Primary structure and evolution of calcium-activated neutral protease (CANP)

The amino acid sequences of two subunits (80K and 30K) of calcium-activated neutral protease (CANP) were examined to clarify the structure-function relationship of CANP. The 80K subunit is composed of four clear domains (I–IV from the N-terminus). Domain II is a cysteine proteinase domain homologous to cathepsins B, L, and H. Domain IV is a calcium binding domain with four consecutive EF-hand structures known as typical calcium-binding sites found in calmodulin. The 30K subunit also has a clear domain structure (two domains). The N-terminal domain, a Gly-rich hydrophobic domain, probably determines the location of CANP through association with cellular membrane. The C-terminal domain is a calmodulinlike calcium-binding domain highly homologous to IV in the 80K subunit. The protease activity ascribable to II is regulated by 2 moles of built-in calmodulins, though its precise regulation mechanism is unknown. These results are discussed together with the molecular evolution of CANP on the basis of the gene structures of the two subunits.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.