity to alkaline environments and resistance to acidic pHs. The putative metal ion at the 5-fold cavity would play a key role in the capsid mechanism for the pH sensing.