Aromatic-Mediated Carbohydrate Recognition in Processive Serratia marcescens Chitinases

Gregg Beckham, Suvamay Jana, Anne Hamre, Patricia Wildberger, Matilde Holen, Vincent Eijsink, Morten Sorlie, Christina Payne

Research output: Contribution to journalArticlepeer-review

22 Scopus Citations

Abstract

Microorganisms use a host of enzymes, including processive glycoside hydrolases, to deconstruct recalcitrant polysaccharides to sugars. Processive glycoside hydrolases closely associate with polymer chains and repeatedly cleave glycosidic linkages without dissociating from the crystalline surface after each hydrolytic step; they are typically the most abundant enzymes in both natural secretomes and industrial cocktails by virtue of their significant hydrolytic potential. The ubiquity of aromatic residues lining the enzyme catalytic tunnels and clefts is a notable feature of processive glycoside hydrolases. We hypothesized that these aromatic residues have uniquely defined roles, such as substrate chain acquisition and binding in the catalytic tunnel, that are defined by their local environment and position relative to the substrate and the catalytic center. Here, we investigated this hypothesis with variants of Serratia marcescens family 18 processive chitinases ChiA and ChiB. We applied molecular simulation and free energy calculations to assess active site dynamics and ligand binding free energies. Isothermal titration calorimetry provided further insight into enthalpic and entropic contributions to ligand binding free energy. Thus, the roles of six aromatic residues, Trp-167, Trp-275, and Phe-396 in ChiA, and Trp-97, Trp-220, and Phe-190 in ChiB, have been examined. We observed that point mutation of the tryptophan residues to alanine results in unfavorable changes in the free energy of binding relative to wild-type. The most drastic effects were observed for residues positioned at the "entrances" of the deep substrate-binding clefts and known to be important for processivity. Interestingly, phenylalanine mutations in ChiA and ChiB had little to no effect on chito-oligomer binding, in accordance with the limited effects of their removal on chitinase functionality.

Original languageAmerican English
Pages (from-to)1236-1249
Number of pages14
JournalJournal of Physical Chemistry B
Volume120
Issue number7
DOIs
StatePublished - 25 Feb 2016

Bibliographical note

Publisher Copyright:
© 2016 American Chemical Society.

NREL Publication Number

  • NREL/JA-5100-66036

Keywords

  • ChiA
  • ChiB
  • Serratia marcescens

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