Download Tertiary Structure

Non-repetitive structures:
Other than a helix and b sheets, which form major portion of
proteins structure, there are other non repetitive folds or
structures. They are referred as coil or loop conformations.
The straight runs of secondary structures are reversed by
loops or coil structure.
b-turns connect the ends of two adjacent segments of antiparallel b sheets.
This turn is 180o involving 4 amino acids.
Type I and type II b turns: differ by 180o flip of peptide unit
linking residue 2 and 3.
Type II always have glycine as the third residue
Protein Tertiary and Quaternary structure:
•Overall three dimensional arrangement of all the atoms in a protein
(including folding and spatial organization of different secondary
structure) is referred as tertiary structure.
•Many proteins contain more than one polypeptide chains and their
three dimensional structure is dependent on the subunit organization.
The spatial organization of different subunits in protein is reffered as
quaternary structure.
•Protein are classified in two types based on higher order structure;
Fibrius proteins: Polypeptide chains arranged in long
stands or sheets.
Globular proteins: Polypeptide chains folded into a
spherical or globular shape
Fibrous proteins:
a keratin, collagen and silk fibroin
•Structural function to provide strength and flexibility
•The fundamental structural unit is simple repeat of an element of
secondary structure
•Mostly water insoluble
Priciple of permanent waving of hair:
Chemical manipulation of keratin structure
Collagen:
Found in connective tissue, tendons, cortilage
Structure left handed helix with three AA residue per turn
Three separate polypeptide chains are supertwisted about each other
35% Gly, 11% Ala, 21% Pro or hydroxyproline
Food product Gelatin (denatured collagen) is derived from collagen.
Closely packed because of Gly and sharp twisting by proline residue
Intr and inter-molecular crosslinking through Lys and His
Fibroin: A b pleated sheet
Insects, silkworm, spiders produce fibroin to fabricate cocoon,
web, nests.
Rich in Gly and Ala residues, permiting close packing with
interlocking side chain of AA residues.
The overall structure is stabilised by extensive hydrogen bonding
Silk does not stretch much because the b sheets are already in
extended form. The structure is flexible because of week
interaction between the sheets.
Globular proteins: Enzymes and regulatory proteins
Different segments of polypeptide chains fold back on each other
Resulting in a compact form.
Comparison of compact globular structure of BSA with its
extended forms ( helics and sheets)
Tertiary structure of Myoglobin