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Reply to Cosgrove: Non-enzymatic action of expansins

Open AccessPublished:May 08, 2020DOI:https://doi.org/10.1074/jbc.RL120.013432
      In our computational study, we use molecular simulations to substantiate a hypothetical mechanism for glycosidic bond cleavage in the presence of a single catalytic acid at the active site of the mutant D10N HiCel45A. In addition to discussing this plausible mechanism from the context of structurally related MltA lytic transglycosylase and subfamily C GH45s, we also suggest the implications of the plausible mechanism for our current understanding of the action of expansins and lytic transglycosylases. As correctly pointed out by Professor Cosgrove (
      • Cosgrove D.J.
      Non-enzymatic action of expansins.
      ), there is large body of evidence, a significant portion of which was regrettably not discussed in our paper, that suggests that expansins are incapable of lytic action on polysaccharide substrates. Whereas these insights do not change the results or the conclusions of our article, we would like to thank Professor Cosgrove for these additional insights. In particular, our main point with respect to expansins is that our results suggest the possibility that expansins are capable of nonhydrolytic lytic activity. Our intention was not to suggest this was the mechanism of expansins, but that it should be considered based on our results and the similarity of the active sites.
      The molecular mechanisms of how expansins enable cell wall expansion remains to be fully understood. Whereas our proposed mechanism resulting in the formation of the 1,6-anhdro product might be found in expansins and might contribute to the mode of action of expansins, we would like to emphasize that the intent of this study was only to suggest this as a possibility that requires thorough experimental verification and validation. Our intent in relating the mechanistic predictions to expansins was only to stimulate discussion that could lead to alternative directions for future experimental investigations, which may improve our molecular-level understanding of expansin action.

      Reference

        • Cosgrove D.J.
        Non-enzymatic action of expansins.
        J. Biol. Chem. 2020; 295: 6782

      Linked Article

      • Non-enzymatic action of expansins
        Journal of Biological ChemistryVol. 295Issue 19
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          From their simulations of endoglucanase Cel45A, Bharadwaj et al. (1) propose that structurally related expansins and MltA may cut glycan backbones without generating reducing ends. This is tenable for MltA, a peptidoglycan lytic transglycosylase whose action produces nonreducing 1,6-anhydro products, but is untenable for expansins.
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