Protein Function
Hemoglobin
Functions of Globular Proteins
• Storage of ions and molecules
– myoglobin, ferritin
• Transport of ions and molecules
– hemoglobin, serotonin transporter
• Defense against pathogens
– antibodies, cytokines
• Muscle contraction
– actin, myosin
• Biological catalysis
– chymotrypsin, lysozyme
Interaction with Other Molecules
• Reversible, transient process of chemical equilibrium:
A + B ↔ AB
• A molecule that binds is called a ligand (typically a small
molecule)
• A region in the protein where the ligand binds is called
the binding site
• Ligand binds via non-covalent forces, which enables the
interactions to be transient
Specificity: Lock-and-Key Model
• Proteins typically have high specificity: only certain ligands bind
• High specificity can be explained by the complementary of the
binding site and the ligand.
• Complementary in
– size,
– shape,
– charge,
– or hydrophobic/hydrophilic character
, Specificity: Induced Fit
• Conformational changes may occur upon ligand binding
(Daniel Koshland in 1958)
– This adaptation is called the induced fit
– Induced fit allows for tighter binding of the ligand
– Induced fit allows for high affinity for different ligands
• Both the ligand and the protein can change their conformations
Globins are oxygen-binding proteins
• Oxygen is poorly soluble in aqueous solutions and cannot be carried to
tissues in sufficient quantity if it is simply dissolved in blood
• Biological problems:
• Protein side chains lack affinity for O2
• Some transition metals bind O2well but would generate free radicals if
free in solution
• Organometallic compounds such as heme are more suitable, but Fe2+
in free heme could be oxidized to Fe3+
• Biological solution
– Capture the oxygen molecule with heme that is protein bound
Myoglobin (storage) and hemoglobin (transport) can bind oxygen via a
protein-bound heme.
Hemoglobin
Functions of Globular Proteins
• Storage of ions and molecules
– myoglobin, ferritin
• Transport of ions and molecules
– hemoglobin, serotonin transporter
• Defense against pathogens
– antibodies, cytokines
• Muscle contraction
– actin, myosin
• Biological catalysis
– chymotrypsin, lysozyme
Interaction with Other Molecules
• Reversible, transient process of chemical equilibrium:
A + B ↔ AB
• A molecule that binds is called a ligand (typically a small
molecule)
• A region in the protein where the ligand binds is called
the binding site
• Ligand binds via non-covalent forces, which enables the
interactions to be transient
Specificity: Lock-and-Key Model
• Proteins typically have high specificity: only certain ligands bind
• High specificity can be explained by the complementary of the
binding site and the ligand.
• Complementary in
– size,
– shape,
– charge,
– or hydrophobic/hydrophilic character
, Specificity: Induced Fit
• Conformational changes may occur upon ligand binding
(Daniel Koshland in 1958)
– This adaptation is called the induced fit
– Induced fit allows for tighter binding of the ligand
– Induced fit allows for high affinity for different ligands
• Both the ligand and the protein can change their conformations
Globins are oxygen-binding proteins
• Oxygen is poorly soluble in aqueous solutions and cannot be carried to
tissues in sufficient quantity if it is simply dissolved in blood
• Biological problems:
• Protein side chains lack affinity for O2
• Some transition metals bind O2well but would generate free radicals if
free in solution
• Organometallic compounds such as heme are more suitable, but Fe2+
in free heme could be oxidized to Fe3+
• Biological solution
– Capture the oxygen molecule with heme that is protein bound
Myoglobin (storage) and hemoglobin (transport) can bind oxygen via a
protein-bound heme.
