Helical wheel

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Helical wheel

A helical wheel is a graphical representation used in biochemistry and molecular biology to illustrate the properties of alpha helices in proteins. This method helps in visualizing the distribution of amino acids along the helical structure, providing insights into the amphipathic nature of the helix.

Structure and Representation

The helical wheel projection maps the amino acids of an alpha helix onto a two-dimensional plane. Each amino acid is represented as a point on a circle, with the sequence progressing around the circle in a helical manner. Typically, the circle is divided into 18 or 20 segments, corresponding to the number of residues per turn of the helix.

Applications

Helical wheel diagrams are particularly useful for identifying the amphipathic nature of alpha helices. Amphipathic helices have one side that is hydrophilic (water-attracting) and another that is hydrophobic (water-repelling). This property is crucial for the function of many membrane proteins and peptides.

Interpretation

In a helical wheel projection, hydrophobic residues often cluster on one side of the wheel, while hydrophilic residues cluster on the opposite side. This clustering can indicate the orientation of the helix in a membrane or its interaction with other molecules.

History

The concept of the helical wheel was first introduced in the 1980s as a tool for understanding the structural properties of alpha helices in proteins. It has since become a standard method in the field of protein structure analysis.

Related Concepts

• Alpha helix
• Protein secondary structure
• Amphipathic helix
• Membrane protein
• Peptide

See Also

• Ramachandran plot
• Hydrophobicity plot
• Protein folding