The family of human Na+,K+-ATPase genes. A partial nucleotide sequence related to the alpha-subunit

Methylcobalamin: coenzyme M methyltransferase isoenzymes MtaA and MtbA from Methanosarcina barkeri. Cloning, sequencing and differential transcription of the encoding genes, and functional overexpression of the mtaA gene in Escherichia coli

Methanosarcina barkeri is known to contain two methyltransferase isoenzymes, here designated MtaA and MtbA, which catalyze the formation of methyl-coenzyme M from methylcobalamin and coenzyme M. The genes encoding the two soluble 34-kDa proteins have been cloned and sequenced. mtaA and mtbA wee found to be located in different parts of the genome, each forming a monocystronic transcription unit. Northern blot analysis revealed that mtaA is preferentially transcribed when M. barkeri is grown on methanol and the mtbA gene when the organism is grown on H2/CO2 or trimethylamine. Comparison of the deduced amino acid sequences revealed the sequences of the two isoenzymes to be 37% identical. Both isoenzymes showed sequence similarity to uroporphyrinogen III decarboxylase from Escherichia coli. The mtaA gene was tagged with a sequence encoding six His placed bp before the mtaA start codon, and was functionally overexpressed in E. coli. 25% of the E. coli protein was found to be active methyltransferase which could be purified in two steps to apparent homogeneity with a 70% yield.

Cloning and characterization of the entire cDNA encoded by ATP1AL1--a member of the human Na,K/H,K-ATPase gene family

The cDNA for ATP1AL1--the fifth member of the human Na,K-/H,K-ATPase gene family--was cloned and sequenced. The deduced primary ATP1AL1 translation product is 1,039 amino acids in length and has Mr of 114,543. The encoded protein has all of the structural features common to known catalytic subunits of P-type membrane ion-transporting ATPases and is equally distant (63-64% of identity) from the Na,K-ATPase isoforms and the gastric H,K-ATPase. The ATP1AL1 encoded protein was proposed to represent a new separate group within the family of human potassium-dependent ion pumps.

Heterogeneity of ouabain binding sites in Schistosoma mansoni. First evidence for the presence of two (Na+ + K+)-ATPase isoforms in platyhelminths

Binding experiments with [3H]ouabain were performed to investigate the presence of (Na+ + K+)-ATPase (EC3.6.1.3) isoforms in adult male Schistosoma mansoni, the trematode responsible for human schistosomiasis. Non-linear regression analysis of equilibrium experiments performed with homogenates in a Mg-Pi medium indicated the presence of about 10% (Bmax = 223 +/- 67 fmol/mg protein) high-affinity sites (KD = 0.285 +/- 0.045 microM) and 90% (Bmax = 2117 +/- 348 fmol/mg protein) sites with a 20-fold lower affinity (KD = 4.9 +/- 1.28 microM). This was confirmed by their-exponential decay of [3H]ouabain dissociation. Furthermore, determination of association and dissociation rate constants indicated that the two classes of binding sites differed by their dissociation rate constants for ouabain (k-1 = 0.0185 +/- 0.0019 min-1 and 0.0997 +/- 0.0528 min-1 for high- and low-affinity sites, respectively). Surprisingly, the association rate constant measured for ouabain binding to S. mansoni homogenate (0.038 microM-1.min-1) was lower (25- to 80-fold) than the one usually observed for mammalian enzymes. This is the first direct evidence for the existence of (Na+ + K+)-ATPase isoforms in platyhelminths, invertebrates of great importance from the phylogenetic point of view.

Na,K-ATPase of cultured bovine lens epithelial cells: H2O2 effects

Na,K-ATPase function was studied in cultured bovine lens epithelial cells under confluent and non-confluent conditions. The affinity of the Na,K-ATPase for the cardiac glycoside, ouabain, differs between the confluent and non-confluent cultures. The confluent cells have a higher affinity for ouabain than do the non-confluent cells. The ouabain affinity of the confluent cells is similar to that for the Na,K-ATPase isolated from the bovine axolemma and the bovine lens cortex. The ouabain affinity of the non-confluent cells is similar to that for the Na,K-ATPase of the renal medulla and bovine lens epithelium. Similar results are not found with confluent and non-confluent MDCK cells. H2O2 treatment of confluent and non-confluent lens epithelial cell cultures has differing effects on the Na,K-ATPase function. In the confluent cell preparations, H2O2 affects K(+)-dependent dephosphorylation of the intermediate phosphoenzyme. In the non-confluent preparations. H2O2 appears to inhibit K(+)-occlusion.

Control region and gastric specific transcription of the rat H+,K(+)-ATPase alpha subunit gene

The rat gastric H+,K(+)-ATPase alpha subunit gene was cloned and the nucleotide sequence of its 5'-upstream region was determined. Sequence comparison with the corresponding part of the human gene indicated the presence of highly conserved regions which may be important for specific transcription of the alpha subunit in gastric parietal cells. The amino-terminal sequence (Met-Gly-Lys-Ala-Glu-) of the rat enzyme was similar to those of the pig and human enzymes. The gene organization of the rat enzyme was also similar to that of the human gene: introns 1, 2 and 9 were located in exactly the same positions as those in the human gene, and, as in the latter, exon 6 was not separated by an intron. The sequences of introns 1 and 2 were highly conserved among the rat, human and pig genes, but were entirely different from those of Na+,K(+)-ATPase catalytic subunit genes. Northern blot hybridization indicated that the gene was transcribed only in gastric mucosa.

The family of human Na,K-ATPase genes. ATP1AL1 gene is transcriptionally competent and probably encodes the related ion transport ATPase

The multigene family of human Na,K-ATPase is composed of 5 alpha-subunit genes, 3 of which were shown to encode the functionally active alpha 1, alpha 2 and alpha 3 isoforms of the catalytic subunits. This report describes the isolation, mapping and partial sequencing of the fourth gene (ATP1AL1) that was demonstrated here to be functionally active and expressed in human brain and kidney. Limited DNA sequencing of the ATP1AL1 exons allowed one to suggest that the gene probably encodes a new ion transport ATPase rather than an isoform of the Na,K-ATPase or the closely related H,K-ATPase.

The genes of Na,K-ATPase, a selfreview

The review is devoted to analysis of research carried out in the author's laboratory on structure-function relationships in genes coding for Na,K-ATPases. Also considered are problems related to molecular evolution of ion-transporting ATPases. This brief review is devoted to a fragment of research carried out in my laboratory, the Laboratory of Human Genes Structure and Function at the Shemyakin Institute of Bioorganic Chemistry, USSR Academy of Sciences. The area of the review may be named as structural-evolutionary analysis of functional anatomies of genes. The approach is fairly standard and its essence was formulated long ago: evolution decides 'to be or not to be' based on usefulness or lack of it. The elements of genes that are important for the gene function are retained in the course of evolution, and a comparison of genes having similar functions in different species should, hopefully, reveal different behavior of gene blocks, conservation of functionally significant blocks and variability of less significant or insignificant ones. An approach like this has been widely used in comparing proteins. However, a study of genes gives the investigator yet another tool of structural and evolutionary import: the exon structure may be relevant to the gene's evolutionary history, with exons corresponding to the functional domains (arguments for and against this fascinating hypothesis have been reviewed by Blake (Blake, 1985). However, even if the exon-domain correlation does not hold in the general case, a similarity in the exon-intron pattern of genes from different species is indicative of their common evolutionary origin and is enforcing the logic of variability analysis, provided, of course, that the compared genes have a common predecessor. A few years ago we employed this approach to analyze the functional structure of genes coding for subunits of bacterial DNA-dependent RNA polymerases and constructed functional maps of the enzyme. After that, a similar study of Na,K-ATPase genes to be reviewed here was started. The entire project became possible through collaboration with the lab of Dr. N. N. Modyanov, an eminent specialist in protein chemistry who had already accumulated considerable information on Na,K-ATPase from pig kidneys by that time. I would also like to stress that the work has been started on the initiative of the deceased Director of the Institute, Yu. A. Ovchinnikov. Since this is a self-review, I am asking my colleagues whose work will not be cited here to excuse me.(ABSTRACT TRUNCATED AT 400 WORDS)

Stability of Na(+)-K(+)-ATPase alpha-subunit isoforms in evolution

Encoding DNA for alpha 2- and alpha 3-isoforms of the alpha-subunit of the chicken Na(+)-K(+)-ATPase have been cloned, and their nucleotide sequences and deduced amino acid sequences are reported. Comparisons between these data and comparable data for the rat alpha-subunit isoforms make possible an assessment of alpha-subunit isoform diversity among vertebrates. There is approximately twice as much amino acid sequence difference between alpha-isoforms within a single species as there is difference between corresponding alpha-isoforms of bird and mammal. These data are consistent with triplication of the alpha-subunit gene and evolution of substantially different alpha-subunit isoforms before the separation of avian and mammalian lineages over 200 million years ago and then retention of the majority of these structural differences through subsequent evolution. The implications of this conversation of isoform-specific structural features are discussed in terms of transport functions and bioregulation of the Na(+)-K(+)-ATPase.

Human Na+,K+-ATPase genes. Beta-subunit gene family contains at least one gene and one pseudogene

The existence of a chromosome gene family containing at least one gene and one pseudogene was shown for the Na+,K+-ATPase beta-subunit. A partial structure of the beta 1-gene was determined, the coding part of which was completely homologous to cDNA of the Na+,K+-ATPase beta I-subunit from HeLa cells. The region encoding the putative protein transmembrane domain was shown to be bordered by two introns. The structure of a pseudogene (beta psi) was determined. This pseudogene is processed and contains multiple stop codons. Its homology to the beta I-subunit cDNA from HeLa cells is about 88%.

Advances in Na+,K+-ATPase studies: from protein to gene and back to protein

Complete primary structures of both subunits of Na+,K+-ATPase from various sources have been established by a combination of the methods for molecular cloning and protein chemistry. The gene family homologous to the alpha-subunit cDNA of animal Na+,K+-ATPases has been found in the human genome. Some genes of this family encode the known isoforms (alpha I and alpha II) of the Na+,K+-ATPase catalytic subunit. The proteins coded by other genes can be either new isoforms of the Na+,K+-ATPase catalytic subunit or other ion-transporting ATPases. Expression of the genes of this family proceeds in a tissue-specific manner and changes during the postnatal development and neoplastic transformation. The complete exon-intron structure of one of the genes of this family has been established. This gene codes for the form of the catalytic subunit, the existence of which has been unknown. Apparently, all the genes of the discovered family have a similar intron-exon structure. There is certain correlation between the gene structure and the proposed domain arrangement of the alpha-subunit. The results obtained have become the basis for the experiments which prove the existence of the earlier unknown alpha III isoform of the Na+,K+-ATPase catalytic subunit and have made possible the study of its function.

Structure of the alpha 1 subunit of horse Na,K-ATPase gene

Genomic DNA for Na,K-ATPase alpha 1 subunit was obtained from libraries of horse kidney genomic DNA in Charon 4A and in EMBL3 bacteriophages by screening with the full sized cDNA probe of the alpha 1 subunit of rat Na,K-ATPase as probe. The gene spans 30 kb and consists of 23 exons and 22 intervening sequences. Intron-exon boundaries were analyzed. The protein-coding nucleotide sequence encodes 1016 amino acids with an Mr of 112,264. The putative amino acid sequence of horse alpha 1 is 96-97% homologous to those of other mammalian species.

Family of human Na+,K+-ATPase genes. Structure of the putative regulatory region of the alpha+-gene

The primary structure of the putative regulatory region of a gene of the Na+,K+-ATPase multigene family in the human genome has been determined. This region includes the first exon with all of the untranslatable sequence of mRNA and a dozen nucleotides, coding for the first four amino acids of the hypothetic precursor of the alpha+-subunit. The entire region comprises over 1400 bp. The possible role of specific nucleotide blocks within this region in comparison with other genes is discussed.

Na+,K+-ATPase: tissue-specific expression of genes coding for alpha-subunit in diverse human tissues

The expression of genes coding for alpha and alpha III isoforms of Na+,K+-ATPase alpha-subunit has been studied in human kidney, brain, thyroid and liver cells. The expression was shown to be subjected to a tissue-specific control and also depended on the developmental stage. The tissue-specific expression of genes coding for different isoforms of the catalytic subunit of Na+,K+-ATPase perhaps may be attributed to various functions of proteins belonging to this family.

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

The primary structure of a gene of the Na+, K+-ATPase multigenic family in the human genome has been determined. The gene corresponds to a hypothetical alpha III-form of the enzyme catalytic subunit. The gene comprises over 25,000 bp, and its protein coding region includes 23 exons and 22 introns. Possible correlation between structural features of the protein and location of introns in the gene are discussed.

Chromosomal localization of human Na+, K+-ATPase alpha- and beta-subunit genes

Na+, K+-ATPase is a heterodimeric enzyme responsible for the active maintenance of sodium and potassium gradients across the plasma membrane. Recently, cDNAs for several tissue-specific isoforms of the larger catalytic alpha-subunit and the smaller beta-subunit have been cloned. We have hybridized rat brain and human kidney cDNA probes, as well as human genomic isoform-specific DNA fragments, to Southern filters containing panels of rodent X human somatic cell hybrid lines. The results obtained have allowed us to assign the loci for the ubiquitously expressed alpha-chain (ATP1A1) to human chromosome 1, region 1p21----cen, and for the alpha 2 isoform that predominates in neural and muscle tissues (ATP1A2) to chromosome 1, region cen----q32. A common PstI RFLP was detected with the ATP1A2 probe. The alpha 3 gene, which is expressed primarily in neural tissues (ATP1A3), was assigned to human chromosome 19. A fourth alpha gene of unknown function (alpha D) that was isolated by molecular cloning (ATP1AL1) was mapped to chromosome 13. Although evidence to date had suggested a single gene for the beta-subunit, we found hybridizing restriction fragments derived from two different human chromosomes. On the basis of knowledge of conserved linkage groups on human and murine chromosomes, we propose that the coding gene ATP 1B is located on the long arm of human chromosome 1 and that the sequence on human chromosome 4 (ATP 1BL1) is either a related gene or a pseudogene.

Family of Na+,K+-ATPase genes. Intra-individual tissue-specific restriction fragment length polymorphism

Intra-individual tissue-specific restriction fragment length polymorphism (RFLP) has been demonstrated in DNA isolated from different mammalian tissues using cDNAs of alpha- and beta-subunits of Na+,K+-ATPase as hybridization probes. We propose that the RFLPs could result from gene rearrangements in the gene loci for the alpha- and beta-subunits of Na+,K+-ATPase. The changes in restriction patterns have been shown to occur during embryonic development and tumor formation. In addition, the tissue specificity of the expression of different genes of the family of Na+,K+-ATPase genes and their low expression in tumor cells have been demonstrated.

The family of human Na+,K+-ATPase genes. No less than five genes and/or pseudogenes related to the alpha-subunit

Five different nucleotide sequences have been found in the human genome homologous to the gene of the alpha-subunit of Na+,K+-ATPase. A comparative analysis of the primary structure of these genes in the region 749-1328 (in coordinates of cDNA from the pig alpha-subunit) is presented.