Acetylcholine receptor, Shraddha Godke, Loaded by Dr Anthony

Views:
 
Category: Education
     
 

Presentation Description

Presentation on acetylcholine receptor by Shraddha Godke, loaded by Dr Anthony Crasto, helping millions

Comments

By: anthonycrasto1964 (71 month(s) ago)

great

Presentation Transcript

PowerPoint Presentation:

29 November 2011 --Loaded by Dr Anthony Crasto , helping millions 1 PRESENTED BY, MISS. SHRADDHA S. GHODKE. Second semester, M. Pharmacy Dept. of Pharmaceutical Chemistry GUIDED BY, Dr. A.R. CHABUKSWAR Dept. of Pharmaceutical Chemistry ACETYLCHOLINE RECEPTOR MAHARASHTRA INSTITUTE OF PHARMACY , PUNE A SEMINAR ON

PowerPoint Presentation:

29 November 2011 2 Contents:- Introduction - Receptor & messenger - Receptor model Acetylcholine & its receptors - Biosynthesis, hydrolysis of Ach - SAR & receptor binding Mapping of Muscarinic receptor Stereochemistry of Ach Current Muscarinic receptor model

PowerPoint Presentation:

29 November 2011 3 Computer assisted molecular modeling Subtypes of Muscarinic receptor Muscarinic agonist Muscarinic antagonist Nicotinic receptor Receptor model - subtypes - Agonist - Antagonist Literature survey Conclusion Bibliography

PowerPoint Presentation:

29 November 2011 4 INTRODUCTION: “Receptor and messengers”: Receptors : which receives the messenger and causes response. A receptor is a protein molecule embedded within a cell membrane with part of its structure facing the outside of the cell. The protein surface is a complicated shape containing hollows, ravines, ridges & an area which has the correct shape to accept the incoming messenger. This area is known as binding site. Cell M B R Cell membrane message M: Messenger R: Receptor B: Binding site Fig . Binding of a messenger to a receptor

PowerPoint Presentation:

29 November 2011 5 Receptor Models : - Ion Channel Receptors: e.g. Nicotinic Ach Receptor , GABA A Receptor, Glutamate Receptor, GABA C Receptor 2. G - Protein Receptors: e.g. Adrenergic Receptor, Muscarinic Ach Receptor , GABA B Receptor Kinase Linked Receptors: e.g. Insulin Receptor Nuclear Receptors: e.g. Steroid hormone, Thyroid hormone Receptor

PowerPoint Presentation:

29 November 2011 6 ACETYLCHOLINE AND IT’S RECEPTORS Ach is 100,000 times more potent than choline in producing biological activity. Ach choline

PowerPoint Presentation:

29 November 2011 7 2. Nicotinic Receptor : so named because they specifically stimulated by Nicotine ( present in tobacco ) Nicotine Actions are mediated through receptors present on the effectors cells. 1. Muscarinic Receptor: so named because they specifically stimulated by Muscarine ( the active principle of a poisonous mushroom ) L (+) Muscarine

PowerPoint Presentation:

29 November 2011 8 synthesis, storage, and release of acetylcholine (ACh) :- Acetylcholine as a messenger

PowerPoint Presentation:

29 November 2011 9 L-serine choline Acetylcholine ethanolamine

PowerPoint Presentation:

29 November 2011 10 Acetylcholine choline + acetate

PowerPoint Presentation:

29 November 2011 11 Ach - Structure, SAR, &receptor binding Acyloxy group Ethylene group Quaternary ammonium group The positively charged nitrogen atom : Essential to activity. Distance from N to ester group : Rule of Five by led Ing. Ester functional group : Important. Ethylene bridge between N & ester : Cannot be extended. Methyl group on nitrogen : At least 2 essential, 3 rd tolerated, more than 1 large group leads to loss activity. SAR:

PowerPoint Presentation:

29 November 2011 12 Acetylcholine CH3 H : readily hydrolysed by Achesterase Carbachol NH2 H : readily not hydrolysed by Achesterase Methacholine CH3 CH3 : (CH3-beta to Quaternary Nitrogen) - Increase Muscarinic activity, - No Nicotinic activity. Bethanechol NH2 CH3 : readily not hydrolysed by Achesterase - Increase Muscarinic activity, - No Nicotinic activity. Fig. Chemical structures of the choline esters.

PowerPoint Presentation:

29 November 2011 13 SAR relationship have made it possible to MAP the receptor and prepare a MODEL that can account for the affinity& the intrinsic activity of cholinergic agonist. Early attempts to map the cholinergic receptor showed the importance to muscarinic potency of the Quat.amine and the Ester group separated by 2-C.

PowerPoint Presentation:

29 November 2011 14 Esteratic site Anionic site Mapping of Muscarinic receptor Fig. Original representation of the Muscarinic receptor. + _ + Muscarinic receptor N O O CH3 CH2 CH2 CH3 CH3 CH3 C Ester grouping Alkyl amine chain Cationic head

PowerPoint Presentation:

29 November 2011 4JUNE 2008 15 This model state ionic bonding of Ach to receptor by: Electrostatic interaction between +ve charge Quat.N and -ve charge anionic site . ------ H O - _ _ + Anionic site Esteric site The –ve charge due to carboxyl group of dicarboxylic amino acid ( aspartate or glutamate ). H – bond between the ester O of Ach and OH group by esteric site of receptor.

PowerPoint Presentation:

29 November 2011 16 But, for muscarinic (M) agonists, it failed to explain: At least 2 of the alkyl groups bonded to Quat. N must be –CH3 grp . The known stereochemical requirements for agonist binding to the receptor. Fact that all potent cholinergic agonists have only 5 atoms between Q. N and terminal H. (Ing’s rule of five). 1 2 3 4 5

PowerPoint Presentation:

29 November 2011 17 Some scientists proposed that the M receptor and Achesterase were the same entity. This proposal was dispelled by experiment that interaction of cholinergic ligands with M receptor did not lead to chemical change of ligand i.e. hydrolysis. Ach receptor : agonist activity Achesterase : hydrolysis

PowerPoint Presentation:

29 November 2011 18 Subsequent models of M receptor depicted the receptor as a binding site on a protein molecule and explained more completely the structural and stereochemical requirements for cholinergic agonist activity. Binding studies between Ach analogs with varying number of CH 3 groups on nitrogen & AchE indicate that only two of the CH 3 groups are involved in the binding of the cholinergic ligand. Such a groups are bound to the receptor by both hydrophobic and van der waals forces. The presence of van der Waals forces implies a close fit of the molecule to the receptor. Similar studies with the following series of compound showed that as chain increases from C 2 H 5 through C 4 H 9 , C 5 H 11 there is a constant increase in energy liberated per mole of a drug as it is bound to enzyme or receptor.

PowerPoint Presentation:

29 November 2011 19 The energy liberated is that expected from the hydrophobic bond between each CH 2 group to the receptor. The energy changes between changing C 2 H 5 group by C 4 H 9 & C 5 H 11 can not accounted for a hydrophobic bond. This is because assuming that the terminal CH 3 group is held by both hydrophobic and van der Waals forces. Thus larger molecules fails to induce such a perfect fit.

PowerPoint Presentation:

29 November 2011 20 Hydrophobic forces (van der waals forces) Ionic bond Hydrophobic forces H- bonding But this model fails to consider the size and shape of the receptor. Rule of 5 limits on size of the receptor, but its value is limited unless the conformation assume by Ach when binding to the receptor is consider.

PowerPoint Presentation:

29 November 2011 21 Stereochemistry of Ach:- Early models for cholinergic receptor did not account for the observed stereo selectivity of the receptor for agonist and antagonist. Even though Ach dose not exhibit optical isomerism but many synthetic & naturally occurring agonists and antagonists are optical isomers. One of the enantiomer is many times more active than other. Thus the stereochemistry of cholinergic ligands is important for receptor binding. The stereochemistry of cholinergic ligands provides rational basis for design of cholinergic drugs as well as to describe properties and function of cholinergic receptors.

PowerPoint Presentation:

29 November 2011 22 Conformation of Ach:- Because of free rotation around most covalent bonds, Ach and its analogs can exist in many favorable conformations. The two structures below represents extremes in possible conformations. Quasi-ring conformation Extended conformation

PowerPoint Presentation:

29 November 2011 23 This conformations are illustrated by Newman projection as:-

PowerPoint Presentation:

29 November 2011 24 Expected conformation from the molecular models by minimizing bond overlap is antiperiplaner conformation. The techniques used to determine the thermodynamically preferred conformation of Ach as According to NMR studies- Preferred conformation of Ach (in aq. Solution) is synclinal (gauche or skew). It is supported by x-ray data (in solid , crystalline state) is also synclinal. Molecular orbital calculations also resulted in preferred conformation is synclinal. There is an intra molecular interaction, most probably an electrostatic attraction between Quaternary nitrogen and Carbonyl oxygen which stabilizes the synclinal conformation.

PowerPoint Presentation:

29 November 2011 25 But this may not be the conformation preferred by the receptor. In recognition of this possibility, Armstrong and colleagues synthesized & evaluated Muscarinic and Nicotinic activity of cis and trans isomers of conformationally rigid model of Ach. Cis & trans 2- Acetoxy cyclopropyl- 1-trimethyl ammonium iodide (ACTM). Because this model is based on a cyclopropane ring, ester and Quaternary nitrogen can’t change their relative position by bond rotation. Cis ACTM Trans ACTM

PowerPoint Presentation:

29 November 2011 4JUNE 2008 26 Cis isomer similar to syn periplanar conformation of Ach. Trans isomer approximates the anticlinal conformation.

PowerPoint Presentation:

29 November 2011 4JUNE 2008 27 Observation:- The (+) trans enantiomer is more potent than Ach at muscarinic receptor and much more potent than (-) Trans enantiomer. Racemic mixture of cis compound has no activity at muscarinic receptor. All are very weak nicotinic agonists. Conclusion:- Ach is most probably interact with muscarinic receptor in its less favored anticlinal conformation. The most active isomer (+) trans of cyclopropane analog have a torsion angle-137 o C (anticlinal) between ester oxygen and quaternary nitrogen. This significantly differ from 60 o C torsion angle in synclinal conformation (preferred by NMR & X-ray determination).

PowerPoint Presentation:

29 November 2011 4JUNE 2008 28 Current Muscarinic Receptor model:- Cloning and base sequencing of the genes encoding for muscarinic receptor are major advances in understanding chemical nature and functions of receptor. This experiment state that muscarinic receptor belong to group of receptor that are coupled to ‘guanine nucleotide binding proteins’ i.e. ‘G- protein coupled receptors (GPCR)’. Applications of Molecular Modeling:- This programme which deduce structure of muscarinic GPCR suggest that they are components of cell membrane and consists of seven trans membrane helical domains that are hydrophobic. It also contains 4 extracellular (E1-E4) and 4 intracellular(C1-C4) hydrophilic domains. The N- terminus of the GPCR protein is extracellular and C- terminus is intracellular.

PowerPoint Presentation:

29 November 2011 4JUNE 2008 29 G - Protein Receptors

PowerPoint Presentation:

29 November 2011 30 Computer Assisted Molecular Modeling:- It made possible to obtain 3 dimensional models of muscarinic receptor. A proposed top view model of M-1 receptor. 2 1 3 D105 4 5 T189 Y381 6 7 Circle represents 7 TM domains D105 - aspartate, T189 – Threonoine, Y381 – Tyrosine residues Diagram:- Model of Ach interaction with M-1 Receptor

PowerPoint Presentation:

29 November 2011 31 The current Model for Muscarinic Receptor:- In this model agonist binds to muscarinic receptor located in cell membrane. This ligand- receptor interaction is translated by conformational perturbation through the receptor protein to receptor coupled G protein.

PowerPoint Presentation:

29 November 2011 32 In this proposal G protein is composed of 3 subunits ( α , β , γ) Which link the receptor to effector, which produce 2 nd messenger molecules within the cell. G-protein is in inactive state with GDP bound to it’s α subunit. Upon interaction of agonists with muscarinic receptor α subunit releases the GDP & binds to GTP. The α subunit GTP complex then dissociates from β γ subunits. Both subunit GTP complex and β γ subunits interact with membrane bound effectors as 1) Phospholipase C, 2) Adenylate cyclase or 3) Ion channels (K + & Ca +2 )

PowerPoint Presentation:

29 November 2011 33 α β γ GTP α β γ GTP α β γ GDP α β γ GDP + + R Ach α subunit GTPase activity Diagram of the GTPase cycle and subunit association/dissociation proposed to control signal transduction between muscrinic GPCR and the effector. GDP GTP

PowerPoint Presentation:

29 November 2011 34 Muscarinic receptor subtypes:- Subtypes are based on their Pharmacologic responses to various ligands. These are M 1 , M 2 , M 3 , M 4 and M 5 . But only four types are distinguish functionally and Pharmacologically. Genetic differences:- Advances in molecular biology led to cloning of cDNAs that encode for receptors. These designated as m 1 , m 2 , m 3 , m 4 and m 5 . The comparison of these Muscarinic subtypes are as shown in following table:-

PowerPoint Presentation:

29 November 2011 35 Subtypes of M- receptor M 1 Neural M 2 Cardiac M 3 Glandular, smooth muscles M 4 M 5 Main location CNS, Gastric & salivary glands Heart , GIT, CNS Gastric & salivary glands, GIT, Eye CNS CNS Cellular response Increase IP 3 , DAG, Depolarization, excitation, increase potassium conductance Decrease in a) cAMP inhibition, b) Ca ++ conductance, Increase K + conductance Increase IP 3 , Ca ++ conductance, As M 2 As M 3 Functional responces CNS excitation, gastric secretion Cardiac inhibition, neural inhibition Gastric & saliva secretion, GI smooth muscle contraction, occular accomodation Enhanced locomotion Not known

PowerPoint Presentation:

29 November 2011 36 Subtypes of M- receptor M 1 Neural M 2 Cardiac M 3 Glandular, smooth muscles M 4 M 5 Agonists (non-selective, except those in italics) ACh Carbachol Oxotremorine As M1 As M1 As M1 As M1 Antagonists (non-selective, except those in italics) Atropine Dicycloverine* (dicyclomine) Tolterodine Oxybutynin Ipratropium Pirenzepine Atropine Dicycloverine Tolterodine Oxybutynin Ipratropium Gallamine Atropine Dicycloverine Tolterodine Oxybutynin Ipratropium Atropine Dicycloverine Tolterodine Oxybutynin Ipratropium Mamba toxin MT3 Atropine Dicycloverine Tolterodine Oxybutynin Ipratropium

PowerPoint Presentation:

29 November 2011 37

PowerPoint Presentation:

29 November 2011 38 Muscarinic Agonists:- M Agonist R2 R1 Therapeutic use Carbacol NH2 H To treat postoperative intestinal atony Retention of urine. Methacholine CH3 CH3 To treat abdominal distention.

PowerPoint Presentation:

29 November 2011 39 Therapeutic use: • Used in the treatment of glaucoma and xerostomia (dry mouth). PILOCARPINE

PowerPoint Presentation:

29 November 2011 40 Future Muscarinic Agonists: Current research interest is focused on developing agents with selective affinity. for muscarinic receptors in the brain. Potentially useful in the treatment of Alzheimer’s disease and other cognitive disorders. ARECOLINE

PowerPoint Presentation:

29 November 2011 41 OXOTRIMORINE

PowerPoint Presentation:

29 November 2011 42 Muscarinic antagonist:- These compounds have high binding affinity for muscarinic receptor but have no intrinsic activity. When the antagonists binds to the receptor, the receptor protein undergoes a conformational perturbation that is different from that produced by an agonist. Therefore antagonists binding to the receptor produces no response. Therapeutic applications:- Decrease contractions of smooth muscles of GIT & UT - and thus they used in treatment of smooth muscle spasms. Dilation of pupils:- Used in ophthalmologic examinations. (contraindicated in Glaucoma). Decrease gastric secretion:- In treatment of gastric ulcer.

PowerPoint Presentation:

29 November 2011 43 SAR of Muscarinic antagonists:- Muscarinic antagonists must compete with agonists for a common receptor. Their ability to do this effectively is because the large groups R1 & R2 enhance binding to the receptor. As the antagonists are larger than agonists, R1 & R2 bind outside the binding site of Ach.

PowerPoint Presentation:

29 November 2011 44 Hypothetical models for the binding of muscarinic antagonist to the Muscarinic receptor. Classical view of binding of lachesine to the muscarinic receptor .

PowerPoint Presentation:

29 November 2011 45 Specific agents Atropine :- Here the amine group is separated from the ester oxygen by more than two carbons still the conformation by tropanol ring remains such that the intervening distance is similar to that of Ach. Proposed receptor-bound conformation of Atropin e and its interaction with mAChR.

PowerPoint Presentation:

29 November 2011 46 Nicotinic receptors:- Nicotinic receptors based on different anatomic sites 1) autonomic ganglia 2) Skeletal neuromuscular junction. Ach nicotinic receptors belongs to a group of receptor as ligand gated ion channel receptors. The receptor creates a trans membrane ion channel (the gate) & Ach (the Ligand) as a gate keeper. Ligand by interacting with the receptor to modulate the passage of ions, principally K + and Na + through the channel.

PowerPoint Presentation:

29 November 2011 47 Ach (gate keeper) ions Gate

PowerPoint Presentation:

29 November 2011 48 A nicotinic receptor was the first neurotransmitter receptor to be isolated andpurified in an active form using the molecular biological techniques. The nicotinic receptor of muscle tissue is a glycoprotein consisting of 4 distinct subunits α , β , γ and δ. In a single receptor molecule there is a pentameric arrangement of 2 α subunits, abbreviated α 2 β γ δ. The 5 subunits of each receptor protein are arranged around a central pore that serves as a ion channel.

PowerPoint Presentation:

29 November 2011 49 Based on molecular modeling, it is proposed that each subunit ( α , β , γ and δ) possess a hydrophilic extra cellular N- terminus, a hydrophilic intra cellular C- terminus & 4- alpha helical hydrophobic domains (M1, M2, M3, M4) that are in the cell membrane. (as in fig.)

PowerPoint Presentation:

29 November 2011 50 It has been suggested that these 5 amphipathic domains make up the walls of the ion channel in pentameric arrangement of the receptor subunits. There are two Ach binding sites on the extra cellular domain of each receptor molecule. One binding site is located on each α - subunit at the α - γ and α – δ interfaces.

PowerPoint Presentation:

29 November 2011 4JUNE 2008 51

PowerPoint Presentation:

29 November 2011 52 Sub-Types: Based on location as: N 1 (somatic) or Muscle receptor, N 2 (neural) or Ganglionic receptor. N 1 : Muscle receptors are confined to the skeletal neuromuscular junction. N 2 : Gaglionic receptors are responsible for transmission at sympathatic parasympathetic ganglia.

PowerPoint Presentation:

29 November 2011 53 Nicotinic agonist : Nicotin 2.Acetylcholine CH3 H : readily hydrolysed by Achesterase 3.Carbachol NH2 H : readily not hydrolysed by Achesterase 1.

PowerPoint Presentation:

29 November 2011 54 Nicotinic Antagonists: Agents that bind to cholinergic nicotinic receptors but do not have efficacy. Competitive antagonists. Two subclasses: 1. Skeletal neuromuscular blocking agents, 2. Ganglionic blocking agents. Skeletal neuromuscular blocking agents: Therapeutic Use : As a muscle relaxant in various surgical procedures.

PowerPoint Presentation:

29 November 2011 55 2. Ganglionic blocking agents: Therapeutic Use : No clinical use Ganglionic blocking drugs, because of their many side effects,like postural hypotention which can cause fainting are now clinically obsolete.

PowerPoint Presentation:

29 November 2011 4JUNE 2008 56 Literature review :

PowerPoint Presentation:

29 November 2011 57 Conclusion:- Our understanding & knowledge of the muscarinic and nicotinic receptors has advanced tremendously from the time these receptors were only ethereal concepts. Thanks to the dedicated efforts of many scientists . This understandings of cholinergic receptors provides the basis for the rational design of new selective therapeutic agents to treat diseases associated with cholinergic neurons.

PowerPoint Presentation:

29 November 2011 58 Bibliography : 1.WILLIAM O. FOYE, Principles of medicinal chemistry,Third edition, Varghese publishing house,1989, P: 119-27, 323-40. 2.DAVID A. WILLIAMS,THOMAS L.LEMKE, FOYE’S Principles of medicinal chemistry, Fifth edition, Lippincott Williams and wilkins, P: 264-88. 3.JOHN H. BLOCK, JOHN M. BEALE,Jr., Wilson & Gisvold’s Textbook of organic medicinal and pharmaceutical chemistry, Eleventh edition, Lippincott Williams and wilkins, P: 548-89 4.F.S.K.BARAR, Essentials of Pharmacotherapeutics, Fourth edition,2006, S.chand and company LTD, P: 177-91.

PowerPoint Presentation:

29 November 2011 59 WEB REFERENCE: 1.http://www.learnmem.org/cgi/content/full/7/5/287 2.http://www.springerlink.com/content/2bawak8nhed8q57t 3. http://www.medchem.ku.edu/faculty/david.html

PowerPoint Presentation:

29 November 2011 4JUNE 2008 60 Thank You!

Loaded for Shradda Godke by DR ANTHONY MELVIN CRASTO Glenmark scientist helping millions with websites and help Thanks to authorstream :

Loaded for Shradda Godke by DR ANTHONY MELVIN CRASTO Glenmark scientist helping millions with websites and help Thanks to authorstream 29 November 2011 4JUNE 2008 61 https://sites.google.com/site/anthonycrastoorganicchemistry/sites---my-own-on-the-net

authorStream Live Help