Determination of the electronic structure of proteins by quantum mechanics for discovery of new biological function

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With the aid of quantum mechanical calculations, we have explored the electronic structure of several proteins and obtained new insights about its relation with biological function. Membrane proteins such as the Kcsa potassium channel, the chloride channel, and the light-harvesting LH2 complex are characterized by very large dipole moments (500～1000 Debye). This means that the protein inside the membrane is strongly polarized. This polarization of charge is connected to biological function. For example, strong polarization may be useful to maintain constant the flux of ions through the membrane. Furthermore, the large dipole moment of these proteins is important on helpin smaller proteins like charybdotoxin to adopt the correct orientation when they interact with membrane proteins. Finally, the sulfilimine bond, a new type of chemical bonding inside proteins (collagen IV) has been investigated and its properties have been revealed using quantum mechanical calculations.