​Given below are four topology diagrams corresponding to different proteins. N and C denote the N-terminal and C-terminal ends of the protein chains.

Which one of the following statements is CORRECT?

Correct option is D

1. Topology diagrams show the arrangement of β-strands and their connectivity in protein structures.
2. The direction of arrows represents the N-terminal to C-terminal direction.
3. Proteins with the same fold have a similar arrangement and connectivity of β-strands.

Diagram A

• Four β-strands in an antiparallel arrangement.
• Specific connectivity pattern of loops between strands.
• N-terminal at the bottom left, C-terminal at the bottom right.

Diagram B

• Different arrangement of β-strands compared to A.
• Loops are positioned differently, altering the connectivity.
• This means B has a different fold from A.

Diagram C

• Four β-strands in an antiparallel arrangement, similar to A.
• Only difference: The N-terminal and C-terminal positions are swapped.
• Since topology (strand connectivity) is the same, it belongs to the same fold as A.

Diagram D

• Different connectivity compared to A and C.
• Strands and loops are arranged differently than in A and C.
• Thus, D has a different fold from A and C.