Insights into role of the hydrogen bond networks in substrate recognition by UDP-GalNAc 4-epimerases

► Substrate recognition by UDP-GalNAc 4-epimerases is analyzed using sitedirected mutants. ► Most of the single point mutants retain the activity similar to the wild-type enzyme. ► Structure of the His305Ala mutant suggests the substrate-binding site to be fairly elastic. ► Graded loss in activity occurs as the mutations causing loss in hydrogen bonds accumulate.