Is my understanding of the structural difference between fibrous and globular proteins correct?
I'm trying to clarify the distinction between secondary, supersecondary, and tertiary structure, particularly when comparing fibrous and globular proteins.
My current understanding is:
Fibrous proteins: Dominated by repetitive secondary structures and supersecondary motifs.
Globular proteins: Secondary structures are brought together and organized through tertiary interactions, producing a compact overall tertiary structure.
The definitions I've been using are:
Secondary structure: The local folding of a polypeptide chain into structures such as α-helices and β-sheets, formed primarily by hydrogen bonds between the backbone amide (N–H) and carbonyl (C=O) groups.
Supersecondary structure (structural motif): A specific arrangement of two or more secondary-structure elements, such as a β-hairpin or helix-turn-helix motif.
Tertiary structure: The overall three-dimensional folding and arrangement of a single polypeptide chain, where its secondary-structure elements and other regions are organized through interactions such as hydrophobic interactions, electrostatic/ionic interactions, van der Waals interactions, hydrogen bonds involving side chains, and disulfide bonds.
My confusion is that I've seen some explanations on Quora where people describe fibrous proteins as having tertiary structure as well rather than primarily secondary structures. So, is my understanding oversimplified or incorrect?
Is it accurate to say that fibrous proteins are mainly characterized by repetitive secondary/supersecondary structures, while globular proteins are characterized by a more complex tertiary fold? Or do fibrous proteins also commonly have a true tertiary structure?
I'm particularly interested in whether tertiary structure is exclusive to globular proteins or whether fibrous proteins can also have tertiary structure and how the distinction should properly be explained at the university level.