Current address: Department of Plant Biology, Cornell University, Ithaca, New York, NY 14853, USA.
Characterization of a tomato protein that inhibits a xyloglucan-specific endoglucanase
Article first published online: 23 APR 2003
The Plant Journal
Volume 34, Issue 3, pages 327–338, May 2003
How to Cite
Qin, Q., Bergmann, C. W., Rose, J. K. C., Saladie, M., Kolli, V. S. K., Albersheim, P., Darvill, A. G. and York, W. S. (2003), Characterization of a tomato protein that inhibits a xyloglucan-specific endoglucanase. The Plant Journal, 34: 327–338. doi: 10.1046/j.1365-313X.2003.01726.x
- Issue published online: 23 APR 2003
- Article first published online: 23 APR 2003
- Received 3 October 2002; revised 16 January 2003; accepted 30 January 2003.
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.