3. Major structural and functional aspects of the body
Our 3/4th dry body weight are made of proteins
Major components - Carbon, Hydrogen, Oxygen and Nitrogen
All proteins are polymers of amino acids.
“proteios” - primary or first
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INTRODUCTION
7. POLYPEPTIDES
Polypeptide chains - Chains having less than 40-50 amino acids.
Larger than this size, they are called proteins.
Proteins - long polypeptide chains.
The structure, function and general properties of a protein are all
determined by the sequence of amino acids.
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9. PRIMARY STRUCTURE
Sequence of amino acids
Example: Gly - Ala - Val (1)
Gly - Val - Ala (2)
Largely responsible for protein function
Change in protein sequence –Affects
protein’s overall structure &function.
Example – Sickle cell anaemia
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10. A chain - 21 amino acids
B chain - 30 amino acids
Interchain disulfide bonds – 7Cys A & 7Cys B, 20Cys A & 19Cys B
BRANCHED PROTEINS – HUMAN INSULIN
7
7
20
6 11
19
21 amino acids
30 amino acids
10
Ile
Thr
11. CIRCULAR PROTEINS - PROINSULIN
Proinsulin is a single polypeptide chain with 86 amino acids
Removal of C peptide
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12. Even a single amino acid change (mutation) in the linear sequence
may have profound biological effects
Example: Sickle cell anaemia (change in 2 amino acids out of 600).
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ROLE OF PRIMARY STRUCTURE IN BIOLOGICALACTIVITY
13. SECONDARY STRUCTURE
Primary sequence or main chain of the protein must
organize itself to form a compact structure
Polypeptide chain by twisting or folding is referred to as
secondary structure.
Two types of secondary structure
α - Helix β – Pleated
sheets
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14. Spiral structure of protein
Tightly packed coiled structure
Stabilized by extensive hydrogen bonding
Each turn of α -helix contains 3.6 amino acids
The spacing of each amino acid is 0.15 nm
The right handed α-helix is more stable than left handed helix
Proline – Helix breaker (not compatible with helix)
α - HELIX
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15. Two or more segments of fully extended peptide chains
Sheet-like structure held together by hydrogen bonds
The distance between adjacent amino acids is 3.5Å
Two types-
β – PLEATED SHEETS
• Parallel sheets
• Anti parallel sheets
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16. PARALLEL & ANTI PARALLEL BETA SHEETS
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OTHER ELEMENTS
β – Turns
18. TERTIARY STRUCUTURE
Three-dimensional arrangement of protein structure
Secondary structure elements come together to form the tertiary structure
Stability of structure
• Hydrogen bonds
• Ionic bonds
• Dipole-dipole interactions
• Hydrophobic interactions
• Disulfide bonds (safety pins)
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19. MYOGLOBIN
It has 154 amino acids residues
Myoglobin contains a heme (prosthetic) group
Oxygen bound myoglobin is called oxymyoglobin
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20. • Pairs of cysteines can form disulfide bonds
between different parts of the main chain
• This adds stability and is common in
extracellular proteins
DISULFIDE BONDS
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21. HYDROGEN BONDING
Hydrogen bonding is a special
type of dipole-dipole
attraction between molecules,
not a covalent bond to a
hydrogen atom.
Ionic bonding is the
complete transfer of
valence electron(s) between
atoms
IONIC BONDING
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22. Not attractive interactions, but results
from inability of water to form
hydrogen bonds with side chains.
Intermolecular forces that occurs
between atoms and non polar molecules
as a result of motion of electrons.
HYDROPHOBIC INTERACTIONS VAN DER WAALS INTERACTIONS
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23. QUATERNARY STRUCTURE
Polypeptides aggregates together to form one functional protein
Each polypeptide chain is called as subunit or monomers
Structure may be monomer, dimer, trimer, tetramer and so on
Hydrogen bonds
Electrostatic bonds
Hydrophobic bonds
Van der waals forces
SOURCES STABILIZING STRUCUTRE
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24. Two identical α and β chains
Subunit is linked covalently to molecule of heme
Held together by
Hydrophobic interactions
Hydrogen bonding
Salt bridges
HAEMOGLOBIN
α chain - 141 amino acids
β chain - 146 amino acids
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26. ROLE OF PROTEIN STRUCTURE IN DRUG DESIGN
Structure based drug design:
Ligand based drug design
Receptor based drug design
Computer aided drug design:
Docking
Denovo Drug design
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Protein structure – Core of drug design
27. STRUCTURE BASED DRUG DESIGN
Knowledge of 3D structure of biological target
Obtained by protein prediction
Ligand based design Receptor based design
• Finding ligand for receptor
• Large number of potential Ligand
screening
• Building ligands according to receptor
• Ligands are built by small pieces in a
stepwise manner
• This pieces may be Individual Atoms
or Molecular fragments
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29. COMPUTER AIDED DRUG DESIGN
Docking
Ability to position a ligand in a active site or
a designated site of protein
Calculating the specific binding affinities
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Denovo Drug design
Iterative process using 3D structure of
target to find new medications
30. CONCLUSION
Protein structure plays a key role in biochemistry studies
It plays a key role in drug design
Without protein structure drug design cannot be done
The primary use of protein structure for the development of drug
compounds is to determine the structure of a protein in complex with
a tool compound
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31. BIBLIOGRAPHY
Andreeva A. Lessons from making the Structural Classification of Proteins (SCOP)
and their implications for protein structure modelling: Biochem Soc Trans.
2016: 15(43): 937-45.
Chothia C. Hubard T. Brenner S. Barns. Murzin A. Protein Folds in the α and β
classes: Annu. Rev. Biophys. Biomol. Struct. 1997: 26; 597-627.
Satyanarayana U. Chakrapani U. Biochemistry. Proteins and amino acids: 4th ed. New
Delhi; Reed Elsevier India private Limited; 2013.
Staker BL. Buchko GW. Myler PJ. Recent contributions of Structure-Based Drug
Design to the development of antibacterial compounds: Curr Opin Microbiol.
2015: 27; 133-8.
Vasudevan DM. Sreekumari S. Vaidyanathan K. Textbook of biochemistry for medical
students: Proteins: Structure and Function. 8thed. New Delhi; Jaypee brothers
publications (P) Ltd.; 2017.
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