1obb: Difference between revisions

Glycoside hydrolase family 4 represents an unusual group of glucosidases, with a requirement for NAD+, divalent metal cations, and reducing, conditions. The family is also unique in its inclusion of both alpha- and, beta-specific enzymes. The alpha-glucosidase A, AglA, from Thermotoga, maritima is a typical glycoside hydrolase family 4 enzyme, requiring NAD+, and Mn2+ as well as strongly reducing conditions for activity. Here we, present the crystal structure of the protein complexed with NAD+ and, maltose, refined at a resolution of 1.9 A. The NAD+ is bound to a typical, Rossman fold NAD+-binding site, and the nicotinamide moiety is localized, close to the maltose substrate. Within the active site the conserved, Cys-174 and surrounding histidines are positioned to play a role in the, hydrolysis reaction. The electron density maps indicate that Cys-174 is, oxidized to a sulfinic acid. Most likely, the strongly reducing conditions, are necessary to reduce the oxidized cysteine side chain. Notably, the, canonical set of catalytic acidic residues common to other glucosidases is, not present in the active site. This, combined with a high structural, homology to NAD-dependent dehydrogenases, suggests an unusual and possibly, unique mechanism of action for a glycoside-hydrolyzing enzyme.

1OBB is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Thermotoga_maritima Thermotoga maritima] with MAL and NAD as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Alpha-glucosidase Alpha-glucosidase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.20 3.2.1.20] Structure known Active Site: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1OBB OCA].  

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