Structural features of cation transport ATPases.
Several cation transport ATPases, sharing the common feature of a phosphorylated intermediate in the process of ATP utilization, are compared with respect to their subunit composition and amino acid sequence. The main component of these enzymes is a polypeptide chain of MW slightly exceeding 100,000, comprising an extramembranous globular head which is connected through a stalk to a membrane-bound region. With reference to the Ca2+ ATPase of sarcoplasmic reticulum, it is proposed that the catalytic (ATP binding and phosphorylation) domain resides in the extramembranous globular head, while cation binding occurs in the membrane region. Therefore, these two functional domains are separated by a distance of approximately 50 A. Alignment of amino acid sequences reveals extensive homology in the isoforms of the same ATPases, but relatively little homology in different cation ATPases. On the other hand, all cation ATPases considered in this analysis retain a consensus sequence of high homology, spanning the distance between the phosphorylation site and the preceding transmembrane helix. It is proposed that this sequence provides long-range functional linkage between catalytic and cation-binding domains. Thereby, translocation of bound cation occurs through a channel formed by transmembrane helices linked to the phosphorylation site. Additional sequences at the carboxyl terminal provide regulatory domains in certain ATPases.
Inesi
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Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201.
Kirtley
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MR
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism; D016623:Ion Pumps; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism; D013329:Structure-Activity Relationship
D016623:Ion Pumps; D006180:Proton-Translocating ATPases; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase