Membrane-bound ATPases

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Membrane-bound ATPases
Transporter classification
TCDB 3.A.
designation PP bond hydrolysis-powered transporter
Enzyme classification
EC, category 3.6.3.- ,  hydrolase
Substrate Adenosine diphosphate + phosphate or ATP
Products ATP or adenosine diphosphate + phosphate

Membrane bound ATPases are special ATPases , the structure or the degradation of ATP coupled with the transport of particles ( ions , small molecules, proteins ) from one side of the cell membrane , or organelle - membrane catalyze to another. They therefore play an important role in energy metabolism and signal transduction . These were discovered by the Danish physician Jens Christian Skou , who received the 1997 Nobel Prize in Chemistry .

According to the TCDB classification, the membrane-bound ATPases are PP-bond hydrolysis-driven transporters (TCDB 3.A ), which also include transporters that transfer their energy to pyrophosphates and other nucleotides than ATP, or from there Respectively. Because of their structure, they are molecular machines .

function

Hydrolysis of ATP

When membrane-bound ATPases consume energy, these are also known as ATP-dependent pumps. Such ATP-dependent pumps draw their energy from the splitting of the universal energy carrier ATP into ADP and phosphate .

Energy for the transport is necessary because such ATP-dependent pumps usually work against a gradient ( concentration gradient , electrochemical gradient, etc.). If the work were carried out along such a gradient, the particles would by themselves - possible causes could be a. be the Brownian molecular motion or electrochemical attractive forces - pass through the membrane. Lipophilic particles would simply be able to penetrate the membrane; hydrophilic particles would have to pass through the membrane through carrier or tunnel proteins.

The binding of the molecule to be transported to such pumps takes place according to the key-lock principle. ATP-dependent pumps, like enzymes or carrier proteins, are substrate-specific. A special chemical and spatial structure is therefore necessary. So only special molecules can dock.

The transport takes place as follows:

  1. Binding of the molecule to be transported to the substrate binding site in the protein
  2. Energy release through ATP splitting
  3. Change in the spatial structure of the protein (change in conformation) so that the molecule to be transported can be released on the other side of the membrane
  4. Return to the original state

Synthesis of ATP

The cellular ATPases . ATPases of the “P”, “V” and “F o F 1 ” types (F type) are shown in yellow and the mediated ion transport processes are indicated. "P-type" ATPases are characterized by a phosphorylated intermediate, which is indicated by a red symbol "~ P". The three basic types are shown along with their inhibition patterns at the bottom. SR, sarcoplasmic reticulum ; ER, endoplasmic reticulum ; AA, amino acid (derivative).

Energy is required to build ATP from ADP and phosphate. This energy comes from a proton gradient . If the protons diffuse through the channel according to their concentration gradient , the energy released can be used to produce ATP.

Types

A distinction is made between several types of membrane-bound ATPases such as ABC transporters , F and P types occur in both prokaryotes and eukaryotes , the V type is only found in eukaryotes. Other families exist, several of them exclusively in plants or bacteria. The direction in which an ATP synthase acts can also be reversed according to the chemical-osmotic equilibrium - the internal motor activity of the enzyme does not change anything (see DC machine : depending on the direction of the power flow: dynamo versus electric motor).

F-type ATPases (type 1)

(TCDB 3.A.2.1 ) These ATPases use a proton gradient for the synthesis of ATP from ADP. They are therefore called ATP synthases and can be found in the chloroplasts and mitochondria of eukaryotes as well as in prokaryotes (see chemiosmotic coupling ).

In the mitochondria, such an ATPase (F o F 1 -ATP synthase) consists of a membrane-bound Fo part (Note: This is not the F- "null" subunit, as is often wrongly pronounced, but the F- "o" - subunit. The "o" is derived from the oligomycin inhibitability of this subunit!), Which in Escherichia coli consists of three subunits, in eukaryotes of 10 subunits, which form the channel. The part F1 protruding into the matrix catalyzes the synthesis of ATP. 3 protons are transported for the synthesis of an ATP molecule. The V-type ATPases (V o V 1 -ATPases) and archaeal A-type ATPases (A o A 1 -ATPases) have a similar structure .

P-type ATPases (type 2)

(TCDB 3.A.3 ) These ATPases (sometimes also called E1-E2-ATPases) build up an ion gradient with hydrolysis of ATP. They differ significantly from the F-, A- and V-type ATPases in their structure from subunits; there are apparently no rotating elements. They are found in both prokaryotes and eukaryotes and consist of two subunits of approximately 100  kDa . In vitro , the conditions can be changed so that the Ca 2+ -ATPases can also synthesize ATP. The P-type ATPases are inhibited by orthovanadates ([VO 4 ] 3− ).

Uniport

(TCDB 3.A.3.2 ) Ca 2+ -ATPases in the cell membrane ensure that the Ca 2+ concentration in the cytosol remains low by pumping calcium ions from the cytosol into the extracellular space. This low concentration is necessary because, on the basis of signals, ion channels in the cell membrane or in the membrane of the endoplasmic (ER) and sarcoplasmic reticulum (SR) in nerve and muscle cells are opened, so that calcium ions pass passively and various processes in the Cell can initiate. The ATPases pump these calcium ions back again.

In Physcomitrella patens, a membrane-based Ca 2+ -ATPase pumps cytosolic Ca 2+ ions back into small vacuoles and is thus involved in the signal transduction of abiotic stress signals ( drought , salinization ) in addition to the phytohormone ABA . Knockout mosses for this gene are therefore more susceptible to abiotic stress.

In Escherichia coli, a K + -ATPase pumps potassium ions into the interior of the cell.

Antiport

(TCDB 3.A.3.1 ) The Na + -K + -exchanging ATPase ( sodium-potassium pump ) serves to maintain the ion concentrations of nerve cells. Three sodium ions are pumped outwards and two potassium ions are pumped inwards. It compensates for the leakage currents. Contrary to some ideas, it is not responsible for the repolarization during an action potential, the concentrations change only insignificantly during an action potential.

The H + -K + -exchanging ATPase ( proton-potassium pump ) in the membrane of the parietal cells of the stomach transports protons out of the cell and thus contributes to lowering the pH of the stomach acid . It acts directly as a proton pump .

V-type ATPases (type 3)

(TCDB 3.A.2.2 ) These ATPases (V o V 1 -ATPases) build up a proton gradient with hydrolysis of ATP. They can only be found in the vesicles of endocytosis and exocytosis as well as in lysosomes , endosomes and Golgi vesicles of eukaryotes and in the vacuoles of plants and yeasts . They control the pH in the vesicles. The resulting proton gradient is used to import and export other molecules. The ATPases represent a complex of 12 to 14 subunits: the VO complex forms the channel, the V1 complex protrudes into the cytosol and catalyzes the hydrolysis of ATP to ADP and phosphate. There is a structural similarity to the F-type.

ABC transporter

(TCDB 3.A.1 ) See the main article ABC-Transporter .

Sec proteins

(TCDB 3.A.5 ) See the main article Sec-System .

Sec transporters for preproteins are mainly found in bacteria, an important protein complex is further developed in eukaryotes, the Sec61 translocator in the endoplasmic reticulum (ER).

MPT proteins

(TCDB 3.A.8 ) Mitochondrial inner membrane import translocases are protein complexes that transport preproteins into the mitochondria of the eukaryotes.

ER-RT

(TCDB 3.A.16 ) Wrongly folded proteins are transported back from the endoplasmic reticulum into the cytosol by a so-called retrotranslocon for degradation in peroxisomes. The ATPase whose energy is used is called Derlin (gene: DERL ) in eukaryotes .

Vegetable membrane ATPases

(TCDB 3.A.9 ) In addition to the Sec proteins, plants also use so-called chloroplast envelope protein translocases (CEPT, Tic-Toc) to create preproteins in the chloroplasts.

Bacterial membrane ATPases

  • the arsenite and antimonite resistance efflux pumps ( 3.A.4 )
  • the type III secretion system for protein secretion in Gram-negative bacteria ( 3.A.6 )
  • the IVSP family in Gram-negative bacteria, which can pump proteins and DNA out of the cell into other cells (bacteria, yeast, plants) ( 3.A.7 )
  • the DNA T family for the uptake of single-stranded DNA in various types of bacteria ( 3.A.11 )
  • the S-DNA-T family for exporting DNA ( 3.A.12 )
  • the FPhE family for the export of filamentous phages ( 3.A.13 )
  • the FPE family for protein export ( 3.A.14 )
  • the MTB family for protein export ( e.g. pullulanase ) from gram-negative bacteria ( 3.A.15 )
  • the phage T7 injectisome family for DNA import ( 3.A.17 )

N-type ATPases

An N-type ATPase was found in addition to the F-type ATPase in Burkholderia pseudomallei . N-type ATPases can also pump Na + ions instead of H + ions ('protons'). The rotation mechanism is similar to the F, V and A types.

E-type ATPases

E-type ATPases (with E for 'extracellular') are membrane-bound enzymes on the cell surface with a wide range of tasks, such as the hydrolysis of other nucleoside triphosphates (NTPs) such as UTP instead of ATP.

Remarks

  1. ↑ In chemistry, protons always mean hydrogen ions H + . This does not exclude heavy hydrogen (deuterium) either, although in this case H + are, strictly speaking, deuterons . In addition, the H + ions are always hydrogenated to hydronium ions H 3 O + in aqueous solution . In terms of size, the hydronium ion corresponds roughly to a sodium ion Na + , which makes it understandable that in some cases 'protons' have been replaced by Na + .

Individual evidence

  1. ↑ V. Müller et al .: Structure and function of the A1A0-ATPases from methanogenic Archaea , in: J Bioenerg Biomembr. 31 (1): pp. 15–27 of February 1999, PMID 10340845 (incorrect A0 in the title instead of Ao)
  2. ↑ Armen Y Mulkidjanian, Michael Y Galperin, Kira S Makarova, Yuri I Wolf and Eugene V Koonin: Evolutionary primacy of sodium bioenergetics . In: Biology Direct . 3, No. 13, 2008. doi : 10.1186 / 1745-6150-3-13 .
  3. ↑ a b arms Y Mulkidjanian, Kira Makarova S, Y Michael Galperin, Eugene V Koonin: Inventing the dynamo machine: the evolution of the F-type and V-type ATPases . In: Nature Reviews Microbiology . 5, No. 11, 2007, pp. 892-899. doi : 10.1038 / nrmicro1767 . This article at Uni Osnabrück: Perspectives (PDF)  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.macromol.uni-osnabrueck.de  
  4. ↑ a b c Armen Y Mulkidjanian, Michael Y Galperin, Eugene V Koonin: Co-evolution of primordial membranes and membrane proteins . In: Trends Biochem Sci. . 4, No. 34, 2009, pp. 206-215. doi : 10.1016 / j.tibs.2009.01.005 . PMC 2752816 (free full text).  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.macromol.uni-osnabrueck.de  
  5. ↑ a b c Jennifer McDowall / Interpro: ATP Synthase: The ATPase-Family (English)
  6. ↑ Enas Qudeimat, Alexander MC Faltusz, Glen Wheeler, Daniel Lang, Colin Brownlee, Ralf Reski , Wolfgang Frank (2008): A PIIB-type Ca 2+ -ATPase is essential for stress adaptation in Physcomitrella patens. PNAS 105, 19554-19559. (On-line)
  7. ↑ Bioeconomy BW: A protein brings up stress from March 3, 2009
  8. ↑ Beyenbach KW, Wieczorek H: The V-type H + ATPase: molecular structure and function, physiological roles and regulation . In: J. Exp. Biol. . 209, No. Pt 4, February 2006, pp. 577-89. doi : 10.1242 / jeb.02014 . PMID 16449553 .
  9. ↑ S. Schulz, M. Wilkes, DJ Mills, W. Kühlbrandt, T. Meier: Molecular architecture of the N-type ATPase rotor ring from Burkholderia pseudomallei. In: EMBO reports. Volume 18, number 4, April 2017, pp. 526-535, doi : 10.15252 / embr.201643374 , PMID 28283532 , PMC 5376962 (free full text).
  10. ↑ DV Dibrova et al .: Characterization of the N-ATPase, a distinct, laterally transferred Na + -translocating form of the bacterial F-type membrane ATPase , in: Bioinformatics, Vol- 26, Issue 12, June 15, 2010, p 1473-1476, doi: 10.1093 / bioinformatics / btq234

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