Charge transfer and polarization for chloride ions bound in ClC transport proteins: natural bond orbital and energy decomposition analyses.

摘要: ClC transport proteins show a distinct “broken-helix” architecture, in which certain α-helices are oriented with their N-terminal ends pointed toward the binding sites where chloride ions held extensively by backbone amide nitrogen atoms from helices. To understand effectiveness of such structures, we carried out natural bond orbital analysis and energy decomposition employing truncated active-site model systems for bound along translocation pore EcClC proteins. Our results indicated that stabilized environment electrostatic, polarization, charge-transfer interactions few side chains. Up to ∼25% formal charges were found smeared surroundings primarily via charge transfer chloride’s lone pair n(Cl) orbitals protein’s antibonding σ*(N–H) or σ*(O–H) orbitals; those σ* localized at polar N–H O–H bond...