alt=Diagram of<unk>  states All<unk> s share a common structure (or fold), despite their varied functions. All typically have three β-sheets (named A, B and C) and eight or nine α-helices (named hA–hI). The most significant regions to<unk>  function are the A-sheet and the reactive centre loop (RCL). The A-sheet includes two β-strands that are in a parallel orientation with a region between them called the 'shutter', and upper region called the 'breach'. The RCL forms the initial interaction with the target protease in inhibitory molecules. Structures have been solved showing the RCL either fully exposed or partially inserted into the A-sheet, and<unk> s are thought to be in dynamic equilibrium between these two states. The RCL also only makes temporary interactions with the rest of the structure, and is therefore highly flexible and exposed to the solvent. The<unk>  structures that have been determined cover several different conformations, which has been necessary for the understanding of their multiple-step mechanism of action. Structural biology has therefore played a central role in the understanding of<unk>  function and biology.
Serpin
Thrombin
Immunoevasin
Kallikrein
Plasminogen 
Hemostat
Anordrin
Tetanospasmin