Identification of residues important for NAD+binding by theThermotoga maritimaα‐glucosidase AglA, a member of glycoside hydrolase family 4

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Abstract
The NAD+-requiring enzymes of glycoside hydrolase family 4 (GHF4) contain a region with a conserved Gly-XXX-Gly-Ser (GXGS) motif near their N-termini that is reminiscent of the fingerprint region of the Rossmann fold, a conserved structural motif of classical nicotinamide nucleotide-binding proteins. The function of this putative NAD+-binding motif in the α-glucosidase AglA of Thermotoga maritima was probed by directed mutagenesis. The K d for NAD+ of the AglA mutants G10A, G12A and S13A was increased by about 300-, 5-, and 9-fold, respectively, while their K m for p-nitrophenyl-α-glucopyranoside was not seriously affected. The results indicate that the GXGS motif is indeed important for NAD+ binding by the glycosidases of GHF4.