A-ATP Synthase
From Proteopedia
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The P-Loop is the eight residue consensus sequence of amino acid <scene name='A-ATP_Synthase/P_loop_3p20/2'>residues 234-241</scene> '''G'''PFGS'''GKT''' . The P-loop or phosphate binding loop is conserved only within the A subunits and is a glycine rich loop preceded by a beta sheet and followed by an alpha helix. It interacts with the phosphate groups of the nucleotide and with a magnesium ion at residue K240 and T241, which coordinates the ?- and ?-phosphates. This P-loop has an arched conformation unique to A-ATP Synthase, indicating that the mode of nucleotide binding and the catalytic mechanism is different from that of other syntheses. <ref name= Priya> PMID: 21925186</ref> For example, in A-ATP Synthases <scene name='A-ATP_Synthase/P_loop_3p20/4'>F236</scene> is involved in P-Loop stabilization, but its equivalent (alanine) in subunit B of the F-ATP syntheses subunit beta is a key residue in the catalytic process in moving towards the y-phosphate of ATP during catalysis. By comparing the average distances of the alpha carbons of the P-loop residues to the sulfate, vanadate, and PNP molecules, it was found that the PNP molecule is closest, followed by the vanadate then the sulfate. [[grah]] | The P-Loop is the eight residue consensus sequence of amino acid <scene name='A-ATP_Synthase/P_loop_3p20/2'>residues 234-241</scene> '''G'''PFGS'''GKT''' . The P-loop or phosphate binding loop is conserved only within the A subunits and is a glycine rich loop preceded by a beta sheet and followed by an alpha helix. It interacts with the phosphate groups of the nucleotide and with a magnesium ion at residue K240 and T241, which coordinates the ?- and ?-phosphates. This P-loop has an arched conformation unique to A-ATP Synthase, indicating that the mode of nucleotide binding and the catalytic mechanism is different from that of other syntheses. <ref name= Priya> PMID: 21925186</ref> For example, in A-ATP Synthases <scene name='A-ATP_Synthase/P_loop_3p20/4'>F236</scene> is involved in P-Loop stabilization, but its equivalent (alanine) in subunit B of the F-ATP syntheses subunit beta is a key residue in the catalytic process in moving towards the y-phosphate of ATP during catalysis. By comparing the average distances of the alpha carbons of the P-loop residues to the sulfate, vanadate, and PNP molecules, it was found that the PNP molecule is closest, followed by the vanadate then the sulfate. [[grah]] | ||
| - | K240 and T241 are both contained within the P-Loop. Their behavior with regards to the molecules in the active site is not characteristic of the P-Loop movement as a whole. Mutations that changed K and T to alanine produced data consistent with the hypothesis that K20 stabilizes the transition state. | + | K240 and T241 are both contained within the P-Loop and are largely solvent exposed. Their behavior with regards to the molecules in the active site is not characteristic of the P-Loop movement as a whole. Mutations that changed K and T to alanine produced data consistent with the hypothesis that K20 stabilizes the transition state. Larger than average deviations were observed in the backbone structure of both mutants. Mutations in K240 causes the critical hydroxyl group of the S238 residue to orient in another direction. |
side chain changes. | side chain changes. | ||
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==Transition State Stabilization== | ==Transition State Stabilization== | ||
| - | Five steps inside the catalytic A-subunit are critical for catalysis. Substrate entrance, phosphate and nucleotide binding, transition-state formation, ATP formation, and product release. The [http://en.wikipedia.org/wiki/Vanadate vanadate] bound model mimics the transition state. [http://en.wikipedia.org/wiki/Orthovanadate Orthovandate] is a useful transition state analog because it can adapt both tetragonal and trigonal bipyramidal coordination geometry. The '''Avi''' structure can be compared to the '''As''' sulfate bound structure and the '''Apnp''' AMP-PNP bound structure. '''As''' is analogous to the phosphate binding (substrate) structure and '''Apnp''' is analogous to the ATP binding (product) structure<ref name= Manimekalai?> PMID:21396943</ref>. The movement of specific residues to stabilize the transition state is demonstrated by comparing the deviations between the three structures. [[pic]] Although not at bonding distances the residues | + | Five steps inside the catalytic A-subunit are critical for catalysis. Substrate entrance, phosphate and nucleotide binding, transition-state formation, ATP formation, and product release. The [http://en.wikipedia.org/wiki/Vanadate vanadate] bound model mimics the transition state. [http://en.wikipedia.org/wiki/Orthovanadate Orthovandate] is a useful transition state analog because it can adapt both tetragonal and trigonal bipyramidal coordination geometry. The '''Avi''' structure can be compared to the '''As''' sulfate bound structure and the '''Apnp''' AMP-PNP bound structure. '''As''' is analogous to the phosphate binding (substrate) structure and '''Apnp''' is analogous to the ATP binding (product) structure<ref name= Manimekalai?> PMID:21396943</ref>. The movement of specific residues to stabilize the transition state is demonstrated by comparing the deviations between the three structures. [[pic]] Although not at bonding distances the residues P233 G234 L417 stabilize the vandate in the transition state with weak nonpoalr interactions, and residues K240 and T241 stabilize with polar interactions. move closer to the vanadate with respect to the two other structures and are proposed to stabilize the transition state during catalysis. The transition state is also stabilized by weak interactions between the charged K162+ R189+ E188 |
Residue <scene name='A-ATP_Synthase/238/1'>S238</scene> is a polar serine molecule that interacts with the nucleotides via a hydrogen bond during catalysis, and binds the vandate in the intermediate structure. The distance between residue S238 is longest in '''As''', shortest in '''Avi''' and intermediate in '''Apnp''' . In '''As''' a water molecule bridges the gap, which is removed in '''Avi'''. Dehydration of the transition state active site is reversed when ATP forms. In '''Apnp''' the water molecule interacts with the y-phosphate of ATP. | Residue <scene name='A-ATP_Synthase/238/1'>S238</scene> is a polar serine molecule that interacts with the nucleotides via a hydrogen bond during catalysis, and binds the vandate in the intermediate structure. The distance between residue S238 is longest in '''As''', shortest in '''Avi''' and intermediate in '''Apnp''' . In '''As''' a water molecule bridges the gap, which is removed in '''Avi'''. Dehydration of the transition state active site is reversed when ATP forms. In '''Apnp''' the water molecule interacts with the y-phosphate of ATP. | ||
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<ref name= Manimekalai?> PMID:21396943</ref> | <ref name= Manimekalai?> PMID:21396943</ref> | ||
| - | The second vandate is positioned in a region exactly opposite the nucleotide-binding site, where the ATP molecule transiently associates on its way to the final binding pocket in subunit "'B"'. [L417] Is involved in a bifurcated hydrogen bond with the second vandate. Similar binding behavior was observed for "'As"' indicating that the substrate molecule has a similar path of entry to the active site in both the "'A"' and '"B"' subunit of the A-ATP synthase and that they have a transient binding position near the P-Loop. It is proposed that Pi binds first to the catalytic site and sterically hinders ATP binding, thereby selectively allowing binding of ADP. The "'Avi"' structure confirms this, since although both ADP and Vi were present in the crystallized solution, the catalytic A-subunit first permits only the binding of the phosphate analogue Vi. Hence the present "Avi"' structure represents a trapped initial transition state showing for the first time both the entering path and the final Vi-bound state in the catalytic subunit. | + | The second vandate is positioned in a region exactly opposite the nucleotide-binding site, where the ATP molecule transiently associates on its way to the final binding pocket in subunit "'B"'. [L417] Is involved in a bifurcated hydrogen bond with the second vandate. This vanadate is also stabilized by weak non polar interactions with P233 F399 F414 A416 and A419, as well as polar interactions with D418 N431 and T424. Similar binding behavior was observed for "'As"' indicating that the substrate molecule has a similar path of entry to the active site in both the "'A"' and '"B"' subunit of the A-ATP synthase and that they have a transient binding position near the P-Loop. It is proposed that Pi binds first to the catalytic site and sterically hinders ATP binding, thereby selectively allowing binding of ADP. The "'Avi"' structure confirms this, since although both ADP and Vi were present in the crystallized solution, the catalytic A-subunit first permits only the binding of the phosphate analogue Vi. Hence the present "Avi"' structure represents a trapped initial transition state showing for the first time both the entering path and the final Vi-bound state in the catalytic subunit. |
Revision as of 17:37, 17 November 2011
Introduction
The archaeal A1A0 ATP synthase represent a class of chimeric ATPases/synthase , whose function and general structural design share characteristics both with vacuolar V1V0 ATPases and with F1Fo ATP synthases [1]. A1A0 ATP synthase catalyzes the formation of the energy currency ATP by a membrane-embedded electrically-driven motor. The archaeon in this study,Pyrococcus horikoshii OT3 is an anaerobic thermophile residing in oceanic deep sea vents with an optimal growth temperature of 100degrees. Anaerobic fermentation is its principle metabolic pathway. The specific enzymatic process in A-ATP synthase reveals novel, exceptional subunit composition and coupling stoichiometries that may reflect the differences in energy-conserving mechanisms as well as adaptation to temperatures at or above 100 degrees C. Because some archaea are rooted close to the origin in the tree of life, these unusual mechanisms are considered to have developed very early in the history of life and, therefore, may represent the first energy-conserving mechanisms. [2]
Structure
A-ATP synthase ATP synthase is composed of two parts A1 and A0 which are composed of at least nine subunits A3B3C:D:E:F:H2:a:cx that function as a pair of rotary motors connected by central and peripheral stalk(s) [2].This structure is similar to the known structure of F ATP synthase. The A0 domain is the hydrophobic membrane embedded ion-translocating sector that uses the H+ gradient to power ATP synthase in domain A1. A1 is catalytic and water soluble containing A and B subunits. These subunits are comparable to F-ATP synthase ATP synthase alpha/beta subunits. The A subunit of A1 is catalytic and the B subunit is regulatory, with a substrate-binding site on each.
Significance
The active site is continually reshaped by interactions with the substrate as the substrate interacts with the enzyme. As a result, the substrate does not simply bind to a rigid active site; the amino acid side chains which make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function. Stabilization of the transition state supports the induced fit model. A-ATP synthase lowers the activation energy by creating an environment in which the transition state is stabilized
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References
- ↑ Schafer IB, Bailer SM, Duser MG, Borsch M, Bernal RA, Stock D, Gruber G. Crystal structure of the archaeal A1Ao ATP synthase subunit B from Methanosarcina mazei Go1: Implications of nucleotide-binding differences in the major A1Ao subunits A and B. J Mol Biol. 2006 May 5;358(3):725-40. Epub 2006 Mar 10. PMID:16563431 doi:http://dx.doi.org/10.1016/j.jmb.2006.02.057
- ↑ 2.0 2.1 Muller V, Lemker T, Lingl A, Weidner C, Coskun U, Gruber G. Bioenergetics of archaea: ATP synthesis under harsh environmental conditions. J Mol Microbiol Biotechnol. 2005;10(2-4):167-80. PMID:16645313 doi:10.1159/000091563
- ↑ Priya R, Kumar A, Manimekalai MS, Gruber G. Conserved Glycine Residues in the P-Loop of ATP Synthases Form a Doorframe for Nucleotide Entrance. J Mol Biol. 2011 Sep 8. PMID:21925186 doi:10.1016/j.jmb.2011.08.045
- ↑ 4.0 4.1 Manimekalai MS, Kumar A, Jeyakanthan J, Gruber G. The Transition-Like State and P(i) Entrance into the Catalytic A Subunit of the Biological Engine A-ATP Synthase. J Mol Biol. 2011 Mar 16. PMID:21396943 doi:10.1016/j.jmb.2011.03.010
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