Glutathionylation of the Na K Pump

Abstract

Reversible oxidative modifications of proteins are of importance for the normal cell functioning, e.g. for the receptor-coupled signaling. The formation of a disulfide bond between a protein and a glutathione tripeptide (Glu-Cys-Gly,) is an oxidative, posttranslational modification that might be involved in the cellular signaling. Recently, the Cys46 residue of the sarcolemmal Na K ATPAse β1 subunit has been proposed as a target for glutathionylation. Here, we use all-atom Molecular Dynamics (MD) simulations to investigate structural consequences of the Cys46 glutathionylation in the E2P state of the protein. Being negatively charged at physiological pH, the glutathione modification can induce alterations similar to the effect of phosphorylation. In contrast with previous studies, we find that Cys46, buried deeply in the membrane, can be exposed to the cytosolic glutathione due to the defect and local rearrangement of the protein-membrane interface in the E2P state, rather than the β1 helix sliding outside the membrane, previously anticipated for the E1 state. These findings are in accord with the recent crystal structure of the E1P state of Na+, K+-ATPase, where the position of the β1 helix is essentially the same as it is in the E2P state. We will comment on the accessibility of glutathione to Cys46, which lies at the center of the membrane.