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

Tetsuya Suetake,Kunio Hikichi,Shun-ichiro Kawabata,Sadaaki Iwanaga,Katsutoshi Nitta,Kazunori Miura,Keiichi Kawano,Sakae Tsuda

doi:10.1074/jbc.c000184200

Abstract

Tachycitin, a 73-residue polypeptide having antimicrobial activity is present in the hemocyte of horseshoe crab (Tachypleus tridentatus). The first three-dimensional structure of invertebrate chitin-binding protein was determined for tachycitin using two-dimensional nuclear magnetic resonance spectroscopy. The measurements indicate that the structure of tachycitin is largely divided into N- and C-terminal domains; the former comprises a three-stranded beta-sheet and the latter a two-stranded beta-sheet following a short helical turn. The latter structural motif shares a significant tertiary structural similarity with the chitin-binding domain of plant chitin-binding protein. This result is thought to provide faithful experimental evidence to the recent hypothesis that chitin-binding proteins of invertebrates and plants are correlated by a convergent evolution process.

Highlights

From the ‡Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 0600810, §Bioscience and Chemistry Division, Hokkaido National Industrial Research Institute, Sapporo 0628517, ʈDepartment of Biology, Kyushu University, Fukuoka 812-8581, **Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Tokyo 101-0062, and ‡‡Department of Structural Biology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama 930-0194, Japan
This advanced knowledge has been provided for the plant chitin-binding proteins, less is known for the invertebrate chitin-binding proteins including tachycitin (1, 13–16)
The structural determination was performed (Table I) using NMR-derived 1,070 experimental restraints, on the basis of the whole assignments of the 1H resonances of tachycitin at pH 4.2 and at 30 °C, which were deposited to BioMagResBank with the accession number of 4290

Summary

Accelerated Publication

The measurements indicate that the structure of tachycitin is largely divided into N- and C-terminal domains; the former comprises a three-stranded ␤-sheet and the latter a two-stranded ␤-sheet following a short helical turn The latter structural motif shares a significant tertiary structural similarity with the chitin-binding domain of plant chitin-binding protein. This result is thought to provide faithful experimental evidence to the recent hypothesis that chitin-binding proteins of invertebrates and plants are correlated by a convergent evolution process. It has been well demonstrated that this domain is indispensable for the antimicrobial activity and exhibits a significant conservation in primary sequence (Ͼ40%) and in three-dimensional (3D) structure (9 –12) This advanced knowledge has been provided for the plant chitin-binding proteins, less is known for the invertebrate chitin-binding proteins including tachycitin (1, 13–16). The present study determines the solution structure of tachycitin using NMR spectroscopy, which provides the first 3D structural information of invertebrate chitin-binding protein

EXPERIMENTAL PROCEDURES

RMSD from ideal covalent geometry

RESULTS AND DISCUSSION