PROSITE documentation PDOC00328

Sodium and potassium ATPases beta subunits signatures

The sodium pump (Na+,K+ ATPase), located in the plasma membrane of all animal cells [1], is an heterotrimer of a catalytic subunit (α chain), a glycoprotein subunit of about 34 Kd (β chain) and a small hydrophobic protein of about 6 Kd. The β subunit seems [2] to regulate, through the assembly of α/β heterodimers, the number of sodium pumps transported to the plasma membrane.

Structurally the β subunit is composed of a charged cytoplasmic domain of about 35 residues, followed by a transmembrane region, and a large extracellular domain that contains three disulfide bonds and glycosylation sites. This structure is schematically represented in the figure below.

                                +----+ +--+       +-----------+
                                |    | |  |       |           |
        xxxxxxxxxxxxxxxxxxxxxxxxCxxxxCxCxxCxxxxxxxCxxxxxxxxxxxCxxxx
           ****                      ****
        <-Cyt-><TM><------------Extracellular--------------------->

'C': conserved cysteine involved in a disulfide bond.
'*': position of the patterns.

Four isoforms of the β subunit (β-1 to β-4) are currently known.

Gastric (K+, H+) ATPase (proton pump) responsible for acid production in the stomach consist of two subunits [3]; the β chain is highly similar to the sodium pump β subunits.

We developed two signature patterns for β subunits. The first is located in the cytoplasmic domain, while the second is found in the extracellular domain and contains two of the cysteines involved in disulfide bonds.