4.1.2.19 | structure established at 1.35 A resolution in a crystal form that is obtained by a surface mutation and has one subunit of the C4-symmetric tetramer in the asymmetric unit. Crystals of the wild-type enzyme with their 20 crystallographically asymmetric subunits diffract to only 2.7 A resolution are much too complex for a convenient analysis of structural modifications. For both reasons, a more suitable crystal form is obtained by producing the six point mutants W8T, Q51R, Q52E, D98Y, E192A and E254R at the protein surface far away from the active center |