Protein Secondary Structure HOME PAGE
A. DETERMINATION OF PROTEIN STRUCTURE IN 3-D: X-RAY CRYSTALLOGRAPHY
B. OVERALL CONFORMATION OF PROTEINS
Proteins have a covalently bonded backbone as discussed in Lecture 5 in relation to amino acid sequence determination. But the 3-D shape or conformation is held together by weaker bonding of the non-covalent type. The linear form of the polypeptide backbone of the protein folds into a tightly held shape which is chemically stabilized by weak bonds like hydrogen bonds, ionic bonds and hydrophobic interactions among non-polar amino acid side chains.
To reduce the complexity of protein structure to a manageable level for our study and understanding, the protein is considered to have 4 levels of structure.
Four Levels of Protein Structure:
1. Primary Structure- Polypeptide backbone
2. Secondary Structure- Local Hydrogen bonds along the backbone
3. Tertiary structure- Long distance bonding involving the AA side chains
4. Quaternary structure- Protein-Protein interactions leading to formation of dimers, tetramers, etc.
C. PRIMARY STRUCTURE OF PROTEINS
D. SECONDARY STRUCTURE OF PROTEINS
In 1950's, Linus Pauling named the first structures he found by X-ray diffraction, the Alpha Helix and the second structure he found was called Beta Sheet. We continue to use these names today for two forms of secondary structure and add a third type forms in regions where the protein bends back on itself to form its compact shape or conformation.
The 3 Types of Protein Secondary Structure:
Alpha-helix
Beta-sheet
Turns or Bends (Bends in backbone to fold the polypeptide back on itself)
E. LOCAL HYDROGEN BONDING FORMS SECONDARY STRUCTURE
H. TURNS AND BENDS IN THE POLYPEPTIDE BACKBONE
©Wilbur H. Campbell, 1995; wcampbel@mtu.edu