Ch07-Structure-Function Relationships in Proteins.pdf

7 Structure–Function Relationships
in Proteins
Diseases can be caused by A multitude of different proteins can be formed from only mon amino acids
changes in protein structure that because these amino acids can be linked together in an enormous variety of
affect the protein’s ability to bind sequences determined by the ic code. The sequence of amino acids, its primary
other molecules and carry out its function. structure, determines the way a protein folds into a unique three-dimensional
They also can be caused by conformational structure, which is its native conformation. Once folded, the three-dimensional
changes in proteins that affect their solubil-
structure of a protein forms binding sites for other molecules, thereby dictating
ity and degradability. In amyloidosis AL,
immunoglobulin chains form an insoluble the function of the protein in the body. In addition to creating binding sites, a pro-
protein aggregate called amyloid ans tein must fold in such a way that it is flexible, stable, able to function in the cor-
and tissues. Alzheimer’s disease and familial rect site in the cell, and capable of being degraded by cellular enzymes.
amyloid polyneuropathy are neurodegener- Levels of protein structure. Protein structure is described in terms of four dif-
ative diseases characterized by the deposi- ferent levels: primary, secondary, tertiary, and quarternary (Fig. ). The pri-
tion of amyloid. Prion diseases result from mary structure of a protein is the linear sequence of amino acids in the polypep-
misfolding and aggregation of a normal cel- tide chain. Secondary structure consists of local regions of polypeptide chains
lular protein. Even in sickle cell anemia, the formed into structures generally stabilized by hydrogen bonds, such as the regular
mutation in hemoglobin principally affects structures called ␣-helices and ␤-sheets. The rigidity of the peptide backbone
the quarternary structure of hemoglobin and determines the types of