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Title: How protein structure affects function
Description: Various protein functions are determined by the structure of the proteins. These notes give an in depth understanding of the correlation between structure and function of proteins.
Description: Various protein functions are determined by the structure of the proteins. These notes give an in depth understanding of the correlation between structure and function of proteins.
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HOW PROTEIN
STRUCTURE IS RELATED
TO FUNCTION
C
...
Typical examples are:
collagen
haemoglobin and myoglobin
• enzymes
HOW PROTEIN STRUCTURE IS RELATED TO FUNCTION
Cont……
Collagen
• is the main protein in connective tissues in animals and
mammals
...
• tough bundles of collagen called collagen fibers are a major
component of the extracellular matrix that supports most
tissues and gives mostly the cells’ external structure
...
Structure of Collagen
• consists of three left-handed helical chains coiled
around each other
...
• Each helix has three amino acids per turn and is more
extended than an α-helix consisting mostly of the
repeating amino acids sequence –Gly-X-Y, where X is
usually proline and Y is usually hydroxyproline
...
Structure of Collagen cont…
...
• This hydroxylation is necessary for proper development
of collagen
...
• That is why people who suffer from scurvy due to lack
of vitamin C in their diet develop skin lesions, fragile
blood vessels (susceptible to bruising), loose teeth,
and bleeding gums because of poor development of
collagen
...
PRESENT ONLY IN MULTI-CELLULAR ORGANISMS
Similarities & Differences cont………
• Myoglobin has only one subunit and hemoglobin has four
subunits (2α and 2β subunits)
...
• Both have a heme prosthetic group which is made up of a
protoporphyrin ring and iron ion
...
• Iron atom can be in ferrous (+2) or ferric (+3) state and only +2
state binds oxygen
...
The molecules has one
polypeptide chain and its very compact with little space
inside
...
If oxygen bonds to heme only and not on the polypeptide
chain then what is the function of the polypeptide in
myoglobin and heme?
THREE MAIN REASONS:
1
...
2
...
Significantly decreases carbon monoxide affinity for
myoglobin (and hemoglobin)
EXPLANATION: Carbon monoxide binds to isolated heme with
much greater affinity than oxygen
...
An In-Depth Look At Haemoglobin
• Hemoglobin consists of 4 polypeptide chains, 2 of one
type, 2 of another (α2 and β2), held together by noncovalent bonds
...
• The three-dimensional structures of myoglobin and α and
β chains of hemoglobins are very similar
...
• In addition, the binding of oxygen to hemoglobin is
cooperative and is regulated by pH, CO2 and 2,3bisphosphoglycerate (BPG), which is not observed with
binding of oxygen to myoglobin
The Oxygen Dissociation Curve
• This is a graph that shows the percent saturation of
hemoglobin or myoglobin at various partial
pressures of oxygen
...
The Oxygen Dissociation Curve cont…
...
• The oxygen dissociation curve of myoglobin is
hyperbolic and that of hemoglobin is sigmoidal
implying that the binding of oxygen to hemoglobin
is cooperative
...
• Effects of pH on Oxygen Binding
Decrease in pH shifts oxygen dissociation curve to the right
because hemoglobin affinity for oxygen is decreased
...
The effect of pH and CO2 on oxygen binding
to hemoglobin actually promotes the release of oxygen from
oxyhemoglobin
...
• Effect of 2,3-bisphosphoglycerat (2,3 BPG)
Lowers oxygen affinity of hemoglobin by a factor of 26 which
results in hemoglobin unloading more of its oxygen at the tissue
level
...
Structural Basis Of Cooperativity And Regulation
• Why is the behaviour of hemoglobin with respect to
oxygen binding different from that of myoglobin?
• The allosteric properties of hemoglobin arise from
interactions between its subunits
...
The structures of oxyhemoglobin and
deoxyhemoglobin are very different:
**oxygenated hemoglobin is more compact and binding
of oxygen to hemoglobin results in a large structural
change at two of the four contact points between
subunits as one pair rotates relative to other pair of
protein chains**
Structural Basis Of Cooperativity And Regulation
cont…
...
• Binding of oxygen to the heme of one subunit
transmits signals that converts the T to the R form
in the other subunits of hemoglobin molecule
...
• When fully saturated, the hemoglobin molecules
releases one oxygen molecule which again results
into information being transmitted to other
subunits to snap from the R to T form which has
less affinity for oxygen
...
How BPG lowers oxygen affinity of hemoglobin
• Only one molecule of BPG is bound in the central
cavity of hemoglobin
...
How CO2 lowers oxygen affinity of hemoglobin
• Firstly, CO2 is transported as bicarbonate (HCO3-) in
red blood cells (RBCs):
CO2 + H20
HCO3- + H+
• Much of the H+ is taken up by deoxyhemoglobin in
the Bohr Effect
...
The remainder is that of CO2 bound to hemoglobin
as carbamate
...
Uptake of H+ helps buffer pH of
metabolically active cells
Differences between fetal and adult hemoglobin
• Foetal hemoglobin (Hb F) has four subunits (α2γ2)
just like adult hemoglobin A (α2β2)
...
• The γ chains of foetal hemoglobin at one position
have serine whereas in adults at this position there
is histidine
...
This enables the foetus to extract oxygen
from maternal circulation
Title: How protein structure affects function
Description: Various protein functions are determined by the structure of the proteins. These notes give an in depth understanding of the correlation between structure and function of proteins.
Description: Various protein functions are determined by the structure of the proteins. These notes give an in depth understanding of the correlation between structure and function of proteins.