TABLE 3.

Search and validation criteria for the identification of HQD candidates

Characteristic(s)a	Detail/function	Reference(s)
[H-x(2)-W]97-100	Simplified nucleophilic elbow motif; motif 3
[HFP-x(4)-P]246-253	Motif 9, including triad’s histidine
αCap1-αCap4	Cap domain formation; contributes to substrate binding, shields oxidation reaction from surrounding	26, 33, 48
D121	Triad acidic residue is an Asp positioned between β6 and αCap1	26, 33
[W/L]31, H97, [I/V]187	Oxyanion hole formation and contribution to substrate binding site	26, 33
[F/L]131, [M/L/V/I]135, [F/L]151, W155, W180	Contribute to the hydrophobic cavity for the quinolone substrate; alternative hydrophobic residues might be permitted	26, 33
M172	Optional; potentially blocks alkyl-tail tunnel; indicator that short-chained substrates are preferred	33
A96	Optional; replaces triad nucleophile; indicator for high kcat	33

^aNumbering of amino acids according to AqdC sequence.