Α helix

α Helix is a common secondary structure of proteins and is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid located three or four residues earlier along the protein sequence.

The α helix is one of the principal structural motifs in proteins, with about 10-20% of all residues in most proteins being incorporated into α helices. The α helix was first discovered by Linus Pauling, Robert Corey, and Herman Branson in 1951.

Structure

The α helix has 3.6 amino acids per turn. It is tightly packed, with only a small hollow tube running up the middle of the helix. This is too small to allow the passage of other molecules such as water.

Each amino acid in the helix contributes one hydrogen bond, which is a strong interaction in the relatively dry environment inside a protein. This bonding helps to stabilize the helical structure.

Properties

The α helix has several important properties. It is rigid and its shape is maintained by hydrogen bonds. It is also amphipathic, with one side being hydrophilic (or water-loving) and the other side being hydrophobic (or water-fearing). This property is important in the folding of proteins and their interactions with other molecules.

Role in Proteins

In proteins, α helices are major structural components and can be found in almost every globular protein. They also occur in fibrous proteins such as keratin and collagen. The α helix is a key player in the formation of the protein's overall three-dimensional structure.

See Also

• Beta sheet
• Protein structure
• Protein folding