Global citation inequality is on the rise.

Citations are important building blocks for status and success in science. We used a linked dataset of more than 4 million authors and 26 million scientific papers to quantify trends in cumulative citation inequality and concentration at the author level. Our analysis, which spans 15 y and 118 scientific disciplines, suggests that a small stratum of elite scientists accrues increasing citation shares and that citation inequality is on the rise across the natural sciences, medical sciences, and agricultural sciences. The rise in citation concentration has coincided with a general inclination toward more collaboration. While increasing collaboration and full-count publication rates go hand in hand for the top 1% most cited, ordinary scientists are engaging in more and larger collaborations over time, but publishing slightly less. Moreover, fractionalized publication rates are generally on the decline, but the top 1% most cited have seen larger increases in coauthored papers and smaller relative decreases in fractional-count publication rates than scientists in the lower percentiles of the citation distribution. Taken together, these trends have enabled the top 1% to extend its share of fractional- and full-count publications and citations. Further analysis shows that top-cited scientists increasingly reside in high-ranking universities in western Europe and Australasia, while the United States has seen a slight decline in elite concentration. Our findings align with recent evidence suggesting intensified international competition and widening author-level disparities in science.

A structural overview of the plasma membrane Na+,K+-ATPase and H+-ATPase ion pumps.

Plasma membrane ATPases are primary active transporters of cations that maintain steep concentration gradients. The ion gradients and membrane potentials derived from them form the basis for a range of essential cellular processes, in particular Na(+)-dependent and proton-dependent secondary transport systems that are responsible for uptake and extrusion of metabolites and other ions. The ion gradients are also both directly and indirectly used to control pH homeostasis and to regulate cell volume. The plasma membrane H(+)-ATPase maintains a proton gradient in plants and fungi and the Na(+),K(+)-ATPase maintains a Na(+) and K(+) gradient in animal cells. Structural information provides insight into the function of these two distinct but related P-type pumps.

The SERCA residue Glu340 mediates interdomain communication that guides Ca2+ transport.

The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a P-type ATPase that transports Ca2+ from the cytosol into the sarco(endo)plasmic reticulum (SR/ER) lumen, driven by ATP. This primary transport activity depends on tight coupling between movements of the transmembrane helices forming the two Ca2+-binding sites and the cytosolic headpiece mediating ATP hydrolysis. We have addressed the molecular basis for this intramolecular communication by analyzing the structure and functional properties of the SERCA mutant E340A. The mutated Glu340 residue is strictly conserved among the P-type ATPase family of membrane transporters and is located at a seemingly strategic position at the interface between the phosphorylation domain and the cytosolic ends of 5 of SERCA's 10 transmembrane helices. The mutant displays a marked slowing of the Ca2+-binding kinetics, and its crystal structure in the presence of Ca2+ and ATP analog reveals a rotated headpiece, altered connectivity between the cytosolic domains, and an altered hydrogen bonding pattern around residue 340. Supported by molecular dynamics simulations, we conclude that the E340A mutation causes a stabilization of the Ca2+ sites in a more occluded state, hence displaying slowed dynamics. This finding underpins a crucial role of Glu340 in interdomain communication between the headpiece and the Ca2+-binding transmembrane region.

Phosphatidylserine flipping by the P4-ATPase ATP8A2 is electrogenic.

Phospholipid flippases (P4-ATPases) utilize ATP to translocate specific phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of biological membranes, thus generating and maintaining transmembrane lipid asymmetry essential for a variety of cellular processes. P4-ATPases belong to the P-type ATPase protein family, which also encompasses the ion transporting P2-ATPases: Ca2+-ATPase, Na+,K+-ATPase, and H+,K+-ATPase. In comparison with the P2-ATPases, understanding of P4-ATPases is still very limited. The electrogenicity of P4-ATPases has not been explored, and it is not known whether lipid transfer between membrane bilayer leaflets can lead to displacement of charge across the membrane. A related question is whether P4-ATPases countertransport ions or other substrates in the opposite direction, similar to the P2-ATPases. Using an electrophysiological method based on solid supported membranes, we observed the generation of a transient electrical current by the mammalian P4-ATPase ATP8A2 in the presence of ATP and the negatively charged lipid substrate phosphatidylserine, whereas only a diminutive current was generated with the lipid substrate phosphatidylethanolamine, which carries no or little charge under the conditions of the measurement. The current transient seen with phosphatidylserine was abolished by the mutation E198Q, which blocks dephosphorylation. Likewise, mutation I364M, which causes the neurological disorder cerebellar ataxia, mental retardation, and disequilibrium (CAMRQ) syndrome, strongly interfered with the electrogenic lipid translocation. It is concluded that the electrogenicity is associated with a step in the ATPase reaction cycle directly involved in translocation of the lipid. These measurements also showed that no charged substrate is being countertransported, thereby distinguishing the P4-ATPase from P2-ATPases.

Identification and functional analyses of disease-associated P4-ATPase phospholipid flippase variants in red blood cells.

ATP-dependent phospholipid flippase activity crucial for generating lipid asymmetry was first detected in red blood cell (RBC) membranes, but the P4-ATPases responsible have not been directly determined. Using affinity-based MS, we show that ATP11C is the only abundant P4-ATPase phospholipid flippase in human RBCs, whereas ATP11C and ATP8A1 are the major P4-ATPases in mouse RBCs. We also found that ATP11A and ATP11B are present at low levels. Mutations in the gene encoding ATP11C are responsible for blood and liver disorders, but the disease mechanisms are not known. Using heterologous expression, we show that the T415N substitution in the phosphorylation motif of ATP11C, responsible for congenital hemolytic anemia, reduces ATP11C expression, increases retention in the endoplasmic reticulum, and decreases ATPase activity by 61% relative to WT ATP11C. The I355K substitution in the transmembrane domain associated with cholestasis and anemia in mice was expressed at WT levels and trafficked to the plasma membrane but was devoid of activity. We conclude that the T415N variant causes significant protein misfolding, resulting in low protein expression, cellular mislocalization, and reduced functional activity. In contrast, the I355K variant folds and traffics normally but lacks key contacts required for activity. We propose that the loss in ATP11C phospholipid flippase activity coupled with phospholipid scramblase activity results in the exposure of phosphatidylserine on the surface of RBCs, decreasing RBC survival and resulting in anemia.

Asparagine 905 of the mammalian phospholipid flippase ATP8A2 is essential for lipid substrate-induced activation of ATP8A2 dephosphorylation.

The P-type ATPase protein family includes, in addition to ion pumps such as Ca2+-ATPase and Na+,K+-ATPase, also phospholipid flippases that transfer phospholipids between membrane leaflets. P-type ATPase ion pumps translocate their substrates occluded between helices in the center of the transmembrane part of the protein. The large size of the lipid substrate has stimulated speculation that flippases use a different transport mechanism. Information on the functional importance of the most centrally located helices M5 and M6 in the transmembrane domain of flippases has, however, been sparse. Using mutagenesis, we examined the entire M5-M6 region of the mammalian flippase ATP8A2 to elucidate its possible function in the lipid transport mechanism. This mutational screen yielded an informative map assigning important roles in the interaction with the lipid substrate to only a few M5-M6 residues. The M6 asparagine Asn-905 stood out as being essential for the lipid substrate-induced dephosphorylation. The mutants N905A/D/E/H/L/Q/R all displayed very low activities and a dramatic insensitivity to the lipid substrate. Strikingly, Asn-905 aligns with key ion-binding residues of P-type ATPase ion pumps, and N905D was recently identified as one of the mutations causing the neurological disorder cerebellar ataxia, mental retardation, and disequilibrium (CAMRQ) syndrome. Moreover, the effects of substitutions to the adjacent residue Val-906 (i.e. V906A/E/F/L/Q/S) suggest that the lipid substrate approaches Val-906 during the translocation. These results favor a flippase mechanism with strong resemblance to the ion pumps, despite a location of the translocation pathway in the periphery of the transmembrane part of the flippase protein.

Alpha-synuclein aggregates activate calcium pump SERCA leading to calcium dysregulation.

Aggregation of α-synuclein is a hallmark of Parkinson's disease and dementia with Lewy bodies. We here investigate the relationship between cytosolic Ca2+ and α-synuclein aggregation. Analyses of cell lines and primary culture models of α-synuclein cytopathology reveal an early phase with reduced cytosolic Ca2+ levels followed by a later Ca2+ increase. Aggregated but not monomeric α-synuclein binds to and activates SERCA in vitro, and proximity ligation assays confirm this interaction in cells. The SERCA inhibitor cyclopiazonic acid (CPA) normalises both the initial reduction and the later increase in cytosolic Ca2+ CPA protects the cells against α-synuclein-aggregate stress and improves viability in cell models and in Caenorhabditis elegans in vivo Proximity ligation assays also reveal an increased interaction between α-synuclein aggregates and SERCA in human brains affected by dementia with Lewy bodies. We conclude that α-synuclein aggregates bind SERCA and stimulate its activity. Reducing SERCA activity is neuroprotective, indicating that SERCA and down-stream processes may be therapeutic targets for treating α-synucleinopathies.

A Darier disease mutation relieves kinetic constraints imposed by the tail of sarco(endo)plasmic reticulum Ca2+-ATPase 2b.

The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) 2b isoform possesses an extended C terminus (SERCA2b tail) forming an 11th transmembrane (TM) helix, which slows conformational changes of the Ca2+-pump reaction cycle. Here, we report that a Darier disease (DD) mutation of SERCA2b that changes a glutamate to a lysine in the cytoplasmic loop between TM8 and TM9 (E917K) relieves these kinetic constraints. We analyzed the effects of this mutation on the overall reaction and the individual partial reactions of the Ca2+ pump compared with the corresponding mutations of the SERCA2a and SERCA1a isoforms, lacking the SERCA2b tail. In addition to a reduced affinity for Ca2+, caused by the mutation in all three isoforms examined, we observed a unique enhancing effect on the turnover rates of ATPase activity and Ca2+ transport for the SERCA2b E917K mutation. This relief of kinetic constraints contrasted with inhibitory effects observed for the corresponding SERCA2a and SERCA1a (E918K) mutations. These observations indicated that the E917K/E918K mutations affect the rate-limiting conformational change in isoform-specific ways and that the SERCA2b mutation perturbs the interactions of TM11 with other SERCA2b regions. Mutational analysis of an arginine in TM7 that interacts with the glutamate in SERCA1a crystal structures suggested that in wildtype SERCA2b, the corresponding arginine (Arg-835) may be involved in mediating the conformational restriction by TM11. Moreover, the E917K mutation may disturb TM11 through the cytoplasmic loop between TM10 and TM11. In conclusion, our findings have identified structural elements of importance for the kinetic constraints imposed by TM11.

SERCA mutant E309Q binds two Ca(2+) ions but adopts a catalytically incompetent conformation.

The sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) couples ATP hydrolysis to transport of Ca(2+). This directed energy transfer requires cross-talk between the two Ca(2+) sites and the phosphorylation site over 50 Å distance. We have addressed the mechano-structural basis for this intramolecular signal by analysing the structure and the functional properties of SERCA mutant E309Q. Glu(309) contributes to Ca(2+) coordination at site II, and a consensus has been that E309Q only binds Ca(2+) at site I. The crystal structure of E309Q in the presence of Ca(2+) and an ATP analogue, however, reveals two occupied Ca(2+) sites of a non-catalytic Ca2E1 state. Ca(2+) is bound with micromolar affinity by both Ca(2+) sites in E309Q, but without cooperativity. The Ca(2+)-bound mutant does phosphorylate from ATP, but at a very low maximal rate. Phosphorylation depends on the correct positioning of the A-domain, requiring a shift of transmembrane segment M1 into an 'up and kinked position'. This transition is impaired in the E309Q mutant, most likely due to a lack of charge neutralization and altered hydrogen binding capacities at Ca(2+) site II.

Critical roles of isoleucine-364 and adjacent residues in a hydrophobic gate control of phospholipid transport by the mammalian P4-ATPase ATP8A2.

P4-ATPases (flippases) translocate specific phospholipids such as phosphatidylserine from the exoplasmic leaflet of the cell membrane to the cytosolic leaflet, upholding an essential membrane asymmetry. The mechanism of flipping this giant substrate has remained an enigma. We have investigated the importance of amino acid residues in transmembrane segment M4 of mammalian P4-ATPase ATP8A2 by mutagenesis. In the related ion pumps Na(+),K(+)-ATPase and Ca(2+)-ATPase, M4 moves during the enzyme cycle, carrying along the ion bound to a glutamate. In ATP8A2, the corresponding residue is an isoleucine, which recently was found mutated in patients with cerebellar ataxia, mental retardation, and dysequilibrium syndrome. Our analyses of the lipid substrate concentration dependence of the overall and partial reactions of the enzyme cycle in mutants indicate that, during the transport across the membrane, the phosphatidylserine head group passes near isoleucine-364 (I364) and that I364 is critical to the release of the transported lipid into the cytosolic leaflet. Another M4 residue, N359, is involved in recognition of the lipid substrate on the exoplasmic side. Our functional studies are supported by structural homology modeling and molecular dynamics simulations, suggesting that I364 and adjacent hydrophobic residues function as a hydrophobic gate that separates the entry and exit sites of the lipid and directs sequential formation and annihilation of water-filled cavities, thereby enabling transport of the hydrophilic phospholipid head group in a groove outlined by the transmembrane segments M1, M2, M4, and M6, with the hydrocarbon chains following passively, still in the membrane lipid phase.

Rescue of defective ATP8B1 trafficking by CFTR correctors as a therapeutic strategy for familial intrahepatic cholestasis.

BACKGROUND & AIMS: ATP8B1 deficiency is an autosomal recessive liver disease characterized by intrahepatic cholestasis. ATP8B1 mutation p.I661T, the most frequent mutation in European patients, results in protein misfolding and impaired targeting to the plasma membrane. Similarly, mutations in cystic fibrosis transmembrane conductance regulator (CFTR), associated with cystic fibrosis, impair protein folding and trafficking. The aim of this study was to investigate whether compounds that rescue CFTR F508del trafficking are capable of improving p.I661T-ATP8B1 plasma membrane expression. METHODS: The effect of CFTR corrector compounds on plasma membrane expression of p.I661T-ATP8B1 was evaluated by cell surface biotinylation and immunofluorescence. ATPase activity was evaluated of a purified analogue protein carrying a mutation at the matching position (p.L622T-ATP8A2). RESULTS: The clinically used compounds, 4-phenylbutyric acid (4-PBA), suberoylanilide hydroxamic acid (SAHA) and N-butyldeoxynojirimycin (NB-DNJ) improved p.I661T-ATP8B1 plasma membrane targeting. Compounds C4, C5, C13 and C17 also significantly increased plasma membrane expression of p.I661T-ATP8B1. SAHA and compound C17 upregulated ATP8B1 transcription. p.I661T-ATP8B1 was partly targeted to the canalicular membrane in polarized cells, which became more evident upon treatment with SAHA and/or C4. p.L622T-ATP8A2 showed phospholipid-induced ATPase activity, suggesting that mutations at a matching position in ATP8B1 do not block functionality. Combination therapy of SAHA and compound C4 resulted in an additional improvement of ATP8B1 cell surface abundance. CONCLUSIONS: This study shows that several CFTR correctors can improve trafficking of p.I661T-ATP8B1 to the plasma membrane in vitro. Hence, these compounds may be suitable to be part of a future therapy for ATP8B1 deficiency and other genetic disorders associated with protein misfolding. LAY SUMMARY: Compounds that improve the cellular machinery dealing with protein homeostasis (proteostasis) and allow for proper folding of proteins with (mild) missense mutations are called proteostasis regulators (Balch, Science 2008). Such compounds are potentially of high therapeutic value for many (liver) diseases. In this manuscript, we investigated whether compounds identified in screens as CFTR folding correctors are actually proteostasis regulators and thus have a broader application in other protein folding diseases. Using these compounds, we could indeed show improved trafficking to the (apical) plasma membrane of a mutated ATP8B1 protein, carrying the p.I661T missense mutation. This is the most frequently identified mutation in this rare cholestatic disorder. Importantly, ATP8B1 shows no similarity to CFTR. These data are important in providing support for the concept that rare, genetic liver diseases can potentially be treated using a generalized strategy.

Critical roles of interdomain interactions for modulatory ATP binding to sarcoplasmic reticulum Ca2+-ATPase.

ATP has dual roles in the reaction cycle of sarcoplasmic reticulum Ca(2+)-ATPase. Upon binding to the Ca2E1 state, ATP phosphorylates the enzyme, and by binding to other conformational states in a non-phosphorylating modulatory mode ATP stimulates the dephosphorylation and other partial reaction steps of the cycle, thereby ensuring a high rate of Ca(2+) transport under physiological conditions. The present study elucidates the mechanism underlying the modulatory effect on dephosphorylation. In the intermediate states of dephosphorylation the A-domain residues Ser(186) and Asp(203) interact with Glu(439) (N-domain) and Arg(678) (P-domain), respectively. Single mutations to these residues abolish the stimulation of dephosphorylation by ATP. The double mutation swapping Asp(203) and Arg(678) rescues ATP stimulation, whereas this is not the case for the double mutation swapping Ser(186) and Glu(439). By taking advantage of the ability of wild type and mutant Ca(2+)-ATPases to form stable complexes with aluminum fluoride (E2·AlF) and beryllium fluoride (E2·BeF) as analogs of the E2·P phosphoryl transition state and E2P ground state, respectively, of the dephosphorylation reaction, the mutational effects on ATP binding to these intermediates are demonstrated. In the wild type Ca(2+)-ATPase, the ATP affinity of the E2·P phosphoryl transition state is higher than that of the E2P ground state, thus explaining the stimulation of dephosphorylation by nucleotide-induced transition state stabilization. We find that the Asp(203)-Arg(678) and Ser(186)-Glu(439) interdomain bonds are critical, because they tighten the interaction with ATP in the E2·P phosphoryl transition state. Moreover, ATP binding and the Ser(186)-Glu(439) bond are mutually exclusive in the E2P ground state.

Critical role of a transmembrane lysine in aminophospholipid transport by mammalian photoreceptor P4-ATPase ATP8A2.

ATP8A2 is a P(4)-ATPase ("flippase") located in membranes of retinal photoreceptors, brain cells, and testis, where it mediates transport of aminophospholipids toward the cytoplasmic leaflet. It has long been an enigma whether the mechanism of P(4)-ATPases resembles that of the well-characterized cation-transporting P-type ATPases, and it is unknown whether the flippases interact directly with the lipid and with counterions. Our results demonstrate that ATP8A2 forms a phosphoenzyme intermediate at the conserved aspartate (Asp(416)) in the P-type ATPase signature sequence and exists in E(1)P and E(2)P forms similar to the archetypical P-type ATPases. Using the properties of the phosphoenzyme, the partial reaction steps of the transport cycle were examined, and the roles of conserved residues Asp(196), Glu(198), Lys(873), and Asn(874) in the transport mechanism were elucidated. The former two residues in the A-domain T/D-G-E-S/T motif are involved in catalysis of E(2)P dephosphorylation, the glutamate being essential. Transported aminophospholipids activate the dephosphorylation similar to K(+) activation of dephosphorylation in Na(+),K(+)-ATPase. Lys(873) mutants (particularly K873A and K873E) display a markedly reduced sensitivity to aminophospholipids. Hence, Lys(873), located in transmembrane segment M5 at a "hot spot" for cation binding in Ca(2+)-ATPase and Na(+),K(+)-ATPase, appears to participate directly in aminophospholipid binding or to mediate a crucial interaction within the ATP8A2-CDC50 complex. By contrast, Lys(865) is unimportant for aminophospholipid sensitivity. Binding of Na(+), H(+), K(+), Cl(-), or Ca(2+) to the E(1) form as a counterion is not required for activation of phosphorylation from ATP. Therefore, phospholipids could be the only substrate transported by ATP8A2.

Funding priorities and health outcomes in Danish medical research.

External research funding is an essential component of the infrastructure of modern, academic research. Priorities in funding decisions drive what knowledge is generated, and how scientists' careers are shaped. For health research, it can ultimately have implications for health outcomes. The aim of this paper is to illustrate how funding information can be used to track priorities in health research, linking them to disease burdens and research outputs. Furthermore, funding concentrations are analysed from both researcher and disease perspectives, to estimate the influence of personal Matthew-effects on the distribution of health research funding. Denmark is used as the case, including funding information from all major public and private research foundations in the period 2004-2016. Grant information is linked to research outputs and disability-adjusted life-years (DALY rates), for 34,160 publications linked to 2630 grants, receiving DKK 4.8 billion in funding. Data show poor correlation between funding priorities, research activity and disease burdens, with several diseases receiving disproportionate amounts of funding. A research opportunity index is calculated to identify diseases with the highest potential for future investments from a burden-centred point of view. Funding is highly concentrated, both on people and on specific diseases. High funding concentrations on researchers can be a driving factor behind the observed funding-to-burden imbalances, and may risk knowledge stagnation through monopolisation of the market place of ideas. Results indicate that funders of clinical and translational research, as well as some types of biomedical research, need to supplement traditional considerations of scientific excellence with measures of societal challenges and relevance.

Functional and in silico analysis of ATP8A2 and other P4-ATPase variants associated with human genetic diseases.

P4-ATPases flip lipids from the exoplasmic to cytoplasmic leaflet of cell membranes, a property crucial for many biological processes. Mutations in P4-ATPases are associated with severe inherited and complex human disorders. We determined the expression, localization and ATPase activity of four variants of ATP8A2, the P4-ATPase associated with the neurodevelopmental disorder known as cerebellar ataxia, impaired intellectual development and disequilibrium syndrome 4 (CAMRQ4). Two variants, G447R and A772P, harboring mutations in catalytic domains, expressed at low levels and mislocalized in cells. In contrast, the E459Q variant in a flexible loop displayed wild-type expression levels, Golgi-endosome localization and ATPase activity. The R1147W variant expressed at 50% of wild-type levels but showed normal localization and activity. These results indicate that the G447R and A772P mutations cause CAMRQ4 through protein misfolding. The E459Q mutation is unlikely to be causative, whereas the R1147W may display a milder disease phenotype. Using various programs that predict protein stability, we show that there is a good correlation between the experimental expression of the variants and in silico stability assessments, suggesting that such analysis is useful in identifying protein misfolding disease-associated variants.

Na+,K+-ATPase with Disrupted Na+ Binding Sites I and III Binds Na+ with Increased Affinity at Site II and Undergoes Na+-Activated Phosphorylation with ATP.

Na+,K+-ATPase actively extrudes three cytoplasmic Na+ ions in exchange for two extracellular K+ ions for each ATP hydrolyzed. The atomic structure with bound Na+ identifies three Na+ sites, named I, II, and III. It has been proposed that site III is the first to be occupied and site II last, when Na+ binds from the cytoplasmic side. It is usually assumed that the occupation of all three Na+ sites is obligatory for the activation of phosphoryl transfer from ATP. To obtain more insight into the individual roles of the ion-binding sites, we have analyzed a series of seven mutants with substitution of the critical ion-binding residue Ser777, which is a shared ligand between Na+ sites I and III. Surprisingly, mutants with large and bulky substituents expected to prevent or profoundly disturb Na+ access to sites I and III retain the ability to form a phosphoenzyme from ATP, even with increased apparent Na+ affinity. This indicates that Na+ binding solely at site II is sufficient to promote phosphorylation. These mutations appear to lock the membrane sector into an E1-like configuration, allowing Na+ but not K+ to bind at site II, while the cytoplasmic sector undergoes conformational changes uncoupled from the membrane sector.

Is something rotten in the state of Denmark? Cross-national evidence for widespread involvement but not systematic use of questionable research practices across all fields of research.

Questionable research practices (QRP) are believed to be widespread, but empirical assessments are generally restricted to a few types of practices. Furthermore, conceptual confusion is rife with use and prevalence of QRPs often being confused as the same quantity. We present the hitherto most comprehensive study examining QRPs across scholarly fields and knowledge production modes. We survey perception, use, prevalence and predictors of QRPs among 3,402 researchers in Denmark and 1,307 in the UK, USA, Croatia and Austria. Results reveal remarkably similar response patterns among Danish and international respondents (τ = 0.85). Self-reported use indicates whether respondents have used a QRP in recent publications. 9 out of 10 respondents admitted using at least one QRP. Median use is three out of nine QRP items. Self-reported prevalence reflects the frequency of use. On average, prevalence rates were roughly three times lower compared to self-reported use. Findings indicated that the perceived social acceptability of QRPs influenced self-report patterns. Results suggest that most researchers use different types of QRPs within a restricted time period. The prevalence estimates, however, do not suggest outright systematic use of specific QRPs. Perceived pressure was the strongest systemic predictor for prevalence. Conversely, more local attention to research cultures and academic age was negatively related to prevalence. Finally, the personality traits conscientiousness and, to a lesser degree, agreeableness were also inversely associated with self-reported prevalence. Findings suggest that explanations for engagement with QRPs are not only attributable to systemic factors, as hitherto suggested, but a complicated mixture of experience, systemic and individual factors, and motivated reasoning.

Distinct roles of the C-terminal 11th transmembrane helix and luminal extension in the partial reactions determining the high Ca2+ affinity of sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2b (SERCA2b).

The molecular mechanism underlying the characteristic high apparent Ca(2+) affinity of SERCA2b relative to SERCA1a and SERCA2a isoforms was studied. The C-terminal tail of SERCA2b consists of an 11th transmembrane helix (TM11) with an associated 11-amino acid luminal extension (LE). The effects of each of these parts and their interactions with the SERCA environment were examined by transient kinetic analysis of the partial reaction steps in the Ca(2+) transport cycle in mutant and chimeric Ca(2+)-ATPase constructs. Manipulations to the LE of SERCA2b markedly increased the rate of Ca(2+) dissociation from Ca(2)E1. Addition of the SERCA2b tail to SERCA1a slowed Ca(2+) dissociation, but only when the luminal L7/8 loop of SERCA1 was simultaneously replaced with that of SERCA2, thus suggesting that the LE interacts with L7/8 in Ca(2)E1. The interaction of LE with L7/8 is also important for the low rate of the Ca(2)E1P → E2P conformational transition. These findings can be rationalized in terms of stabilization of the Ca(2)E1 and Ca(2)E1P forms by docking of the LE near L7/8. By contrast, low rates of E2P dephosphorylation and E2 → E1 transition in SERCA2b depend critically on TM11, particularly in a SERCA2 environment, but do not at all depend on the LE or L7/8. This indicates that interaction of TM11 with SERCA2-specific sequence element(s) elsewhere in the structure is critical in the Ca(2+)-free E2/E2P states. Collectively these properties ensure a higher Ca(2+) affinity of SERCA2b relative to other SERCA isoforms, not only on the cytosolic side, but also on the luminal side.

Crystal structure of the sodium-potassium pump.

The Na+,K+-ATPase generates electrochemical gradients for sodium and potassium that are vital to animal cells, exchanging three sodium ions for two potassium ions across the plasma membrane during each cycle of ATP hydrolysis. Here we present the X-ray crystal structure at 3.5 A resolution of the pig renal Na+,K+-ATPase with two rubidium ions bound (as potassium congeners) in an occluded state in the transmembrane part of the alpha-subunit. Several of the residues forming the cavity for rubidium/potassium occlusion in the Na+,K+-ATPase are homologous to those binding calcium in the Ca2+-ATPase of sarco(endo)plasmic reticulum. The beta- and gamma-subunits specific to the Na+,K+-ATPase are associated with transmembrane helices alphaM7/alphaM10 and alphaM9, respectively. The gamma-subunit corresponds to a fragment of the V-type ATPase c subunit. The carboxy terminus of the alpha-subunit is contained within a pocket between transmembrane helices and seems to be a novel regulatory element controlling sodium affinity, possibly influenced by the membrane potential.