I know that a β-strand forms bonds with another β-strands and so on and thus a β-sheet is formed, but are those strands from the same polypeptide? And does their distance matter? Do they have to be close or it is not necessary? Thanks in advance.
A β-sheet is formed as the result of hydrogen bonding between the β-strands in the secondary structure of a protein. The hydrogen bonding occurs between the carbonyl oxygen and the amide hydrogen of adjacent strands, and can take on either a parallel or an antiparallel arrangement. As can be seen in the diagrams, antiparallel arrangement of the polypeptides results in more stable interactions between the strands, but both arrangements are possible and can be found in nature. Regardless of the type of arrangement, β-sheets can be formed by either interactions between different polypeptides or intramolecular hydrogen bonding within a single polypeptide. In fact, intramolecular hydrogen bonding creating β-sheets is really common. One example of it occurring in β hairpin motifs.