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. Author manuscript; available in PMC: 2014 May 21.
Published in final edited form as: Biochemistry. 2013 May 7;52(20):10.1021/bi400322e. doi: 10.1021/bi400322e

Figure 1.

Figure 1

A. Structure of E. coli DHFR: adenosine binding domain is shown in pink. Two different structures are superimposed, E:FOL:NADP+ (1RX2),3 with the Met20 loop in the closed configuration (shown in blue) and E:THF:NADP+ (1RX4)3 with the Met20 loop in the occluded configuration (shown in red). The F–G loop is shown in green, and the G–H loop in purple. Folate (from 1RX2) is shown in yellow; NADP+ is in blue for the closed state and red for the occluded state, with the nicotinamide ring in a position out of the active site pocket. B. Enzymatic cycle for DHFR, colored according to the superimposed structures in part A. Top row shows the closed complexes; bottom row, occluded. In addition to the intermediates of the catalytic cycle and analogues, 3J measurements also were obtained for the closed N23PP/S148A E:FOL:NADP+ complex. C. Schematic showing each of the χ1 rotamers (here for isoleucine), with the measured couplings indicated; rotamer populations are calculated based on the measured 3JCγCO and 3JCγN values using Eqs 1–3.