structure of proteins posttraslational modification of proteins and its significance primary structure secondary structure tertiary structure quartinary structure denaturation renaturation

1. Assembly of spatial structure of
proteins.
Posttranslational modification of
proteins and its significance
Tural Abdullayev
Group 30

2. Assembly of spatial structure of
proteins
• 4 orders of protein structure:
1. Primary structure
− The amino acids in a polypeptide chain
2. Secondary structure
− The folding of short ( 3 – 10 residues) contiguous segments of
polypeptide into geometrically ordered units
3. Tertiary structure
− Three – dimensional assembly of secondary structural units to
form larger functional units
4. Quaternary structure
− Association of individual polypeptide chain subunits in a
geometrically specific manner

3. Assembly of spatial structure of
proteins
• Primary structure
– Unique sequence of amino acid
– Peptide bonds between Amino Acids
– Sequence determined by DNA
– Chang in primary structure can affect
a protein’s conformation and ability
to function

4. Assembly of spatial structure of
proteins
• Secondary structure:
– Has hydrogen bonds
– Has 2 structures
1. α – helix
− It has a rigid, stable conformation that maximizes
hydrogen bonds between each carbonyl oxygen atom
and amid hydrogen (N – H) of amino acid residue
located down the chain
− Trans side chains of amino acids project outward from
the helix
2. β – sheets
− The hydrogen bonding usually occurs between regions
of neighboring polypeptide strands aligned parallel to
each other
− Carbonyl oxygen of one peptide bonded is hydrogen
– bonded to the nitrogen
− Optimal hydrogen binding occurs when the sheet is
bent to form β – pleated sheets

5. • Tertiary structure:
– Types of interaction:
1. Hydrogen bonds
2. Ionic bonds
3. Hydrophobic interactions
– Usually inside the protein
4. Covalent bonds
– Disulfide bridge formed between
the Sulfhydryl groups (SH) of
cysteine amino acids
Assembly of spatial structure of
proteins

6. Assembly of spatial structure of
proteins
• Quarternary structure
– Aggregation of two or more polypeptide
subunits
– Forms 2 types of proteins:
1. Globular
2. Fibrous
– Not found in all proteins
– Water soluble
– Compact ,spherical
 The biological function of some
molecules is determined by multiple polypept
ide chains – multimeric proteins.
 Subunits are held together by non covalent
interactions.
 Eg: Hemoglobin has the subunit composition
a2b2

7. Denaturation
• A change in a shape of the protein that
disturbs its function
• Alterations in the environment disrupt bonds
and forces of attraction
– pH
– Salt concentration
– Temperature

8. Posttranslational modification of
proteins and its significance
• After the proteins emerge from the ribosome, they
undergo posttranslational modification
• Modifications may occur on:
1. Amino acid side chains
2. Protein’s C – terminal
3. Protein’s n – terminal

9. • Initial Methionine
– is removed by specific proteases
– Initial Methionine is not the N – terminal of all mature proteins
• Amino acid residues within the peptide chain can be
modified enzymatically to alter the activity or stability of
the proteins:
– Direct it to a subcellular compartment, or prepare it for secretion
from the cell
• Amino acid residues are modified enzymatically by the
addition of various types of functional groups
– For example: N – terminal amino acid is acetylated, and methyl
groups can be added to lysine residues
Posttranslational modification of
proteins and its significance

10. Posttranslational modification of
proteins and its significance
• Proline and lysine residues can be modified by
Hydroxylation
– In collagen, hydroxylation lead to stabilization of the
protein
• Carboxylations
– important for the function of proteins involved in blood
coagulation
• Formation of γ – carboxylglutamate allows these proteins to
chelate Ca2+ , a step in Clot Formation
• ADP – ribose group
– Can be transferred from NAD + to certain proteins

11. • Addition and Removal of Phosphate groups
– Serve to regulate the activity of many proteins
• Glycosylation
– Addition of – CH groups
– Is a common modification
– Mainly occurs on proteins that are going to be secreted or
incorporated into lysosomes or cellular membranes
– Also can promote the protein folding and improve stability
Posttranslational modification of
proteins and its significance