Question

1) Predict how collagen's function would be altered if collagen was a globular protein.

2) Trace the path of the protein shown below and label the N and C termini.

Answer 1

1. Collagen is a structural protein, and a fibrous protein. Its ability to impart mechanical strength comes from its triple-helix structure, which is bonded to each other using hydrogen bonds, and further arranged as bundles, all joined by cross-links. The fibrous nature provides large surface area for all these interactions. But if it were globular, the structure would have been compact, making such a network of extensive covalent and non-covalent interactions impossible. Globular proteins also happen to be soluble, unlike fibrous proteins, which are insoluble. Collagen is part of the extracellular matrix, bathed in extracellular fluid. In this scenario, a soluble protein can not provide this mechanical support.

2. The ribbon structure of a protein, represents the peptide bond and the alpha carbon skeleton. The peptide bond is directional, moving from N- to C-terminus. This direction can be inferred from the arrowheads pointing to the C-teminus, traveling from the N-terminus to the C-terminus. The termini are labelled in the diagram below:

C-terminus N-terminus