3.2. Overall structure
The unit cell parameters for the orthorhombic crystal structure
of the ConM complexed with IAA were as follows: a ¼ 67.1 A,
b ¼ 70.7 A and c ¼ 97.7 A, and the Matthews coefficient was
2.32 A3 Da1, indicating the presence of a monomer in the asymmetric
unit. The final refinement statistics and structure analysis
are shown in Table 1.
The refined structure of ConMeIAA complex at a 2.15 A is a
tetramer in biological assemble consisting of two “canonical” dimers
linked by salt bridges between b strands and by IAAeprotein
interactions (Fig. 2). The atomic coordinates for the structure were
deposited in the Protein Data Bank (PDB) with the access code
3SNM.
The IAA strong (FoeFc map e 3 s) electron density was found in
the polar central cavity of the ConM tetramer structure (Fig. 3A).
The IAA molecule was positioned in the electron density map and
refined. The omit map confirmed the presence of the ligand. Upon
inspecting the structure, an electron density was observed near the
carbohydrate binding site. This density could be due to a free indole
group, the oxidation product of IAA photodecomposition. The
indolewas positioned in the site and fully embedded in the electron
density map (Fig. 3B). The overall interactions are shown in Table 2.