Protease Inhibitors from Marine Venomous Animals and Their Counterparts in Terrestrial Venomous Animals

Abstract

The Kunitz-type protease inhibitors are the best-characterized family of serine protease inhibitors, probably due to their abundance in several organisms. These inhibitors consist of a chain of ~60 amino acid residues stabilized by three disulfide bridges, and was first observed in the bovine pancreatic trypsin inhibitor (BPTI)-like protease inhibitors, which strongly inhibit trypsin and chymotrypsin. In this review we present the protease inhibitors (PIs) described to date from marine venomous animals, such as from sea anemone extracts and Conus venom, as well as their counterparts in terrestrial venomous animals, such as snakes, scorpions, spiders, Anurans, and Hymenopterans. More emphasis was given to the Kunitz-type inhibitors, once they are found in all these organisms. Their biological sources, specificity against different proteases, and other molecular blanks (being also K+ channel blockers) are presented, followed by their molecular diversity. Whereas sea anemone, snakes and other venomous animals present mainly Kunitz-type inhibitors, PIs from Anurans present the major variety in structure length and number of Cys residues, with at least six distinguishable classes. A representative alignment of PIs from these venomous animals shows that, despite eventual differences in Cys assignment, the key-residues for the protease inhibitory activity in all of them occupy similar positions in primary sequence. The key-residues for the K+ channel blocking activity was also compared.

Kunitz-Type Peptide HCRG21 from the Sea Anemone Heteractis crispa Is a Full Antagonist of the TRPV1 Receptor

“…Sea anemone (phylum Cnidaria, class Anthozoa) venom is a rich source of proteinaceous toxins acting on ion channels such as voltage-gated sodium and potassium channels, and the TRPV1 [1,2,3,4,5] as well as a lot of protease inhibitors belonging, mainly, to a numerous BPTI/Kunitz-type family [6]. The peptides of this family have an ancient Kunitz fold and some of them are characterized by a unique and intriguing feature of dual functionality since they inhibit both proteases and ion channels [7,8,9,10].…”

Discoveries of Serine Protease Inhibitors from Scorpions

“…Consequently, a distinct disulfide bridge may be generated [22,39]. Additionally, among other scorpion protease inhibitors, recombinant BmKTT-2 was found to possess eight cysteine residues connected by four disulfide bridges, which is different architectural property from all known Kunitz-type animal toxins [11,39] (Figure 1). …”

“…Nevertheless, rLmKTT-1b along with the scorpion peptides rLmKTT-1a, rLmKTT-1c, and rBmKTT-1 [11,39] contain a unique cysteine framework, different from the classical Kunitz-type motif, where the normal C2-C4 disulfide bridge is absent, but two additional cysteine residues are present at the C-terminus of the mature peptide, which might create a new disulfide bond. Consequently, a distinct disulfide bridge may be generated [22,39].…”

“…Nevertheless, rLmKTT-1b along with the scorpion peptides rLmKTT-1a, rLmKTT-1c, and rBmKTT-1 [11,39] contain a unique cysteine framework, different from the classical Kunitz-type motif, where the normal C2-C4 disulfide bridge is absent, but two additional cysteine residues are present at the C-terminus of the mature peptide, which might create a new disulfide bond. Consequently, a distinct disulfide bridge may be generated [22,39]. Additionally, among other scorpion protease inhibitors, recombinant BmKTT-2 was found to possess eight cysteine residues connected by four disulfide bridges, which is different architectural property from all known Kunitz-type animal toxins [11,39] (Figure 1).…”

A Low Molecular Weight Protein from the Sea Anemone <em>Anemonia viridis</em> with an Anti Angiogenic Activity

“…They have different structural scaffolds regarding their pharmacological targets. Active principles binding on ionic channel are characterized by three beta strands [7], while those binding on enzymes such as the family of Kunitz-type inhibitors have two beta strands and an alpha helix [8]. Surprisingly the sea anemone toxin Bg1 can compete at nano molar concentrations on the same pharmacological site on sodium channel than the Aah II scorpion toxin with a scaffold completely different [9].…”