5 4 , ▁Asp 1 8 4 ▁among ▁others ▁in ▁addition ▁to ▁various ▁non con ser ved ▁resid ues ▁such ▁as ▁Le u 7 4 ▁and ▁G ln 8 4 . ▁Most ▁of ▁the ▁conser ved ▁resid ues ▁in ▁PK A ▁interact ▁with ▁ATP ▁whereas ▁interactions ▁of ▁ATP ▁with ▁the ▁non con ser ved ▁resid ues ▁do ▁not ▁occur . ▁ ▁Six ▁ordered ▁water ▁mole cules ▁also ▁play ▁critical ▁roles ▁in ▁bal an ol ▁binding ▁to ▁PK A . ▁Several ▁PK A ▁resid ues ▁such ▁as ▁Le u 4 9 ▁and ▁T yr 3 3 0 ▁hydro gen ▁bond ▁with ▁conser ved ▁water ▁mole cules . ▁These ▁water ▁mole cules ▁also ▁medi ate ▁interactions ▁between ▁bal an ol ▁and ▁the ▁resid ues ▁of ▁the ▁catal yt ic ▁c left ▁of ▁PK A ; ▁for ▁example , ▁two ▁water ▁mole cules ▁form ▁a ▁bridge ▁to ▁allow ▁bal an ol ' s ▁N 1 ’ ▁atom ▁to ▁interact ▁with ▁the ▁hydro x yl ▁group ▁of ▁T yr 3 3 0 . ▁ ▁However , ▁the ▁tight ▁interaction ▁of ▁bal an ol ▁with ▁the ▁ATP - binding ▁site ▁that ▁leads ▁to ▁bal an ol ' s ▁pot ency ▁as ▁an ▁in hib itor ▁is ▁not ▁due ▁to ▁hydro gen ▁bond ing ▁but ▁rather ▁because ▁of ▁the ▁pre domin ant ▁non pol ar ▁interactions ▁the ▁mole c ule ▁makes . ▁For ▁instance , ▁bal an ol ' s ▁ben z oph en one ▁rings ▁are ▁position ed ▁beside ▁the ▁g ly c ine - rich ▁loop ▁and