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Publication Abstract from PubMed

beta-Linked glucans such as cellulose and xyloglucan are important components of the cell wall of most dicotyledonous plants. These beta-linked glucans are constantly exposed to degradation by various endo-beta-glucanases from pathogenic bacteria and fungi. To protect the cell wall from degradation by such enzymes, plants secrete proteinaceous endo-beta-glucanases inhibitors, such as XEGIP in tomato. XEGIPs typically inhibit xyloglucanase, a member of the glycoside hydrolase 12 (GH12) family. XEGIPs are also found in legumes, including soybean and lupin. To date, tomato XEGIP has been well studied, whereas XEGIPs from legumes are less understood. Here we have determined the crystal structure of basic 7S globulin (Bg7S), a XEGIP from soybean, which represents the first three-dimensional structure of XEGIP. Bg7S forms a tetramer with pseudo-222 symmetry. Analytical centrifugation and size exclusion chromatography experiments reveal that assembly of Bg7S in solution depends on pH. The structure of Bg7S is similar to that of a xylanase inhibitor protein from wheat (TAXI) that inhibits GH11 xylanase. Surprisingly, Bg7S lacks inhibitory activity against not only GH11 but also GH12 enzymes. In addition, we found that XEGIPs from azukibean, yardlongbean and mungbean also had no impact on the activity of either GH12 or GH11 enzymes, indicating that legume XEGIPs generally do not inhibit these enzymes. We reveal the structural basis of why legume XEGIPs lack this inhibition activity. This study will provide significant clues to understanding the physiological role of Bg7S.

Crystal structure of basic 7S globulin, a XEGIP-like protein from soybean lacking inhibition activity against endo-beta-glucanase.,Yoshizawa T, Shimizu T, Yamabe M, Taichi M, Nishiuchi Y, Shichijo N, Unzai S, Hirano H, Sato M, Hashimoto H FEBS J. 2011 Apr 1. doi: 10.1111/j.1742-4658.2011.08111.x. PMID:21457461^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.