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P-type ATPases: Many more enigmas left to solve.

ABSTRACT: P-type ATPases constitute a large ancient super-family of primary active pumps that have diverse substrate specificities ranging from H⁺ to phospholipids. The significance of these enzymes in biology cannot be overstated. They are structurally related, and their catalytic cycles alternate between high- and low-affinity conformations that are induced by phosphorylation and dephosphorylation of a conserved aspartate residue. In the year 1988, all P-type sequences available by then were analyzed and five major families, P1 to P5, were identified. Since then, a large body of knowledge has accumulated concerning the structure, function, and physiological roles of members of these families, but only one additional family, P6 ATPases, has been identified. However, much is still left to be learned. For each family a few remaining enigmas are presented, with the intention that they will stimulate interest in continued research in the field. The review is by no way comprehensive and merely presents personal views with a focus on evolution.

SUBMITTER: Palmgren M

PROVIDER: S-EPMC10654040 | biostudies-literature | 2023 Oct

REPOSITORIES: biostudies-literature

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P-type ATPases: Many more enigmas left to solve.

Palmgren Michael M

The Journal of biological chemistry 20231012 11

P-type ATPases constitute a large ancient super-family of primary active pumps that have diverse substrate specificities ranging from H<sup>+</sup> to phospholipids. The significance of these enzymes in biology cannot be overstated. They are structurally related, and their catalytic cycles alternate between high- and low-affinity conformations that are induced by phosphorylation and dephosphorylation of a conserved aspartate residue. In the year 1988, all P-type sequences available by then were ...[more]

PMID: 37838176

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Project description:P4-ATPases comprise a family of P-type ATPases that actively transport or flip phospholipids across cell membranes. This generates and maintains membrane lipid asymmetry, a property essential for a wide variety of cellular processes such as vesicle budding and trafficking, cell signaling, blood coagulation, apoptosis, bile and cholesterol homeostasis, and neuronal cell survival. Some P4-ATPases transport phosphatidylserine and phosphatidylethanolamine across the plasma membrane or intracellular membranes whereas other P4-ATPases are specific for phosphatidylcholine. The importance of P4-ATPases is highlighted by the finding that genetic defects in two P4-ATPases ATP8A2 and ATP8B1 are associated with severe human disorders. Recent studies have provided insight into how P4-ATPases translocate phospholipids across membranes. P4-ATPases form a phosphorylated intermediate at the aspartate of the P-type ATPase signature sequence, and dephosphorylation is activated by the lipid substrate being flipped from the exoplasmic to the cytoplasmic leaflet similar to the activation of dephosphorylation of Na(+)/K(+)-ATPase by exoplasmic K(+). How the phospholipid is translocated can be understood in terms of a peripheral hydrophobic gate pathway between transmembrane helices M1, M3, M4, and M6. This pathway, which partially overlaps with the suggested pathway for migration of Ca(2+) in the opposite direction in the Ca(2+)-ATPase, is wider than the latter, thereby accommodating the phospholipid head group. The head group is propelled along against its concentration gradient with the hydrocarbon chains projecting out into the lipid phase by movement of an isoleucine located at the position corresponding to an ion binding glutamate in the Ca(2+)- and Na(+)/K(+)-ATPases. Hence, the P4-ATPase mechanism is quite similar to the mechanism of these ion pumps, where the glutamate translocates the ions by moving like a pump rod. The accessory subunit CDC50 may be located in close association with the exoplasmic entrance of the suggested pathway, and possibly promotes the binding of the lipid substrate. This review focuses on properties of mammalian and yeast P4-ATPases for which most mechanistic insight is available. However, the structure, function and enigmas associated with mammalian and yeast P4-ATPases most likely extend to P4-ATPases of plants and other organisms.

Project description:BackgroundThe growth and acceptance of osteopathic physicians as conventional medical practitioners in the United States has also raised questions about the distinctive aspects of osteopathic medicine. Although the use of osteopathic manipulative treatment (OMT) and a focus on primary care are most often cited as rationales for the uniqueness of osteopathic medicine, an osteopathic professional identity remains enigmatic.DiscussionThe fledgling basic osteopathic research efforts of the early and mid-twentieth century have not been sustained and expanded over time. Thus, there is presently a scarcity of basic mechanistic and translational research that can be considered to be uniquely osteopathic. To be sure, there have been advances in osteopathic clinical trials, particularly those involving OMT for low back pain. Meta-analysis of these low back pain trials has provided evidence that: (1) OMT affords greater pain reduction than active or placebo control treatments; (2) the effects of OMT are comparable regardless of whether treatment is provided by fully-licensed osteopathic physicians in the United States or by osteopaths in the United Kingdom; and (3) the effects of OMT increase over time. However, much more clinical research remains to be done. The planning and implementation of a large longitudinal study of the natural history and epidemiology of somatic dysfunction, including an OMT component, represents a much-needed step forward. Osteopathic medicine's use of OMT and its focus on primary care are not mutually exclusive aspects of its uniqueness. The intersection of these fundamental aspects of osteopathic medicine suggests that the profession may successfully adopt a generic strategy of "focused differentiation" to attain a competitive advantage in the health care arena. While there are both requisite demands and risks for the osteopathic profession in adopting such a strategy, these are reasonable in relation to the potential rewards to be attained. To help promote an osteopathic identity, "omtology" and its derivative terms are recommended in referring to the study of OMT.ConclusionThe osteopathic profession should adopt a coherent strategy for developing and promoting its identity. Failure to do so will likely ensure that osteopathic medicine remains "stuck in the middle."

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P-type ATPases: Many more enigmas left to solve.

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P-type ATPases: Many more enigmas left to solve.

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