The secondary structure of a protein is the local folded shape adopted by regions of the peptide chain, such as the α-helix and the β-sheet. These regular shapes are held in place by hydrogen bonds between the backbone groups of the chain. The secondary structure lies between the primary sequence and the overall tertiary fold.

蛋白质的二级结构是肽链各局部区域所采取的折叠形状,如 α-螺旋和 β-折叠。这些规则形状由链主链基团之间的氢键维持。二级结构介于一级序列与整体三级折叠之间。