FIG. 2.

Comparison of average apoenzyme structures of Glu104 and Lys104 variants. Comparison was carried out by superpositioning, using the Cα atoms for the root mean square fit. Some of the secondary structural elements that form the active site cavity are shown as ribbons, and residues of interest are shown as sticks. For each pair of enzymes (GES-1 and GES-7 [A], GES-2 and GES-13 [B], and GES-5 and GES-6 [C]), the Glu104 variant is colored black and the Lys104 variant gray. In all cases, the Glu104Lys substitution caused a movement of Trp105 to the interior of the active site. An estimation of the degree of Trp105 movement can be given by measuring the distance between the Trp105 Cβ atoms of Glu104 and Lys104 variants. The above effect of Lys104 could be explained by its interactions with the helix of the Ω loop that lies beneath. Displacements of the side chain of Glu166 in the case of GES-1 (A) and of the side chain of Asn170 in GES-2 (B) are also apparent.