Crystal structures of Trichoderma reesei β-galactosidase reveal conformational changes in the active site.
We have determined the crystal structure of Trichoderma reesei (Hypocrea jecorina) β-galactosidase (Tr-β-gal) at a 1.2Å resolution and its complex structures with galactose, IPTG and PETG at 1.5, 1.75 and 1.4Å resolutions, respectively. Tr-β-gal is a potential enzyme for lactose hydrolysis in the dairy industry and belongs to family 35 of the glycoside hydrolases (GH-35). The high resolution crystal structures of this six-domain enzyme revealed interesting features about the structure of Tr-β-gal. We discovered conformational changes in the two loop regions in the active site, implicating a conformational selection-mechanism for the enzyme. In addition, the Glu200, an acid/base catalyst showed two different conformations which undoubtedly affect the pK(a) value of this residue and the catalytic mechanism. The electron density showed extensive glycosylation, suggesting a structure stabilizing role for glycans. The longest glycan showed an electron density that extends to the eighth monosaccharide unit in the extended chain. The Tr-β-gal structure also showed a well-ordered structure for a unique octaserine motif on the surface loop of the fifth domain.
Department of Chemistry, University of Eastern Finland, P.O. Box 111, FIN-80101 Joensuu, Finland.
Mirko
M
Maksimainen
Nina
N
Hakulinen
Johanna M
JM
Kallio
Tommi
T
Timoharju
Ossi
O
Turunen
Juha
J
Rouvinen
D020134:Catalytic Domain; D018360:Crystallography, X-Ray / Q000379:methods*; D005990:Glycerol / Q000378:metabolism; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014242:Trichoderma / Q000201:enzymology*; D001616:beta-Galactosidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D001616:beta-Galactosidase; D005990:Glycerol