<p>(<b>A</b>) Homology modeling derived structural models showing docking of wild-type PknQ (stick diagram) with the wild-type FHA domain variable loop region of MupFHA (green ribbon diagram). Phosphate group (orange) has been added to Ser<sup>170</sup> and Thr<sup>174</sup> of PknQ and the phosphorylated residues have been renamed as Sep170 and Tpo174, respectively. The red encircled region of interaction has been enlarged in (<b>B</b>). The residues Arg<sup>41</sup>, Arg<sup>53</sup>, Ser<sup>55</sup>, Arg<sup>56</sup> and Ser<sup>75</sup> of MupFHA show stable interactions with the PknQ activation loop and form H-bonds with the negatively charged pSer<sup>170</sup> (Sep170) and pThr<sup>174</sup> (Tpo174). (<b>C</b>) Enlarged region of interaction between PknQ-pThr<sup>174</sup> and MupFHA. Canonical interaction of pThr<sup>174</sup> is observed showing H-bonds with Arg<sup>53</sup>, Ser<sup>55</sup> and Ser<sup>75</sup> of MupFHA (see text). (<b>D</b>) Enlarged region of interaction between PknQ-pSer<sup>170</sup> and MupFHA. PknQ-pSer<sup>170</sup> is shown to be anchored by the residues Arg<sup>41</sup> and Arg<sup>56</sup> of MupFHA. (<b>E</b>) Region of interaction between PknQ-pThr<sup>174</sup> and MupFHA<sup>S55A</sup> (in red stick). (<b>F</b>) Region of interaction between PknQ-pSer<sup>170</sup> and MupFHA<sup>R41A</sup> (in red stick). Both (E) and (F) show the loss of H-bond network and thus destabilized interaction between PknQ and MupFHA.</p