(a) a helix
Pauling and Corey propose this in 1951, which is regarded as one milestone in the
biochemistry research. In this structure, the poly P E
pt chains fold around the long
axis in such a way that the -NH group of each A m
a bind to the –CO group of the
fourth residue by a hydrogen bond, throughout the chain These hydrogen bonds are
parallel to the long axis with the side chains protruding outward in a manner that
each turn of a helix comprises 3.6 A m
a residues. Each A m
a residue is present at a
distance of 0.15 nm from one another along the axis. Example of a helical p
R
t
structure is hair p
R
t i.e., Keratin (Ikai 1980).
(b) b sheet
The b sheet also known as b -Pleated sheet is a common motif of regular secondary
structure of p
R
t . Beta sheet consists of beta strands connected laterally by at least
two or three backbone hydrogen bonds forming a twisted, pleated sheet. A beta
strand is a stretch of poly P E
pt chain typically 3–10 A m
a long with backbone in an
extended conformation. They have implicated the supramolecular association of
beta sheets in formation of the p
R
t aggregates and fibrils observed in many H
u
M
diseases (D
I
se ), notably the amyloidosis such as Alzheimer’s D
I
se ′.
Tertiary Structure
Tertiary structure represents the folding of p
R
t that also controls the basic functioning of p
R
t . Stabilization of tertiary structure is achieved by non-local interactions, through salt bridges, hydrogen bonds, di sulphide bonds and
post-translational modifications. Tertiary structure involves three-dimensional
folding of the chain; stabilized by the bonding between the distant parts of the
sequence. The long poly P E
pt chains are tightly folded in to a compact form because
of the following interactions of -R groups of side chains of A m
a .
Hydrogen Bonding
Along with the hydrogen bonding between P E
pt bonds that give rise to the secondary structure of p
R
t , the hydrogen linkage may also be present between the A m
a
side chains.
Disulphide Bonding
The disulphide bonds cross-link with the poly P E
pt chain. The p
R
t folds to bring two
cysteine residues together thus the two -SH side chains oxidize and form a covalent
disulphide (S–S) linkage (Mc Ardle et al. 2001).
23 Protein and Enzymes Isolated from Plant Sources …
801
Pauling and Corey propose this in 1951, which is regarded as one milestone in the
biochemistry research. In this structure, the poly P E
pt chains fold around the long
axis in such a way that the -NH group of each A m
a bind to the –CO group of the
fourth residue by a hydrogen bond, throughout the chain These hydrogen bonds are
parallel to the long axis with the side chains protruding outward in a manner that
each turn of a helix comprises 3.6 A m
a residues. Each A m
a residue is present at a
distance of 0.15 nm from one another along the axis. Example of a helical p
R
t
structure is hair p
R
t i.e., Keratin (Ikai 1980).
(b) b sheet
The b sheet also known as b -Pleated sheet is a common motif of regular secondary
structure of p
R
t . Beta sheet consists of beta strands connected laterally by at least
two or three backbone hydrogen bonds forming a twisted, pleated sheet. A beta
strand is a stretch of poly P E
pt chain typically 3–10 A m
a long with backbone in an
extended conformation. They have implicated the supramolecular association of
beta sheets in formation of the p
R
t aggregates and fibrils observed in many H
u
M
diseases (D
I
se ), notably the amyloidosis such as Alzheimer’s D
I
se ′.
Tertiary Structure
Tertiary structure represents the folding of p
R
t that also controls the basic functioning of p
R
t . Stabilization of tertiary structure is achieved by non-local interactions, through salt bridges, hydrogen bonds, di sulphide bonds and
post-translational modifications. Tertiary structure involves three-dimensional
folding of the chain; stabilized by the bonding between the distant parts of the
sequence. The long poly P E
pt chains are tightly folded in to a compact form because
of the following interactions of -R groups of side chains of A m
a .
Hydrogen Bonding
Along with the hydrogen bonding between P E
pt bonds that give rise to the secondary structure of p
R
t , the hydrogen linkage may also be present between the A m
a
side chains.
Disulphide Bonding
The disulphide bonds cross-link with the poly P E
pt chain. The p
R
t folds to bring two
cysteine residues together thus the two -SH side chains oxidize and form a covalent
disulphide (S–S) linkage (Mc Ardle et al. 2001).
23 Protein and Enzymes Isolated from Plant Sources …
801