Fig. 8: Proposed nucleotide addition cycle.
From: Structural basis of deoxynucleotide addition by HIV-1 RT during reverse transcription
We observed five unique intermediate states (R-1, R-2, T8sec, P2min, P6min) that suggest a possible cycle for nucleotide addition. See the text for a detailed description. (1) dNTP-free (dash ellipse) RT-T/P binary complex (red). + symbol indicates positive charges. (2) In state R-1 (yellow), a dNTP binds in the active site pocket and recruits site B metal. (3) Binding of dNTP triggers active site closure. (4) dNTP in the active site pocket attracts site A* metal (state R-2, blue). (5) Coordination of site A* metal elicits a pre-catalytic conformation (state T8sec, gray). Curved lines around site A* metal indicate that its position is mobile. (6) Concurrence of the primer 3′-OH, the α-phosphate, and site A* metal (state P2min and P6min, teal) trigger phosphodiester bond formation (dash circle) and PPi release. (7) Upon translocation (black arrows), the β3-β4 loop returns to its open conformation (teal/red arrow) to restart the cycle.
