alpha-2-macroglobulin-like protein 1 (C3 & PZP-like alpha-2-macroglobulin domain-containing protein 9, A2ML1, CPAMD9)

^[1]

Function

able to inhibit all 4 classes of proteinases by a unique 'trapping' mechanism
has a peptide stretch, called the 'bait region' which
contains specific cleavage sites for different proteinases
when a proteinase cleaves the bait region, a conformational change is induced in the protein which traps the proteinase
the entrapped enzyme remains active against low molecular weight substrates (activity against high molecular weight substrates is greatly diminished)
following cleavage in the bait region a thioester bond is hydrolyzed & mediates the covalent binding of the protein to the proteinase (putative)
displays inhibitory activity against chymotrypsin, papain, thermolysin, subtilisin A and, to a lesser extent, elastase but not trypsin
may play an important role during desquamation by inhibiting extracellular proteases

in epidermis, expressed predominantly in the granular layer at the apical edge of keratinocytes (at protein level)
also detected in placenta, testis & thymus but not in epithelia of kidney, lung, small intestine or colon
up-regulated during keratinocyte differentiation