Abstract
ABSTRACTThe Na+,K+-ATPase is an electrogenic transmembrane pump located in the plasma membrane of all animal cells. It is a dimeric protein composed of α and β subunits and has a third regulatory subunit (γ) belonging to the FXYD family . This pump plays a key role in maintaining low concentration of sodium and high concentration of potassium intracellularly. The α subunit is the catalytic one while the β subunit is important for the occlusion of the K+ions and plays an essential role in trafficking of the functional αβ complex of Na+,K+-ATPase to the plasma membrane. Interestingly, the β1and β2(AMOG) isoforms of the β subunit, function as cell adhesion molecules in epithelial cells and astrocytes, respectively. Early experiments suggested a heterotypic adhesion for the β2. Recently, we reported a homotypic trans-interaction between β2-subunits expressed in CHO cells. In this work we useIn Silicomethods to analyze the physicochemical properties of the putative homophilic trans-dimer of β2subunits and provide insights about thetrans-dimerization interface stability. Our structural analysis predicts a molecular recognition mechanism of atrans-dimeric β2-β2subunit and permits designing experiments that will shed light upon possible homophilic interactions of β2subunits in the nervous system.Author summaryThe adhesion molecule on glia (AMOG) is the β2isoform of the β-subunit of the Na+-pump that is localized in the nervous system, specifically in astrocytes. It was shown that it mediates Neuron-Astrocyte interaction, promoting neurite outgrowth and migration during brain development. In recent years we have shown that the ubiquitous β1isoform is a homophilic adhesion molecule in epithelia and therefore we hypothesized that β2could also interact as a homophilic adhesion protein. In a previous work we show that fibroblasts (CHO) transfected with the human β2subunit of the Na+-pump become adhesive. Moreover, protein-protein interaction assay in a co-culture of cells transfected with β2tagged with two different markers (His6and YFP) reveal a positive interaction between the β2-subunits. In the present work, we apply bioinformatics methods to analyze and discuss the formation of atrans-dimer of β2-subunits. OurIn Silicostudy predicts a relatively stable dimer with an interface that involves the participation of four out of the seven N-glycosylation sites. Nevertheless, interacting interface and the dynamics of the β2-β2trans-dimer is different from that of the β1-β1dimer; it involves different surfaces and therefore it explains why β-subunits can not form mixed (β1-β2)trans-dimers.
Publisher
Cold Spring Harbor Laboratory