Journal
ENZYME AND MICROBIAL TECHNOLOGY
Volume 92, Issue -, Pages 67-75Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.enzmictec.2016.06.017
Keywords
Lignocellulose loosening; BsEXLX1; Site-directed mutagenesis; Synergistic activity; Homologous modeling
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Funding
- National Natural Science Foundation of China [41271335, 31470191]
- Major State Basic Research Development Program of China (973 program) [2015CB150502]
- High Technology Research and Development Program of China (863 Program) [2012AA06A203]
- National Key Technology R D Program [2012BAC17B04]
- Science and Technology Project of Zhejiang Province [2013C3303, 2014C33019]
- Environmental Science Project of Zhejiang Province [2012B006]
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The bacterial expansin, BsEXLX1, has been studied as a model to understand the synergistic effect of expansins on lignocellulose degradation and the structure-function relationships of expansins. However, the specific mechanism is still poorly understood. In this study, the binding, synergistic and structural characteristics of BsEXDU for loosening the main components of lignocellulose: lignin, xylan, and cellulose, were further characterized. Results showed that BsEXLX1 preferentially binds to xylan over lignin or cellulose under various conditions. The binding of BsEXLX1 to all substrates increased linearly with the initial concentration of BsEXLX1. But the changing rate of binding (i.e., slope of the line; k value) varied with the incubation temperature. Interestingly, the binding of BsEXLX1 to substrates did not saturate. Mutating residue-125, 126 or 171 indicated their importance for binding, but they were less important for binding to xylan. Through binding assays and homologous modeling, it was concluded that residue 125 and 171 play more important roles in the structural maintenance of BsEXLX1. By comparing the synergistic activity of BsEXLX1 or its mutants, it was found that synergistic activity is not correlated with specific binding. All these results can lead deeper understand about the mechanism of wall loosening by expansins, and further promote the application of expansins in lignocellulose degradation. (C) 2016 Elsevier Inc. All rights reserved.
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