The reproductive importance of P-type ATPases

The nucleotide, inhibitor, and cation binding sites of P-type II ATPases

P-type ATPases constitute a ubiquitous superfamily of cation transport enzymes, responsible for carrying out actions of paramount importance in biology such as ion transport and expulsion of toxic ions from cells. The harmonized toggling of gates in the extra- and intracellular domains explain the phenomenon of specific cation binding in selective physiological states. A quantitative understanding of the fundamental aspects of ion transport mechanism and regulation of P-type ATPases requires detailed knowledge of thermodynamical, structural, and functional properties. Computational studies have made significant contributions to our understanding of biological ion pumps. Various 3D structures of Ca(2+) -ATPase between E1 and E2 transition states have given a impetus to the theorists to work on the Na(+) K(+) - and H(+) K(+) -ATPase to address important questions about their function. The current review delineates the importance of cation, nucleotide, and inhibitor binding domains, with a focus on the therapeutic potential and biological relevance of the three P-type II ATPases. This will give an insight into the ion selectivity and their conduction across the transmembrane helices of P-type II ATPases, which may pave the way to a range of fundamental questions about the mechanism and aid in the efforts of structure- and analog-based drug design.

Reanalysis of ATP11B, a type IV P-type ATPase

P-type ATPases are a venerable family of ATP-dependent ion transporters. Recently, evidence was presented that a rabbit gene in the type IV subfamily of P-type ATPases was missing a transmembrane helix (transmembrane domain 4) thought to be critical for ion transport, a deletion that would place the two major catalytic loops of the enzyme on opposite sides of the membrane. It was proposed that the resulting protein was a RING finger-binding protein that targets transcription factors to specific domains within the nucleus. From analysis of human genomic sequence data, it is shown here that the region containing transmembrane domain 4, corresponding to exon 12, is present in the human homolog of the gene, ATP11B. PCR analysis indicates that the predominant Atp11b transcripts in a rabbit cDNA library and in a mouse cDNA library also contain exon 12. The results suggest that the transcript proposed to encode the RING finger-binding protein is a minor rabbit-specific splice variant. The ATP11B gene thus may not encode a protein with a function radically different from that of other P-type ATPase transporters.