Protein Shape and Function

A protein’s shape is critical to its role in the cell. How does a chain of amino acids influence the shape of a protein? Unlike the loose links in a metal or plastic chain, amino acids join together at certain angles, forming regular patterns. Some of these patterns resemble coils like those of a telephone cord or folds like those of a pleated cloth. These patterns are then “folded,” or shaped, to form a more complex three-dimensional structure. The shape of a protein is anything but haphazard. Indeed, a protein’s form is critical to its function, which becomes all too evident when a flaw occurs in the amino acid chain.

One Theory on the Mechanism of Disease

In recent years scientists have focused their attention on a disease that some attribute to an abnormal form of a protein called a prion. The theory is that disease results when defective prions bind to normal prion proteins, causing the normal protein to misfold. The result is “a chain reaction that propagates the disease and generates new infectious material,” says the journal Scientific American.

What may have been an instance of prion-based disease first came to public attention in the 1950’s in Papua New Guinea. Certain isolated tribes engaged in a form of cannibalism for religious reasons, and this led to a disease called kuru, with symptoms similar to those of Creutzfeldt-Jakob disease. Once the afflicted tribes gave up this religious ritual, the incidence of kuru rapidly declined, and it is now virtually unknown.

Amazing Design!

Happily, though, proteins are usually folded correctly and go about their tasks with amazing cooperation, efficiency, and fidelity. This is remarkable considering that there are over 100,000 different kinds of proteins in the human body, all complex chains arranged into thousands of types of folds.

[Diagram/Pictures on page 26]

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How does a protein “fold”?

Single amino acids are linked together to . . .

1 form a chain, then . . .

2 they form patterns, such as coils or pleats, then . . .

Coils

Pleats

3 fold into a more complex three-dimensional structure, which may be . . .

4 just one subunit of a complex protein