Serine Proteases

Serine proteases are present in virtually all organisms and function both inside and outside the cell; they exist as two families, the 'trypsin-like' and the 'subtilisin-like'. They are called the serine proteases for two reasons:

The mammalian serine proteases comprise a structurally similar family of proteins with a diversity of functions. Some examples of serine proteases are: All the mammalian serine proteases have a common 3D structure, although there are quite significant differences in some regions of the surface, reflecting the different physiological functions, and hence need for different interactions with different molecules. They all have the same catalytic mechanism. The sequence and structural homology among proteins reveal their evolutionary relationships. The great similarities among chymotrypsin, trypsin and elastase indicate that these proteins evolved through gene duplications of an ancestral serine protease followed by the divergent evolution of the resulting enzymes.
Subtilisin (originally isolated from Bacillus subtilis is a serine protease whose primary and tertiary structures bear no discernible relationships to those of chymotrypsin. Yet the active site groups of these two enzymes are essentially identical and their relative three-dimentional positions are nearly indistinguishable. The orders of the corresponding active site residues in the amino acid sequences of the two enzymes are quite different (Ser-195, His-57, Asp-102 in chymotrypsin, trypsin and elastase; Ser-221, His-64, Asp-32 in the bacterial subtilisin). Chymotrypsin and subtilisin apparently constitute a remarkable example of convergent evolution.
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Robert Janowski robert@leucine.ibch.poznan.pl