Atp synthase , Atp synthase complex 1 to 4.

It is a collection of membrane-embedded proteins and organic molecules, most of them organized into four large complexes labeled I to IV.
The resulting proton gradient is used by the ATP synthase complex for ATP formation.
ATP synthesis is driven by the return of protons to the matrix through an integral membrane protein complex known variously as ATP synthase.

1. STRUCTURE OF ATPase COMPLEX-V 1

2. INTRODUCTION During cellular respiration, organic compounds are oxidized to generate usable chemical energy in the form of ATP. The respiratory electron transport chain (ETC) of mitochondria is at the center of this process. The respiratory electron transport chain (ETC) couples electron transfer from organic substrates onto molecular oxygen with proton translocation across the inner mitochondrial membrane. 2

3. It is a collection of membrane-embedded proteins and organic molecules, most of them organized into four large complexes labeled I to IV. The resulting proton gradient is used by the ATP synthase complex for ATP formation. ATP synthesis is driven by the return of protons to the matrix through an integral membrane protein complex known variously as ATP synthase. 3

4. In 1960 the American scientist Efraim Racker and co-workers isolated, from mitochondria, the enzyme “F0 F1 ATPase” which we now call ATP synthase. 4

5. ATP SYNTHASE This is one of the most conserved proteins in Bacteria, Plants and Mammals. This enzyme is the smallest known biological nanomotor and plays a crucial role in ATP generation. The enzymes are essentially the same in structure and function as those from mitochondria of animals, plants and fungi, and the chloroplasts of plants. 5

6. TYPES OF ATPase There are three classes of ATPases , which differ in structure and the type of ion that they transport; 6

7. ATPase (complex v) IN PLANTS ATP synthase is a protein that is responsible for the generation of ATP through phosphorylation of ADP by using electrochemical energy generated by proton gradient across the inner membrane of mitochondria. These are protein clusters. In plant cells, ATP synthase complex resides in a inner mitochondrial membrane and thylakoid membrane. ADP phosphorylation occurs in this complex, resulting in the synthesis of ATP molecules during photosynthesis. 7

8. FUNCTION OF ATP SYNTHASE The enzyme ATP synthase has diverse functions. ATP synthase function includes: Synthesizing ATP molecules to provide organisms with an abundant high-energy source. It acts as the powerhouse of the cell by synthesizing ATP. It can also operate in the reverse direction, hydrolysing ATP and pumping protons under certain conditions.
It pumps protons outside during hydrolytic activity, whereas the protons may pass inside through the ATPase during synthetic activity. 8

9. STRUCTURE OF ATP SYNTHASE ATP synthase is a large mushroom-shaped asymmetric protein complex. The mitochondrial ATP synthase is a multi-subunit protein complex having an approximate molecular weight of 550 kDa . It has two subunits, F0 unit (rotational) F1 unit (catalytic) 9

10. F1 COMPONENT F1 (factor 1) component projects into the matrix from the inner membrane. It is hydrophilic region. F1 unit functions as the active centre . John Walker deduced the high-resolution structure of the F1 part of ATP synthase enzyme and jointly owned the Nobel Prize with Paul Boyer in 1997 in chemistry. Mitochondrial F1 has nine subunits of five different types, Three α subunits Three β subunits Single γ subunit Single δ subunit Single ε subunit 10

11. Alpha (α) subunit : promotes activity of beta. Beta (β) subunits : Catalytic site for ATP synthesis. Gamma (γ) subunit : Forms the central stalk connects F0 with F1 Delta (δ) subunit : Holds a, β hexamer in a fixed position Epsilon (ε) subunit : Attach γ subunit with C10 ring 11

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13. ALPHA AND BETA SUBUNIT In F- ATPases , there are three copies each of the alpha and beta subunits that form the catalytic core of the F1 complex, while the remaining F1 subunits (gamma, delta, epsilon) form part of the stalks . There is a substrate-binding site on each of the alpha and beta subunits, those on the beta subunits being catalytic , while those on the alpha subunits are regulatory . The alpha and beta subunits form a cylinder that is attached to the central stalk. 13

14. The beta subunits undergo a sequence of conformational changes leading to the formation of ATP from ADP, which are induced by the rotation of the gamma subunit , itself is driven by the movement of protons through the F0 complex C subunit. The structure of the alpha and beta subunits is almost identical. Each subunit consists of a N-terminal β-barrel, a central domain containing the nucleotide-binding site and a C-terminal α bundle domain of 7 and 6 helices, respectively, in the alpha and beta subunits . Each of the three β subunits has one catalytic site for ATP synthesis. The knob like portion of F1 is a flattened sphere, 8 nm high and 10 nm across, consisting of alternating α and β subunits arranged like the sections of an orange. 14

15. The α lpha and β-subunits arranged in an alternating manner (αβαβαβ) to form a hexameric ring with the γ-subunit at its center. There are six nucleotide-binding sites at the interfaces between the α- and β-subunits. Three of the nucleotide-binding sites are catalytically active, whereas the other three nucleotide-binding sites are not catalytically active. The three catalytically active sites are mainly encompassed by the β-subunits and therefore are termed the β-subunit sites. 15

16. The ATPase F1 complex gamma subunit forms the central shaft that connects the Fo rotary motor to the F1 catalytic core. The gamma subunit functions as a rotary motor inside the cylinder formed by the alpha(3)beta(3) subunits in the F1 complex. The best-conserved region of the gamma subunit is its C terminus, which seems to be essential for assembly and catalysis. The δ and ε subunits of F1, form a leg -and-foot that projects from the bottom side of F1 and stands firmly on the ring of c subunits. 16

17. F0 COMPONENT The second component of ATP synthase. It is the Hydrophobic region. It spans the inner mitochondrial membrane. F0 unit is composed of four polypeptide chains. All the polypeptides of the F0 unit are of same kind. F0 is a specific protein factor which when added to the F1 results in the inhibition of the ATP synthase activity by Oligomycin . Hence F0 is also called oligomycin sensitivity conferring factor or OSCF. There is a channel through F0 that specifically translocates protons on both sides. 17

18. The Fo complex making up the proton pore is composed of three subunits, a, b, and c. a subunit – 1 b subunit – 2
c subunit – 10 to 12 Subunit a: forms proton channel Subunit b: forms peripheral stalk connects F0 with F1. Subunit c is a small, very hydrophobic polypeptide, consisting almost entirely of two trans-membrane helices, with a small loop extending from the matrix side of the membrane. 18

19. Biochemical and mutational experiments have shown that the a and c subunits contain functional groups that are necessary for proton translocation through the membrane. The a & b subunits align the exterior of the multimeric c subunits. The cavity in between a and c subunits providing the pathway for protons. Protonation and deprotonation in this interface is thought to cause rotation of the c ring thereby rotating the gamma subunit. The synthesis of ATP requires 120 degrees. In certain some synthases with a 9 c subunit ring require 3 proton translocations.
In other synthases with a 10 c subunit ring require 4 proton translocations 19

20. The Fo portion of the ATP synthase comprises the proton turbine as well as the base of the stator. The core of Fo is composed of an oligomer of the c-subunits, which contain an essential carboxylate from the side chain of either a glutamate or aspartate residue. The side chain carboxyl acts as the proton donor and acceptor in proton translocation pathway. 20

21. Rotor The C9-12 complex along with the ƴ and ε constitute the moving unit, i.e. rotor. It undergoes rotational motion, as the protons or H+ ions move across the thylakoid membrane. Due to the rotary mechanism, ATP synthase is also termed as molecular machine. Stator The B2 and a subunit along with the α3 β3 δ complex, makes up the stationary unit, i.e. stator. The stator is also referred to as the peripheral or extrinsic stalk. The stator functions to hold F1 fixed to allow rotation of the rotor within the core of F1. The stator provides a structural support and is not involved directly in the catalytic reaction. 21

22. Central stalk It is Considered part of the Fo rotor, it connects the Fo and F1 motors together. The central stalk of mitochondrial ATP synthase consists of subunits γ, δ, and ε, and along with the membraneous subunit c oligomer constitutes the rotor domain of the enzyme. 22

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24. Inhibitor of Mitochondrial ATP Synthase ATP synthesis in chloroplast and mitochondria can be inhibited by the destruction of ATP synthase in mitochondria, there are some examples of such inhibitor of mitochondrial ATP synthase Aurovertin - It inhibits the F1 domain of the ATP synthase.Each β subunit contains one aurovertin binding site . Oligomycin – It inhibits the Fo domain of the enzyme.Oligomycin is a competitive inhibitor Ventriuricidin - It inhibits the Fo domain of the chloroplast ATP synthase DCCD- It blocks the proton flow through the form of mitochondrial and chloroplast ATP synthase. 24

25. REFERENCE Hopkins, G., William. (1995). Introduction To Plant Physiology. John Wiley and Sons, Inc.
Ghosh, A.K., Mukherji , S. (1996). Plant Physiology. New Central Book Agency Pvt. Itd . Verma , V (2007). Textbook of Plant Physiology (4 th ed ). Thomson Asia Pvt.ltd , Singapore. https://study.com/academy/lesson/atp-synthase-definition-structure-function.html https://microbiochem.weebly.com/structure-and-mechanism-of-atp-synthase.html https://biologyreader.com/atp-synthase-in-photosynthesis.html 25