Metalloprotease

The most diverse class of catalytic types of proteases is Metalloproteases, named so based on the requirement of a divalent metal ion for their activity. They are distributed in bacteria, archaea, protozoa, fungi, plants, animals, and viruses. Based on the nature of the amino acid that completes the metal-binding site, they are grouped into 16 clans; e.g., clan MA has the se- quence HEXXH-E and clan MB corresponds to the motif HEXXH-H. However, with the exception as the metal atom binds at a motif other than the usual motif in one of the groups. the metalloproteases are also classified and divided based on the specificity of their action into four groups, (a) neutral, showing specificity for hydrophobic amino acids (b) alkaline, exhibiting broad specificity (c) Myxobacter I, specific towards having on either side of the cleavage bond the small amino acid residues (d) Myxobacter II, exhibit specificity for lysine residue on the amino side of the peptide bond. Metalloproteases undergo slighltly different as compared to the proteases described above. Enzymes requires the presence of bound divalent cations. Their activation is either can be via dialysis or through the addition of chelating agents. On the basis of the studies carried out on thermolysin-hydroxamic acid complex, it was deduced that the nucleophilic attack on the carbonyl carbon of the scissile peptide bond is mediated by Glu143 attacks and polarisation is carried by the Zn2+ ion. The site of metal binding (usually zinc) is partly to be localized within the motif His-Glu-Xaa-Xaa-His (HEXXH) (Rao et al., 1998).