U-shaped channel network formed in presence of βK in the secondary channel. The U-shaped channel connects primary funnel access with the catalytic centre (large unfilled arrow), the secondary channel (thin arrow) and the dimer interface (large dotted arrows). In presence of βK a tunnel is formed between Cys112-bound anthranilate (CSJ) and the central cavity (dashed thin arrow) potentially used for water supply (needed for catalysis) from the central cavity to the oxyanion site close to P88′. βK is shown as green ball and sticks, whereas residues shown to interact with βK (CSJ, T195, F218, R145, D87′, P88′) as cyan sticks. For clarity the domains are labelled with their abbreviations. The solvent accessible surface is color-coded as follows: blue – positive electrostatic potential (+25 kcal/mol); red – negative electrostatic potential (−25 kcal/mol), white – neutral.