ABSTRACT
The 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 β1 and 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 use In Silico methods to analyze the physicochemical properties of the putative homophilic trans-dimer of β2 subunits and provide insights about the trans-dimerization interface stability. Our structural analysis predicts a molecular recognition mechanism of a trans-dimeric β2-β2 subunit and permits designing experiments that will shed light upon possible homophilic interactions of β2 subunits in the nervous system.
Author summary The adhesion molecule on glia (AMOG) is the β2 isoform 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 β1 isoform is a homophilic adhesion molecule in epithelia and therefore we hypothesized that β2 could also interact as a homophilic adhesion protein. In a previous work we show that fibroblasts (CHO) transfected with the human β2 subunit of the Na+-pump become adhesive. Moreover, protein-protein interaction assay in a co-culture of cells transfected with β2 tagged with two different markers (His6 and YFP) reveal a positive interaction between the β2-subunits. In the present work, we apply bioinformatics methods to analyze and discuss the formation of a trans-dimer of β2-subunits. Our In Silico study 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-β2 trans-dimer is different from that of the β1-β1 dimer; it involves different surfaces and therefore it explains why β-subunits can not form mixed (β1-β2) trans-dimers.
Competing Interest Statement
The authors have declared no competing interest.