Identification of the 67-kDa Melittin-Like Proteins Interacting with Na⁺/K⁺-ATPase

Melittin, a peptide from bee venom, was found to interact with many proteins, including calmodulin target proteins and ion-transporting P-type ATPases. It is assumed that melittin mimics a protein module involved in protein-protein interactions within cells. Previously, a Na⁺/K⁺-ATPase containing the α1 isoform of the catalytic subunit was found to co-precipitate with a protein with a molecular weight of about 70 kDa that interacts with antibodies against melittin by cross immunoprecipitation. In the presence of a specific Na⁺/K⁺-ATPase inhibitor (ouabain), the amount of protein with a molecular weight of 70 kDa was increased in the precipitate. In order to identify melittin-like protein from murine kidney homogenate, a fraction of proteins (with a molecular mass of approximately 70 kDa) was obtained using affinity chromatography with immobilized antibodies specific to melittin. By mass spectrometry analysis, the obtained protein fraction was found to contain three molecular chaperones of Hsp70 superfamily: mtHsp70 (mortalin), Hsp73 and Grp78. These data suggest that chaperones from the Hsp70 superfamily contain a melittin-like module.