What type of protein structure is characterized by 7 transmembrane helices?

The correct answer identifies a type of integral membrane protein known for its distinctive structure featuring seven transmembrane helices. This configuration is a defining characteristic of G protein-coupled receptors (GPCRs), which belong to the Type III integral membrane proteins.

In the context of membrane proteins, Type III proteins traverse the lipid bilayer multiple times, and their arrangement allows them to interact with both the extracellular environment and the cytoplasm effectively. The seven transmembrane helices create a binding pocket that enables these proteins to detect various signaling molecules (ligands), leading to subsequent cellular responses.

This structural feature not only facilitates the protein's role in signal transduction but also contributes to its stability and functionality within the lipid membrane, which is essential for its interaction with other cellular components. In contrast, the other types of membrane proteins mentioned have different structural characteristics and do not feature this unique transmembrane configuration of seven helices.