In the x-ray structure 1YHZ the CS molecule is close to and appears to ring stack with Tryptophan 574. The structure is a monomer unit of the dimer however, and the adjacent monomer containing the rest of the herbicide and catalytic sites are not in it. The size of the entry point has to be modeled in, in this case by joining 2 AHAS x-ray determined monomers into a dimer and then adding the CS molecule and x-ray coordinates. The complete tetramer structure 6U9H (and 6VZ8), which does not have a Chlorsulfuron molecule in it, has a wide entry to the tunnel. P197