In protein structure, a ferredoxin fold is a common ñ+ò protein fold with a signature òñòòñò secondary structure along its backbone. Structurally, the ferredoxin fold can be regarded as a long, symmetric hairpin that is wrapped once around, so that its two terminal ò-strands hydrogen-bond to the central two ò-strands, forming a four-stranded, antiparallel ò-sheet covered on one side by two ñ-helices.