Design of a new protease inhibitor by the manipulation of the bait region of alpha 2-macroglobulin: inhibition of the tobacco etch virus protease by mutant alpha 2-macroglobulin.

Human alpha 2-macroglobulin (alpha 2M) inhibits a broad spectrum of proteases by changing its conformation and physically confining the enzyme. The inhibitory spectrum of alpha 2M is defined by a stretch of 39 amino acids, the bait region, located near the middle of the alpha 2M monomers. To investigate whether a new inhibitory specificity can be introduced by the manipulation of the bait region, recombinant alpha 2M (r alpha 2M) was produced in which the primary cleavage site was replaced by a heptapeptide containing the cleavage specificity of tobacco etch virus (TEV) protease. This protease is not inhibited by wild-type alpha 2M. The r alpha 2M, produced in an episomal expression system, was fully functional and able to inhibit the tobacco etch virus protease according to its normal 'trap' mechanism. The manipulation of the bait region of alpha 2M thus allows the design of new, specific protease inhibitors.