Kinase phosphoryl transfer (hexokinase) template

Hexokinase: an Asp side chain removes the proton of the glucose C6–OH as it attacks the γ-phosphorus opposite the β,γ-bridging oxygen (in-line, inversion at P), and ADP leaves; Mg²⁺ bound to the β- and γ-phosphates shields their charge. In ATP hydrolysis water is the nucleophile.

Mechanism step by step

In-line attack on the γ-phosphorus of MgATP²⁻: glucose 6-OH becomes glucose 6-phosphate; water does the same in ATP hydrolysis

1. Phosphoryl transfer – Asp (base) takes the 6-OH proton; O6 attacks Pγ in line with the leaving β,γ-bridge oxygen
2. ATP hydrolysis – The same in-line attack with water as the nucleophile (ATPases, myosin)

Key points

• The true substrate is MgATP²⁻: Mg²⁺ on the β- and γ-phosphates shields the negative charge so the nucleophile can approach Pγ.
• In-line attack goes through a trigonal-bipyramidal transition state and inverts the configuration at P (shown with chiral [¹⁶O,¹⁷O,¹⁸O]-phosphoryl groups).
• Hexokinase closes around glucose (induced fit, Koshland), which shuts water out of the site so ATP is not simply hydrolysed.
• ATP hydrolysis: ΔG°′ ≈ −30.5 kJ/mol; in cells ΔG is about −50 to −65 kJ/mol because [ATP]/[ADP][Pᵢ] is held far from equilibrium.

Drawn with 153 atoms, 9 arrows, 6 shapes – every one editable in MolDraw.

Sources

• Nelson & Cox, Lehninger Principles of Biochemistry, 8th ed., 2021, ch. 14 Textbook
• Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019, ch. 9 Textbook