Fig. 7
Active site configuration at acidic and alkaline pH. Comparison of the active site configuration at two extreme pH conditions by superposing the crystal structures of F. oxysporum Xyl2 obtained at pH 5.0 (cyan) with the neutron crystal structures of T. reesei Xyl2 at pD 4 (olive green), pD 4.4 (light green) a or pD 8 (pale yellow) b The rotameric conformations of Tyr73 and Glu177 (numbering according to T. reesei Xyl2) are flipped over at the two extreme pH values, with catalytically competent conformations being observed only at alkaline pH conditions (b)