Protease inhibitor (biology)

In biology and biochemistry, protease inhibitors are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins.

In medicine, protease inhibitor is often used interchangeably with alpha 1-antitrypsin (A1AT, which is abbreviated PI for this reason). A1AT is indeed the protease inhibitor most often involved in disease, namely in alpha 1-antitrypsin deficiency.

Classification
Protease inhibitors may be classified either by the type of protease they inhibit, or by their mechanism of action. In 2004 Rawlings and colleagues introduced a classification of protease inhibitors based on similarities detectable at the level of amino acid sequence. This classification initially identified 48 families of inhibitors that could be grouped into 26 related superfamily (or clans) by their structure. According to the MEROPS database there are now 85 families of inhibitors. These families are named with an I followed by a number, for example, I14 contains hirudin-like inhibitors.

By protease
Classes of proteases are:


 * Aspartic protease inhibitors
 * Cysteine protease inhibitors
 * Metalloprotease inhibitors
 * Serine protease inhibitors (serpins)
 * Threonine protease inhibitors
 * Trypsin inhibitors
 * Kunitz STI protease inhibitor

By mechanism
Classes of inhibitor mechanisms of action are:


 * Suicide inhibitor
 * Transition state inhibitor
 * Protein protease inhibitor (see serpins)
 * Chelating agents

Compounds

 * Aprotinin
 * Bestatin
 * Calpain inhibitor I and II
 * Chymostatin
 * E-64
 * Leupeptin (N-acetyl- L -leucyl- L -leucyl- L -argininal)
 * alpha-2-Macroglobuline
 * Pefabloc SC
 * Pepstatin
 * PMSF (phenylmethanesulfonyl fluoride)
 * TLCK
 * Trypsin inhibitors