Alpha Helix Protein Structure Model

This Indigo® alpha helix model consists of 20 amino acid cores with a right handed chirality (clockwise spiral). Alpha helices are common in important biological proteins such as keratin (skin), hemoglobin (blood), myoglobin (muscle), & collagen (various tissues).

This model shows protein secondary structure based on 3.6 amino acid residues per turn & closely matches the scale of pitch distance 5.4 Å (angstroms), rise per residue of 1.5 Å & helix diameter of 6 Å. The backbone consists solely of alpha carbons and amino & carboxyl groups.

The “R” groups are indicated with a univalent green atom & face outward where they interact with other structures such as the major groove of our 12 base pair DNA double helix model.These "R" groups can be substituted with additional parts to show the most commonly occurring amino acid residues methionine, alanine, leucine, glutamate and lysine in the alpha helix polypeptide chain. These extra parts can make the steric hindrance more obvious when compared to the minor groove.

50mm bonds with white inserts represent the amide hydrogen atoms (N−HN-HN−H) of residues hydrogen bonded to carbonyl oxygen atoms (C=OC=OC=O) of another residue. This makes it clearer how the alpha helix structure is kept stable through these bonds (n to n+4) that are 4 residues away in the amino acid sequence.

Biological Importance of Alpha Helix Proteins in Cell Membranes

The hydrophobic side chains of the constituent amino acids of an alpha helix interact with the hydrophobic interior of the lipid bilayer which stabilizes its position within the cell membrane.

As transport proteins, alpha helices act as pathways to allow specific ions to move across cell membranes. These channels can be selective for water or act as gates for specific ions such as sodium, potassium, and calcium.

Bundles of alpha helices that span cell membranes change their conformation in response to ligand binding which in turn initiates intracellular signalling pathways. Some may even detect changes in light or pH & play a role in photosynthesis and respiration & electron transport as part of energy transduction.

Circular Dichroism Spectroscopy of Alpha Helices in Proteins

Circular dichroism (CD) spectroscopic analysis can inform the secondary structure, stability, and conformational changes in alpha proteins through comparing the interaction of polarized light the arrangement of peptide bonds. Alpha helix protein spectroscopic features peak in the far UV region of 190-250nm. Changes in the UV spectrum can help quantify a number of conditions affecting protein structure. This includes the extent of alpha helical content in a protein, the degree of its folding vs unfolding in response to temperature & pH or the binding of ligands.