CELL STRUCTURE AND FUNCTION 23: 315-323 (1998) MINI REVIEW © 1998 by Japan Society for Cell Biology Structures of P-type Transporting ATPases and ChromosomalLocations of Their Genes Masatomo Maeda1 *, Kunihiko Hamano1, Yuko Hirano1, Mikio Suzuki2, Ei-ichi Takahashi2, Tomoyuki Terada1, Masamitsu Futai3, and Ryuichiro Sato1 1Laboratory of Biochemistry and Molecular Biology, Graduate School of Pharmaceutical Sciences, Osaka Uni- versity, Suita, Osaka 565-0871, Japan, 2Gene Institute, Otsuka Pharmaceutical Company, Tokushima 771- 0130, Japan, and departmen t of Biological Sciences, The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan Keywords: channel/flippase/gene/ion transport/Mat-8/membrane recycling/P-type ATPase/sorting/transporting ATPase ABSTRACT. P-type ATPases (EiE2-ATPases) are primary active transporters which form phospho-interme- diates during their catalytic cycle. They are classified into PI to P4 based on the primary structure and poten- tial transmembrane segments. Although the classic P-type ATPasesare cation transporters, two newmembers have recently been found; one is a flippase catalyzing the flip-flop movement of aminophospholipids, but the substrate and function of the other one remain unknown.It would be interesting to determine whether the ca- tions and aminophospholipids are transported by similar or different mechanisms. P-type ATPases are be- lieved to have been derived from a commonancestor, and their genes are found to be distributed in various chromosomal loci. However, gene duplication events can be traced from the tandem arrangement of genes and their linkage map. Na+/K+- and H+/K+-ATPaseshave not only closely related a subunits but also similar fi subunits. Renal Na+/K+-ATPasehas an additional subunit y. Similar small polypeptides (phospholemman, Mat-8 and CHIF), which induce Cl~ and K+ currents, have been found. The idea of their functional and struc- tural coupling with P-type ATPases, especially with H+/K+-ATPase, is intriguing. Each P-type ATPase must have specific domains or sequences for its intracellular trafficking (sorting, retention and recycling). Identifica- tion of such regions and studies on the molecules playing role in their recognition mayfacilitate the unveiling of various cellular processes regulated by P-type ATPases. Prologue disorders (3). In this review, we focus on the P-type It is now widely accepted that the hydrolysis of ATP is ATPases, which are believed to be derived from a com- coupled to the transport of varieties of inorganic and monancestral gene (4). Well-known P-type ATPase organic ions across the various membranessurround- members such as Na+/K+-ATPase and Ca2+-ATPase ing cell and cytoplasmic organelle compartments. The play critical roles in regulating the intracellular ionic transporting ATPases (or pumpATPases) play essen- balance and driving physiological or biological proc- tial roles in this process. These ATPases are classified esses (1). into four group: P-type, F-type and V-type ATPases P-type ATPases have the unique property of the for- (1), and ABC-transporters (2). Information on the mation of a high-energy phosphate-bond with the car- primary structures of these ATPases and the chromo- boxyl moiety of a conserved aspartic acid residue. The somal locations of their genes is accumulating with the term of "P-type" is derived from this phospho-inter- progress of the genome projects and the identification mediate, whose bond energy is utilized to drive cation of the genes responsible for various human genetic movementthrough the membrane domain of the ATPase (1). P-type ATPase is a primary active trans- * To whomcorrespondence should be addressed. Tel: +81-6-6879-8185, Fax: +81-6-6875-8189 porter previously called EiE2-ATPase, since two con- Abbreviations used: FISH, fluorescence in situ hybridization; icformationalstudies (4).statesHowever,(Ei and novelE2) weremembersindicatedwhoseby kinet-sub- PCR, polymerase chain reaction; PMCA,plasma membrane Ca2+- ATPase; RACE, rapid amplification of CDNAends; SCAMP, secre- strates are aminophospholipids instead of cations have tory carrier membrane protein; SERCA,sarco/endoplasmic reticu- been found (5, 6). Wewill discuss the structural fea- lum Ca2+-ATPase; SNAP25, synaptosome-associated protein; V- tures of P-type ATPases, which are classified into three AMP,vesicle-associated membraneprotein. (7) or four (5) groups, the chromosomal locations of 315 M. Maeda et al. their genes, and then small single transmembrane poly- peptides. Pi -ATPase Structural features of P-type ATPases Each memberof the P-type ATPase family transports specific cations coupled with ATP hydrolysis and the formation of a high-energy phospho-intermediate through the DKTGsequence. Although the molecular weights of P-type ATPases are diverse (70-200 k), they have conserved motifs, such as [TGE(S/A)] in the con- formationally flexible loop, [DKTG(S/T)] in the phos- phorylation domain, (TGDN) in the ATP-binding do- main, and (MXGDGXNDXP)in the junction between the ATP-binding domain and the transmembrane seg- ment (7). Recently, P-type ATPases were classified into PI to P3 (Fig. 1) based on the type of transported ca- P2-ATPase tions and the putative transmembrane domains (7). The PI-ATPases involved in the transport of heavy metals (Cd2+, Cu2+ and Hg2+) have only two trans- membrane segments following the ATP-binding re- gion, whereas P2-ATPases have six (M5-M10). P2- Im.Mm^Mm^IJm. ms||m«|[mT|[mI][mT||mI| ATPases have four transmembrane segments (M1-M4) preceding the ATP-binding region. However, two hy- drophobic regions, which are potentially transmem- brane, are further inserted prior to the TGE(S/A) ^^^^á" NH2 sequence in PI-ATPases. PI-ATPases are also unique in that they have metal binding motifs (one to six of GMXCXXCor MXXMDHSXMsequences) in their amino-terminal regions, and have a transmembrane CP(C/H) sequence and a HP(L/V) sequence, each of P3-ATPase which precedes and follows a phosphorylation site (5, 8-12). It would be interesting to know how these motifs and sequences participate in metal transport. Although PI-ATPases generally transport heavy met- als from the cytoplasm to the outside, there is a bacte- rial enzymewhich catalyses the uptake of Cu2+from outside (9). PI-ATPases are also named CPx-type ATPases (10). P2-ATPases (non-heavy-metal-transporting P-type Fig. 1. Model of the transmembrane orientation of P-type ATPases. ATPases) have four additional transmembrane seg- The transmembrane orientation of PI, P2 and P3-ATPases is shown ments (M7-M10) compared with PI-ATPases. P2- (modified from ref 7). M1-M10indicate transmembrane segments. ATPases are classified into two subgroups. The Na+/ Unique transmembrane segments for each group are indicated by K+- and H+/K+-ATPasesubgroups have a catalytic a closed boxes. However, the authors of Ref. 10 reported that the 1st subunit and a glycosylated /3 subunit. They exchange and 2nd transmembrane segments of Pl-ATPase are unique. Thus, intracellular Na+ or H+with extracellular K+. Four the roles of these unique segments should be determined carefully in and three distinct Na+/K+- and H+/K+-ATPase a future studies. The positions of conserved amino acid sequences among P-type ATPases are schematically shown by small closed subunits, respectively, have been reported in mammals boxes with lower case letters [a, TGE(S/A); b, DKTG(S/T); c, TGDN; (Table I and the following). From recent studies, it was d, MXGDGXNDXP].Characteristic sequences of Pl-ATPase are established that H+/K+-ATPase a isoforms are ex- shown by open boxes [I, CP(C/H); II, HP(L/V)]. The ovals are met- pressed tissue-specifically in the stomach (al) (13), al binding motifs located in the amino-terminal region of Pl-ATPase. colon and kidney (al) (14, 15), and skin, kidney and P4-ATPasehas four or six transmembranesegments downstreamof the phosphorylation site (small closed box "b"), and the extracellular brain, but not in the colon (ATPlALl=a4) (15, 16). segment between Ml and M2is extremely iong (100-200 amino acid The mRNAs for two splicing isoforms of H+/K+- residues) (5). ATPase al increase coordinately in the kidney in re- sponse to chronic K+deprivation (14, 15). al is assem- 316 Stractures and Genes for P-type ATPase Table I. Chromosomal locations of P-type ATPase genes. A T P a se S u b u n it G en e H u m a n M o u se C o m m en ts R ef. N a + /K + a ¥ (a A ) A T P I A l l p l l- 1 3 3 u b iq u ito u s (26)-(3 6) al ( a B) A T P I A 2 I ce n- q32 1 n eu ra l , mu sc le a l A T P I A 3 1 9 q 13 .2 7 n eu ra l a D A T P I A L l 13 q 12 - 1 4 b ra in , k id n e y , sk in H + / K + -A T P a se (ｫ 4 ) a C A T P I A L 2 i Qcn. te stis 0 1 A T P IB I Iq 1 (2 7 ), (2 9) , B 2 A T P IB 2 l l (3 0 ), (3 6) J83 A T P IB 3 7 0 1 * A T P I B L l 4 p seu d o g en e H + / K + a (a l) A T P 4 A 1 9 q 13 .l l 7 (3 4 ), (3 7) p A T P 4 B 13 q 34 8 C u 2+ A T P 7 A X q 13 .3 X M en k e s d ise a se (3) , (37 W 4 0 ) A T P 7 B 1 3 q 14 .3 8 W il so n' s di se as e Ca2 + A T P 2 A 1 16 p 1 2 .1- 1 2 .2 7 B r od y d is e as e (4 1 W4 4) (sa rc o / e n d o -p la sm ic (S E R C A l) fa st-tw itc h [a d u lt (la ), retic u lu m ) n eo n a ta l (lb )] A T P 2 A 2 1 2 q 2 3 - 2 4 .