B-sheet causes more rigidity R-C R-c CzO O…H=N RC-A N-Hee OrC R-C R-C R C=O c=o…H=N R R N一H…OEC R H-N cao…H-N C-RC-R C-R Hydrogen bonds oac N一Hoc between distant N一HorC amino acidsB-sheet causes more rigidity