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Directed in vitro evolution of bacterial expansin BsEXLX1 for higher cellulose binding and its consequences for plant cell wall‐loosening activities
Author(s) -
Hepler Nathan K.,
Cosgrove Daniel J.
Publication year - 2019
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1002/1873-3468.13528
Subject(s) - cell wall , expansin , mutant , cellulose , bacillus subtilis , bacterial cellulose , in vitro , chemistry , biochemistry , biophysics , microbiology and biotechnology , biology , bacteria , gene expression , genetics , gene
Expansins are cell wall‐loosening proteins found in all land plants and many microbial species. Despite homologous structures, bacterial expansins have much weaker cellulose binding and wall‐loosening activity than plant expansins. We hypothesized stronger cellulose binding would result in greater wall‐loosening activity and used in vitro evolution of Bacillus subtilis BsEXLX1 to test this hypothesis. Mutants with stronger binding generally had greater wall‐loosening activity, but the relationship was nonlinear and plateaued at ~ 40% higher than wild‐type. Mutant E191K exhibited stronger cellulose binding but failed to induce creep, evidently due to protein mistargeting. These results reveal the complexity of interactions between plant cell walls and wall‐modifying proteins, an important consideration when engineering proteins for applications in biofuel production and plant pathogen resistance.