Epsilon Open Archive

Abstract

The glycoside hydrolase Laminarinase 16A (Lam16A) from the white-rot fungus Phanerochaete chrysosporiumı is able to bind and cleave two different substrates in a specific manner. It has been called "non-specific", but we find that binding promiscuity and catalytic promiscuity better define this phenomenon. We have published high-resolution structures of wildtype Lam16A alone (Paper I) and in complex with oligosaccharide products from hydrolysis of laminarin and lichenan (up to 1.1 Å resolution) (Paper II) as well as structures of the catalytic nucleophile mutant Lam16A E115S in complex with laminariheptaose and alpha-laminariheptaosyl fluoride (Paper III, submitted). A beta-sandwich forms the substrate binding cleft, evenly open at both ends. The Lam16A ligand/complex structures, especially the catalytic mutants (Paper IV, manuscript), illustrate why two beta-1,3-linked glucose residues are required at the -2 and -1 subsites and why no beta-1,6-branch can be accomodated at these sites. Also, catalytic mutants enabled the trapping of substrate in the +1 subsite, showing how Lam16A can hydrolyze both beta-1,4- and beta-1,3-glycosidic bonds.