The effect of hydration on the dynamics of trimethoprim bound to dihydrofolate reductase. A deuterium NMR study

To determine the effect of hydration on the dynamics of a protein complex, we used deuterium nuclear magnetic resonance (NMR) techniques to examine a trimethoprim (TMP)/E. coli dihydrofolate reductase (DHFR) complex in its lyophilized, partially hydrated, polycrystalline, and ammonium sulfate-precipitated states. The results indicate that TMP is rigid in the lyophilized powder state. The dynamic behavior could be restored by partial rehydration. At 30 wt% hydration the deuterium spectrum of the partially hydrated sample was indistinguishable from that of the polycrystalline and ammonium sulfate-precipitated samples, suggesting that the structure of the protein/TMP complex is similar in the three physical states. Furthermore, we found that the para- and meta-methoxyl groups have very different dynamical behavior.