Detailed structural analysis of exposed domains of membrane‐bound Na⁺, K⁺‐ATPase A model of transmembrane arrangement

Abstract

Exposed regions of the a-and /3-subunits of membrane-bound Na+,K+-ATPase were in turn hydrolyzed with trypsin. Resistance of the p-subunit to proteolysis was shown to be due mainly to the presence of disulfide bridge(s) in the molecule. A model for the spatial organisation of the enzyme in the membrane was proposed on the basis of detailed structural analysis of extramembrane regions of both subunits.

Functional Properties of Na,K-ATPase, and Their Structural Implications, as Detected with Biophysical Techniques

“…The genes for the Na,KATPase have been cloned, including isoforms expressed in a variety of different tissues [51,59,71,83]. For the ␣-subunit, consisting of about 1,000 residues, a variety of experimental techniques [9,26,44,46,58,82] have demonstrated the existence of 10 transmembrane segments [45], with both N-and C-termini cytoplasmic.…”

“…3). We propose an adaptation of a model to explain an ordered binding sequence for the SR Ca-ATPase [1,42,62] based on an initial proposal of Menguy et al [71]. The ordered entry and side-by-side alignment of the two Ca 2+ ions was confirmed by the high resolution structure [91].…”

“…Hypothetical structure-function relation of the cytoplasmic ionbinding sites of the Na,K-ATPase. Binding of three Na + ions is proposed on the basis of a model for the SR-Ca-ATPase [71] as discussed in the text. The negatively charged amino acids D (aspartate) and E (glutamate) are placed according to a proposal of Vilsen et al [93].…”

Family of human Na+,K+‐ATPase genes Structure of the gene for the catalytic subunit (αIII‐form) and its relationship with structural features of the protein

“…Certain relations are traced when comparing the exon-intron structure of the analysed gene and the model for the transmembrane organization of the a-form of the Na+,K+-ATPase catalytic subunit based upon the data of limited proteolysis [27,28], immunochemical analysis [30] and differentiated fig.3. It should be noted that as a rule introns are situated between the regions of the regular structure or at their boundaries; however, e.g.…”

“…These regions designated in fig.2 22). Except for the two latter portions, others are in hydrophilic regions linking membrane segments II and III, IV and V. According to the structural model of the Na+,K+-ATPase catalytic subunit they are located in the cytoplasmic region of the enzyme [27,28]. Homologous portions 313-379, 495-524 and 678-775 include all the known components of the enzyme ATP-hydrolyzing site which are Asp-364, Lys-496, Asp-705, Asp-709 and Lys-714 in this sequence.…”