Characterization of a tomato protein that inhibits a xyloglucan‐specific endoglucanase

• Published in: The Plant journal : for cell and molecular biology 2003-05, Vol.34 (3), p.327-338
• Main Authors: Qin, Qiang, Bergmann, Carl W., Rose, Jocelyn K. C., Saladie, Montserrat, Kolli, V. S. Kumar, Albersheim, Peter, Darvill, Alan G., York, William S.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Biological and medical sciences; Cells, Cultured; Cellulase - antagonists & inhibitors; Cellulase - metabolism; Cloning, Molecular; DNA, Complementary - chemistry; DNA, Complementary - genetics; endoglucanase; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; fungi; Glucans; Glycoproteins - genetics; Glycoproteins - metabolism; Glycoproteins - pharmacology; inhibitor; Lycopersicon esculentum - genetics; Lycopersicon esculentum - metabolism; Molecular Sequence Data; pathogenesis; Pathology, epidemiology, host-fungus relationships. Damages, economic importance; Phytopathology. Animal pests. Plant and forest protection; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Proteins - pharmacology; plants; Polysaccharides - metabolism; Protein Binding; Protein Interaction Mapping; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Xylans; xyloglucan
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.2003.01726.x

Summary A basic, 51 kDa protein was purified from suspension‐cultured tomato and shown to inhibit the hydrolytic activity of a xyloglucan‐specific endoglucanase (XEG) from the fungus Aspergillus aculeatus. The tomato (Lycopersicon esculentum) protein, termed XEG inhibitor protein (XEGIP), inhibits XEG activity by forming a 1 : 1 protein:protein complex with a Ki ≈ 0.5 nm. To our knowledge, XEGIP is the first reported proteinaceous inhibitor of any endo‐β‐1,4‐glucanase, including the cellulases. The cDNA encoding XEGIP was cloned and sequenced. Database analysis revealed homology with carrot extracellular dermal glycoprotein (EDGP), which has a putative role in plant defense. XEGIP also has sequence similarity to ESTs from a broad range of plant species, suggesting that XEGIP‐like genes are widely distributed in the plant kingdom. Although Southern analysis detected only a single XEGIP gene in tomato, at least five other XEGIP‐like tomato sequences have been identified. Similar small families of XEGIP‐like sequences are present in other plants, including Arabidopsis. XEGIP also has some sequence similarity to two previously characterized proteins, basic globulin 7S protein from soybean and conglutin γ from lupin. Several amino acids in the XEGIP sequence, notably 8 of the 12 cysteines, are generally conserved in all the XEGIP‐like proteins we have encountered, suggesting a fundamental structural similarity. Northern analysis revealed that XEGIP is widely expressed in tomato vegetative tissues and is present in expanding and maturing fruit, but is downregulated during ripening.