A-helix

Alpha-helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier (hydrogen bonding). This structure is also characterized by its pitch (the distance the helix rises along its axis per turn), which is 5.4 Å in the α-helix, with a diameter of about 12 Å. The α-helix is an essential part of the protein structure that contributes to the protein's stability and functionality.

Structure and Stability

The α-helix is stabilized by hydrogen bonds between the N-H group of one amino acid and the C=O group of another. These hydrogen bonds are formed in a regular pattern, giving the helix its characteristic shape and stability. The side chains of the amino acids in an α-helix project outward from the helix, allowing for interactions with other elements of the protein or the surrounding environment.

Function

The α-helix plays a critical role in the structure and function of many proteins. It can act as a structural framework, participate in the formation of protein channels, and contribute to the active sites of enzymes. Its ability to form coiled-coil structures, where two or more α-helices wrap around each other, is important in the dimerization or oligomerization of proteins, affecting their function and regulation.

Examples

Examples of proteins that contain α-helices include hemoglobin, which uses α-helices in its oxygen-binding sites, and keratin, a structural protein in hair, nails, and skin that consists of coiled-coil α-helices.

Discovery

The α-helix was first proposed by Linus Pauling and Robert Corey in 1951, based on X-ray diffraction patterns of proteins and the known chemistry of amino acids. This discovery was a significant milestone in the field of molecular biology, contributing to the understanding of protein structure and function.

See Also

• Protein structure
• Beta sheet
• Secondary structure
• Tertiary structure
• Quaternary structure