In a parallel β-sheet, what alignment do the C and N-termini have?

In a parallel β-sheet, the alignment of the C and N-termini is characterized by being aligned in the same direction. This means that both the N-terminal ends of the individual strands in the sheet point in one direction, while the C-terminals also point in that same direction. This alignment arises because, in a parallel arrangement, adjacent β-strands run in the same direction, allowing for the formation of hydrogen bonds that stabilize the structure.

The nature of the bonding between parallel strands leads to a relatively uniform orientation, contributing to the overall stability and structural integrity of the β-sheet. This arrangement allows for optimal hydrogen bonding between the carbonyl groups of the backbone of one strand and the amide hydrogens of the adjacent strand, creating a stable core structure that is crucial for the function of many proteins.

In contrast, other configurations like antiparallel β-sheets would see the N- and C-termini oriented in opposite directions, which emphasizes why the distinguishing characteristics of a parallel β-sheet are essential for understanding protein architecture and function.