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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.

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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.

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  • $\begingroup$ Since the β-sheet is part of the secondary structure of a protein shouldn't it only occur in a single polypeptide? $\endgroup$ – Αντώνιος Κελεσίδης May 22 '16 at 23:18
  • $\begingroup$ While you are correct that β-sheets are considered part of the secondary structure, they generically refer to the shape created by hydrogen bonds between parallel polypeptide chains, meaning that you can have β-sheets that require quaternary structure to emerge. $\endgroup$ – Niels Kornerup May 22 '16 at 23:59
  • $\begingroup$ I think I understand. So when the β-sheet structure is formed from one polypeptide chain, it is considered a part of the secondary stucture, while when more than one polypeptide chains form a beta sheet then it is considered a part of quaternary structure. Thank you very much for the clarification. $\endgroup$ – Αντώνιος Κελεσίδης May 23 '16 at 14:17
  • $\begingroup$ No problem, glad it helped. $\endgroup$ – Niels Kornerup May 23 '16 at 18:23

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