Protein structure

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Protein structure

Transcript of Protein structure

  • 1. Protein Structure and FunctionCompiled & Edited byDr. Syed IsmailVN Marathwada Agril. University Parbhani

2. DEFINITIONS OF PROTEINProteins are one of the essential building blocks of the human body.They provide amino acids, which are a nutritional requirement of the body to produce its own proteins and a variety of nitrogen-based molecules.It is common for programs to recommend a minimum of 50 grams of protein per day to maintain healthy levels.Proteins vary in structure as well as function. They are constructed from a set of 20 amino acids and have distinct three-dimensional shapes. 3. General Characteristics of ProteinsThey are the most complex and most diverse in chemical composition, conferring upon the different tissues.Protein molecule contains elements of C, H, O,N, S, and P together with traces of Fe, Cu, I, Mn, and Zn.It has a molecular weight of 5,000 to 3,000,000They are the most important of the biologic substances being the fundamental constituent of cell cytoplasm.They supply not only heat and energy but also material for building and repair.Unlike carbohydrates and lipids, only small amounts of protein is temporarily stored in the body, and which can be quickly used up upon demand. 4. FUNCTIONS OF PROTEIN 5. FUNCTIONS OF PROTEINAntibodies - are specialized proteins involved in defending the body from antigens (foreign invaders). One way antibodies destroy antigens is by immobilizing them so that they can be destroyed by white blood cells.Enzymes - are proteins that facilitate biochemical reactions. They are often referred to as catalysts because they speed up chemical reactions. Examples include the enzymes lactase and pepsin. Lactase breaks down the sugar lactose found in milk. Pepsin is a digestive enzyme that works in the stomach to break down proteins in food.Hormonal Proteins - are messenger proteins which help to coordinate certain bodily activities. Examples include insulin, Insulin regulates glucose metabolism by controlling the blood- sugar concentration. 6. FUNCTIONS OF PROTEINContractile Proteins - are responsible for movement. Examples include actin and myosin. These proteins are involved in muscle contraction and movement.Structural Proteins - are fibrous and stringy and provide support. Examples include keratin, collagen, and elastin. Keratins strengthen protective coverings such as hair, quills, feathers, horns, and beaks. Collagens and elastin provide support for connective tissues such as tendons and ligaments.Storage Proteins - store amino acids. Examples include ovalbumin and casein. Ovalbumin is found in egg whites and casein is a milk-based protein.Transport Proteins - are carrier proteins which move molecules from one place to another around the body. Examples include hemoglobin and cytochromes. Hemoglobin transports oxygen through the blood. Cytochromes operate in the electron transport chain as electron carrier proteins. 7. Classification of ProteinsBased on Composition:Simple proteins composed of entirely amino acids only.Ex. Albumin, GlobulinComplex or Conjugated proteins made up of amino acids and other organic compounds. The non- amino acid group is termed as the prosthetic group.Ex. Nucleoproteins, lipoproteins,glycoproteins, metalloproteins 8. Classification of ProteinsBased on Axial Ratio:Axial ratio is the ratio of the length to the breath.Globular proteins with axial ratio less than 10 but not below 3 or 4. They are compactly folded and coiled.Ex. Insulin, plasma albumin, globulin,enzymesFibrous proteins with axial ratio greater than 10. They are spiral and helical and are cross linked by disulfide and hydrogen bonds.Ex. Keratin, myosin, elastin, collagen 9. Globular ProteinsGlobular proteins have their axial ratio less than 10 but not below 3 or 4. They are compactly folded and coiled.Examples are insulin, plasma albumin, globulin, enzymes 10. Fibrous ProteinsFibrous proteins are spiral and helical and are cross linked by disulfide and hydrogen bondsExamples are keratin, myosin, elastin, collagen 11. Based on Biological FunctionsStructural proteins: collagen, elastin, keratin, fibroin of silk and websTransport proteins: hemoglobin, myoglobin, lipoproteinsProtective proteins: immunoglobulins, fibrinogen, thrombin, snake venoms, bacterial toxinsContractile proteins: actin, myosin, tubulinCatalytic proteins: enzymesRegulatory proteins: hormonesStorage proteins: ferritin, hemosiderin, gluten, casein, ovalbuminReception of Stimuli: rhodopsin, membrane receptor proteins, acethylcholine, insulinGermicidal proteins: Polymyxin B1, Gramicidin S 12. Shape = Amino Acid SequenceProteins are made of 20 amino acids linked by peptide bondsPolypeptide backbone is the repeating sequence of the N-C-C-N-C-C in the peptide bondThe side chain or R group is not part of the backbone or the peptide bond 13. Composed of a chain of amino acids.R|H2N--C--COOH|HProteins20 possible groups 14. 0HCOOCNHCOCNHCOOCNHCOOCNH2333 - -- 15. Polar Basic Acid ? AcidAmineDifferent Amino Acid ClassesOH O H H2N C CRGenericNon-polar C C C OH HH OH+N H H2N C NH CC HistidineHH2N C C H HO OHOC OH C Aspartic acid CC COHH H O HS HH2NCysteineOHH H O H HH2N CC C Alanine 16. Non-Polar Amino Acids OH OHH2NCC H Glycine Leucine OHO HH2N C C H3C CH3 HC HHC Methionine OH O HH2N CC H3C H H C HHCS Alanine OH H H OH HH2N C C C Valine OHO HH2N C C H3C CH3 HC PhenylalanineOHH H O H H2NCCC Tryptophan OH O H H2NCCNHH C H Isoleucine OHO HH2N C C H3C H HC HH3CC Proline OH O HH2N+ CC H2C CH2 H2C Protein Structure 17. Polar Amino AcidsCysteine CC C OH H H OHS HH2N Serine OH O H H2NCCHO CH3 H C Threonine OHO HH2N C C H H COHHC H Tyrosine HO H HO HH2N C C C OH AsparagineHH2NC C H H O OHOCNH2C Glutamine H H2N CC HHO OH O C NH2CCHH 18. Acidic Amino Acids Aspartic acid H H2NC CHH O OH O COHCGlutamicacid H H2N C C HHOOH O C OH C CHH 19. Basic Amino Acids Histidine C C C OHHHOH+N H H2N C NHCCLysine OH O H H2N CC +H3NHH C H H CC HH H H C Arginine OHO HH2N C C H H CHHC C H H H N+H2NNH2C Protein Structure 20. Levels of Protein OrganizationPrimary Structure - The sequence of amino acids in the polypeptide chainSecondary Structure - The formation of helices and b pleated sheets due to hydrogen bonding between the peptide backboneTertiary Structure - Folding of helices and sheets influenced by R group bondingQuaternary Structure - The association of more than one polypeptide into a protein complex influenced by R group bonding 21. Levels of Protein Organization Primary Structure Met-Gly-Ala-Pro-His-Ile-Asp-Glu-Met-Ser-Thr-...The sequence of amino acids in the primary structure determines the folding of the molecule. Protein Structure 22. Protein Secondary StructureThe peptide backbone has areas of positive charge and negative chargeThese areas can interact with one another to form hydrogen bondsThe result of these hydrogen bonds are two types of structures: helicesb pleated sheets 23. + - Protein Secondary Structure: Helix CO OHC N H H H CHOHCH O C N HH HCH H C H NCOC H N O C COCHN C H N COCO C O C O CHNHN C H N 24. +-Protein Secondary Structure: HelixC O OH C N HH HCHO H C H OC NH H H C H HCHN C O C H NOCCO C H N CHNC O C O C OCOCH N H N CHN 25. Protein Secondary Structure: HelixR R R R RR RRR R R R RR R groups stick out from the helix influencing higher levels of protein organization 26. Yeast Cytochrome C Oxidase Subunit IV LeaderMLSLRQSIRFFKPATRTLCSSRYLL R Y P LTCSR L S T IKPRF A F M RQLLS SThis would localise specific classes of amino acids in specific parts of the helix The order of the amino acids determines the hydrogen bonding Neutral Non-polar Polar Basic Acidic 27. Protein Secondary Structure: b Pleated Sheet NH C O C H CCNO N H C O CHCCN O N H CO CHC C N O NH CO C H C C NO NH C O C H CCNO N H C O CHCCN O N H CO CHC C N O NH CO C H C C NO 28. Protein Secondary Structure: b Pleated SheetNH C O C HCCN O N H C OCHCC N O N HC OCH C C N ONHC O C H C CN ONH C O C HCCN O N H C OCHCC N O N HC OCH C C N ONHC O C H C CN ONH C O C HCCN O N H C OCHCC N O N HC OCH C C N ONHC O C H C CN O 29. Levels of Protein Organization Tertiary StructureTertiary structure results from the folding of helices and b pleated sheetsFactors influencing tertiary structure include:Hydrophobic interactionsHydrogen bondingDisulphide bridgesIonic bonds 30. Hydrophobic interactions Valine OH OHH2NCC H3C CH3 H CProline OHO H H2N+ C C H2CCH2 H2COH O H H2N C CHGlycine 31. Hydrogen Bonding Asparagine H H2N C CHHO OH O C NH2 CGlutamine HH2N C C H H OOH OCNH2 C C H HN-------H (+) (-) O -------Cslightly slightly 32. Disulphide bridgesCysteine C C C OH HH OHS H H2N Cysteine C CC OHHH O HS H H2NCysteine CC C OH H H OS HH2N Cysteine C C C OHHHOS H H2N 33. Ionic Bonds Glutamic acidHH2NC C H H O OHOCO-C C H H ArginineOH OHH2N C C H HC HHC C H H HN +H2NNH2C 34. e.g.G-3-P Dehydrogenase Tertiary Structure 35. Levels of Protein Organization Quaternary StructureQuaternary structure results from the interaction of independent polypeptide chainsFactors influencing quaternary structure include:Hydrophobic interactionsHydrogen bondingThe shape and charge distribution on amino acids of associating polypeptides 36. G-3-P Dehydrogenase from Bacillus stearothermophilus 37. Protein structure 38. Globular and Fibrouse.g. haemoglobin3 structure normally folds up in a ballhydrophilic R groups point outwardsHydrophobic R groups point inwardssolublemetabolic functionse.g. collagen2 structure does not fold up, form fibresnot surrounded by hydrophilic R groupsinsolublestructural functions 39. HaemoglobinHaemoglobin is a globular protein with a prosthetic iron groupIn adults, hemoglobin is made up of 4 polypeptides (2 polypeptide chains and 2 b polypeptide chains)Each polypeptide surrounds a prosthetic haem groupHydrophobic interactions between side groups pointing inwards maintain the structureHydrophilic s