Crystal structure of a complex between Pseudomonas aeruginosa alkaline protease and its cognate inhibitor - Inhibition by a zinc-NH2 coordinative bond

Serralysins are a family of metalloproteases secreted by Gram-negative bact eria into the medium in the form of inactive zymogens. Usually, all serraly sin secretors have on the same operon a gene coding for a periplasmic 10-kD a protein, which is an inhibitor of the secreted protease. The recent chara cterization of the inhibitor of the alkaline protease from Pseudomonas aeru ginosa revealed a surprisingly low dissociation constant of 4 pM, contrary to earlier studies on homologous systems, where inhibition constants in the muM range were reported. To approach a more accurate understanding, the cr ystal structure of the complex between inhibitor and protease from P. aerug inosa was determined at 1.74 Angstrom resolution and refined to R-free = 0. 204. The structure reported here shows clearly that the N terminus of the i nhibitor forms a coordinative bond to the catalytic Zn2+ ion with a nitroge n-zinc distance of 2.17 Angstrom. We conclude that this interaction adds su bstantially to the complex stability and show also that similar interaction s are found in other metzincin-inhibitor complexes.