Proteinase inhibitors and dendrotoxins. Sequence classification, structural prediction and structure/activity.

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Dendrotoxins are presynaptically active toxins found in mamba snake venom.
• Kunitz-type proteinase inhibitors share homologous sequences with dendrotoxins.
• Understanding the structural and functional relationship between these molecules is crucial for elucidating their biological roles.

Purpose of the Study:

• To systematically compare the amino acid sequences of dendrotoxins and Kunitz proteinase inhibitors.
• To identify key amino acid changes responsible for the functional divergence between dendrotoxins and proteinase inhibitors.
• To predict structural features and propose a mechanism of action for dendrotoxins.

Main Methods:

• Systematic sequence comparison of dendrotoxins and homologous proteinase inhibitors.
• Analysis of conserved sequence segments, particularly the antiprotease site.
• Secondary structure prediction focusing on the antiprotease site region.
• Structure-activity relationship analysis based on existing crystal structures of inhibitor-enzyme complexes.

Main Results:

• Relatively few amino acid substitutions can convert a proteinase inhibitor into a dendrotoxin, abolishing antiprotease activity.
• Dendrotoxins are clearly distinguished from known inhibitors when focusing on antiprotease site sequences and predicted secondary structures.
• Unlike proteinase inhibitors, dendrotoxins may specifically coordinate the catalytic histidine residues of serine proteases.

Conclusions:

• Dendrotoxins and proteinase inhibitors likely share a common evolutionary origin.
• Structural and functional differences suggest distinct mechanisms of action, with dendrotoxins potentially targeting serine proteases via histidine coordination.
• The presynaptic target of dendrotoxins is hypothesized to be an uncharacterized serine protease member.