Which of the following is NOT a frequently seen protein motif?

The alpha helix is indeed a well-known structural motif found in numerous proteins, playing a critical role in secondary structure formation. It is characterized by a right-handed coil of amino acids, where the backbone forms hydrogen bonds between the carbonyl oxygen of one residue and the amide hydrogen of another, typically four residues down the chain. This motif is a fundamental component of many proteins and is crucial for the stability of their overall conformation.

In contrast, the other motifs listed, such as coiled coil, zinc finger, and beta barrel, represent specific structural arrangements that are associated with distinct functional roles and molecular interactions. The coiled coil is important for protein-protein interactions and is commonly found in fibrous proteins. The zinc finger motif is often involved in DNA binding, enabling proteins to interact with nucleic acids and regulate gene expression. The beta barrel is a structure formed by beta sheets that often serves as a pore in membrane proteins.

Choosing the alpha helix as the option that is not frequently seen as a motif is misleading because it is one of the most prevalent and crucial motifs in protein structure, contrary to the assertion made in your selection.