TY - JOUR
T1 - How Family 26 Glycoside Hydrolases Orchestrate Catalysis on Different Polysaccharides
AU - Taylor, E.J.
AU - Goyal, A.
AU - Guerreiro, C.I.P.D.
AU - Prates, J.A.M.
AU - Money, V.A.
AU - Ferry, N.
AU - Morland, C.
AU - Planas, A.
AU - Macdonald, J.
AU - Stick, Robert
AU - Gilbert, H.J.
AU - Fontes, C.M.G.A.
AU - Davies, G.J.
PY - 2005
Y1 - 2005
N2 - One of the most intriguing features of the 90 glycoside hydrolase families (GHs) is the range of specificities displayed by different members of the same family, whereas the catalytic apparatus and mechanism are often invariant. Family GH26 predominantly comprises beta-1,4 mannanases; however, a bifunctional Clostridium thermocellum GH26 member (hereafter CtLic26A) displays a markedly different specificity. We show that CtLic26A is a lichenase, specific for mixed (Glc beta 1,4Glc beta 1,4Glc beta 1,3)(n) oligo- and polysaccharides, and displays no activity on manno-configured substrates or beta-1,4-linked homopolymers of glucose or xylose. The three-dimensional structure of the native form of CtLic26A has been solved at 1.50-angstrom resolution, revealing a characteristic (beta/alpha)s barrel with Glu-109 and Glu-222 acting as the catalytic acid/base and nucleophile in a double-displacement mechanism. The complex with the competitive inhibitor, Glc-beta-1,3-isofagomine (K-i 1 mu M), at 1.60 angstrom sheds light on substrate recognition in the -2 and -1 subsites and illuminates why the enzyme is specific for lichenan-based substrates. Hydrolysis of beta-mannosides by GH26 members is thought to proceed through transition states in the B2+5 (boat) conformation in which structural distinction of glucosides versus mannosides reflects not the configuration at C2 but the recognition of the pseudoaxial O3 of the B2+5 conformation. We suggest a different conformational itinerary for the GH26 enzymes active on gluco-configured substrates.
AB - One of the most intriguing features of the 90 glycoside hydrolase families (GHs) is the range of specificities displayed by different members of the same family, whereas the catalytic apparatus and mechanism are often invariant. Family GH26 predominantly comprises beta-1,4 mannanases; however, a bifunctional Clostridium thermocellum GH26 member (hereafter CtLic26A) displays a markedly different specificity. We show that CtLic26A is a lichenase, specific for mixed (Glc beta 1,4Glc beta 1,4Glc beta 1,3)(n) oligo- and polysaccharides, and displays no activity on manno-configured substrates or beta-1,4-linked homopolymers of glucose or xylose. The three-dimensional structure of the native form of CtLic26A has been solved at 1.50-angstrom resolution, revealing a characteristic (beta/alpha)s barrel with Glu-109 and Glu-222 acting as the catalytic acid/base and nucleophile in a double-displacement mechanism. The complex with the competitive inhibitor, Glc-beta-1,3-isofagomine (K-i 1 mu M), at 1.60 angstrom sheds light on substrate recognition in the -2 and -1 subsites and illuminates why the enzyme is specific for lichenan-based substrates. Hydrolysis of beta-mannosides by GH26 members is thought to proceed through transition states in the B2+5 (boat) conformation in which structural distinction of glucosides versus mannosides reflects not the configuration at C2 but the recognition of the pseudoaxial O3 of the B2+5 conformation. We suggest a different conformational itinerary for the GH26 enzymes active on gluco-configured substrates.
U2 - 10.1074/jbc.M506580200
DO - 10.1074/jbc.M506580200
M3 - Article
C2 - 15987675
VL - 280
SP - 32761
EP - 32767
JO - The Journal of Biological Chemistry
JF - The Journal of Biological Chemistry
SN - 0021-9258
IS - 38
ER -