BIOCH 200 Unit 4 - Protein Function (Terms)

Myoglobin

A monomer cytosolic protein found in muscles that folds into one domain, functioning to transport and store O2 within tissue

Hemoglobin

A heterotetramer cytosolic protein found in red blood cells comprised of 4 subunits each with one domain, functioning to transport O2 from lungs to tissues

Red Blood Cells

Cells that travel in the blood responsible for binding to O2 in the lungs and transporting it to be released in the tissues

Ligand

Small molecules that reversibly bind to proteins through noncovalent interactions

K_d

The midpoint of a ligand binding curve which represents a concentration of half binded half not binded ligand and protein

Heme

An ampipathic prosthetic group found on proteins that require binding or carrying of oxygen

HisF8

The proximal histidine residue in myoglobin that is closer to the Fe²⁺ ion, found as the 8th residue on the F helix of the protein that is responsible for holding the porphyrin ring of heme in place to myoglobin

HisE7

The distal histidine residue in myoglobin that is farther from the Fe²⁺ ion, found as the 7th residue on the E helix of the protein that is responsible for assisting O2 binding to heme’s 6 coordinate location through H-bond stabilization

Apoprotein

A protein that requires a prosthetic group to carry out its function that is missing its prosthetic group

Holoprotein

A protein that requires a prosthetic group to carry out its function that is carrying its prosthetic group

Globin

The apoprotein of myoglobin, missing the heme prosthetic group

Conservative Substitution

An amino acid substitution that has minor effects on the overall protein’s structure and function

Critical Substitution

An amino acid substitution that changes the overall protein’s structure and may change function depending on its location

Cooperative Binding Affinity

A binding relationship in which the ligand affinity to a protein will change as more ligand binds to the protein

Tense (T) State Hemoglobin

The low affinity conformation of hemoglobin with a large central cavity, present in the deoxy form of hemoglobin when O2 binding is low

Relaxed (R) State Hemoglobin

The high affinity conformation of hemoglobin with a small central cavity, present in the oxy form of hemoglobin when O2 binding is high

Allostery

A relationship in which the binding of a ligand at one site of a protein affects the binding of ligands at other sites on the same protein

Effectors

Compounds which, upon binding, alter affinity at other binding sites

Homoallostery

A relationship in which the binding of an effector affects further binding of the same compound, typically as ligands increasing their own affinity to a protein

Heteroallostery

A relationship in which the binding of an effector affects further binding of a different compound

Activator

An effector that increases the binding affinity of a ligand in a heteroallosteric relationship

Inhibitor

An effector that decreases the binding affinity of a ligand in a heteroallosteric relationship

Allosteric Inhibition

The use of an inhibitor to alter an active site so that it decreases binding affinity to a different substrate

Allosteric Activation

The use of an activator to alter an active site so that it increases binding affinity to a different substrate

Positive Cooperativity

A cooperative binding relationship in which the ligand affinity to a protein will increase as more ligand binds to the protein

2,3-bisphosphoglycerate (BPG)

A negative heteroallosteric inhibitor for oxygen binding to hemoglobin that is essential in the stabilization of the T state in hemoglobin