Michael Pikaart/Biochem StructureIntro

Chem311 Course Page 1 Introduction to protein structure

IntroductionIntroduction

A protein's function depends on the proper folding of the linear polymeric chain of amino acids making up its polypeptide sequence. Folding of a polypeptide occurs by way of rotation of the single bonds in either side of each amino acid residue's alpha carbon, characterized by the Φ and Ψ angles. In folded proteins, stretches of amino acids typically have a re-iterated and restricted set of Φ and Ψ angles, giving rise to a length of stable secondary structure. If this structure has a rotational displacement, the result is a helical secondary structure; if the structure occurs in a zig-zag arrangement, a sheet secondary structure results. Here we will explore these two types of secondary structures, as found in actual proteins.

Alpha helixAlpha helix

Helix or screw structures are found in lots of contexts, both in nature and in man-made objects like these:

Helices have a twist to them, either right handed or left handed. A normal right-tighty screw is a right-handed helix. We take a look at a protein called GCN4, a transcription factor found in yeast that binds DNA and regulates expression of genes responsible for synthesis of amino acids. (For more information, go to [1])