PMID: 23137336

Authors:

Wu M, Nerinckx W, Piens K, Ishida T, Hansson H, Sandgren M, Stahlberg J

Title:

Rational design, synthesis, evaluation and enzyme-substrate structures of improved fluorogenic substrates for family 6 glycoside hydrolases.

Journal:

FEBS J. 2013 Jan;280(1):184-98. doi: 10.1111/febs.12060. Epub 2012 Dec 7.

Abstract:

Methylumbelliferyl-beta-cellobioside (MUF-G2) is a convenient fluorogenic substrate for certain beta-glycoside hydrolases (GH). However, hydrolysis of the aglycone is poor with GH family 6 enzymes (GH6), despite strong binding. Prediction of the orientation of the aglycone of MUF-G2 in the +1 subsite of Hypocrea jecorina Cel6A by automated docking suggested umbelliferyl modifications at C4 and C6 for improved recognition. Four modified umbelliferyl-beta-cellobiosides [6-chloro-4-methyl- (ClMUF); 6-chloro-4-trifluoromethyl- (ClF3MUF); 4-phenyl- (PhUF); 6-chloro-4-phenyl- (ClPhUF)] were synthesized and tested with GH6, GH7, GH9, GH5 and GH45 cellulases. Indeed the rate of aglycone release by H. jecorina Cel6A was 10-150 times higher than with MUF-G2, although it was still three orders of magnitude lower than with H. jecorina Cel7B. The 4-phenyl substitution drastically reduced the fluorescence intensity of the free aglycone, while ClMUF-G2 could be used for determination of k(cat) and K(M) for H. jecorina Cel6A and Thermobifida fusca Cel6A. Crystal structures of H. jecorina Cel6A D221A mutant soaked with the MUF-, ClMUF- and ClPhUF-beta-cellobioside substrates show that the modifications turned the umbelliferyl group 'upside down', with the glycosidic bond better positioned for protonation than with MUF-G2. DATABASE: Structural data have been submitted to the Protein Data Bank under accession numbers pdb 4AU0, 4AX7, 4AX6 STRUCTURED DIGITAL ABSTRACT: * http://mint.bio.uniroma2.it/mint/search/interaction.do?interactionAc=MINT-7260296 * Cel6A and Cel6A bind by x-ray crystallography (View Interaction: 1, 2).