Chitin-binding proteins in invertebrates and plants comprise a common chitin-binding structural motif

Area of Science:

• Biochemistry
• Structural Biology
• Evolutionary Biology

Background:

• Tachycitin is a 73-residue polypeptide with antimicrobial activity found in horseshoe crab (Tachypleus tridentatus) hemocytes.
• Understanding the structure of invertebrate chitin-binding proteins is crucial for evolutionary studies.

Purpose of the Study:

• To determine the first three-dimensional structure of an invertebrate chitin-binding protein, tachycitin.
• To investigate the structural relationship between invertebrate and plant chitin-binding proteins.

Main Methods:

• Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy was employed to determine the 3D structure of tachycitin.
• Tertiary structural analysis was performed to compare tachycitin with known chitin-binding proteins.

Main Results:

• The 3D structure of tachycitin revealed distinct N- and C-terminal domains.
• The N-terminal domain consists of a three-stranded beta-sheet, while the C-terminal domain features a two-stranded beta-sheet and a helical turn.
• The C-terminal structural motif shows significant similarity to the chitin-binding domain of plant chitin-binding proteins.

Conclusions:

• The determined structure of tachycitin provides experimental evidence supporting the hypothesis of convergent evolution between invertebrate and plant chitin-binding proteins.
• This finding highlights a potential shared evolutionary origin or adaptation mechanism for chitin-binding proteins across different kingdoms.