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The enzyme dihydrofolate reductase (DHFR) catalyzes the reduction of 5,6-dihydrofolate to 5,6,7,8-tetrahydrofolate. A movie depicting conformational changes of DHFR during one turnover of substrate has been constructed using six isomorphous crystallographic structures. To re-run the movie, click on the Reload button on your Netscape window.
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Please click here for a KEY to DHFR's mobile structural elements.
The sequence of events in this movie was chosen to correspond to the predominant kinetic pathway of Escherichia coli DHFR under cellular concentrations of substrates and products. The pathway was first determined by Fierke CA; Johnson KA; Benkovic SJ., Construction and evaluation of the kinetic scheme associated with dihydrofolate reductase from Escherichia coli. Biochemistry, 1987 Jun 30, 26(13):4085-92. The kinetic pathway appears below.
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Six isomorphous crystal structures of E. coli DHFR were solved (column 2 of table below), each structure analogous to a complex in the kinetic pathway (column 3 of table below). The largest motions observed correspond to M20 loop movements and subdomain movements (columns 4 & 5). These structures are depicted in the movie above in frames 01, 24, 25, 44, 51 and 56. Other frames were generated using the template forcing algorithm of the program Discover, part of a collection of programs from MSI. For further details, see Sawaya, M. R. & Kraut, J. Loop and Domain Movements in the Mechanism of E. Coli Dihydrofolate Reductase: Crystallographic Evidence. Accepted for publication in Biochemistry.
| Movie Frame | Crystal Structure Analogue | Analogous to | M20 Loop | Subdomain |
| 01 | E*NH | E*NH | closed | open |
| 24 | E*FOL*N+ | E*DHF*NH | closed | closed |
| 25 | E*MTX*NH | E*DHF*NH | closed | closed* |
| 44 | E*ddTHF*ATP-ribose | E*THF*N+ | occluded | open |
| 51 | E*ddTHF | E*THF | occluded | closed |
| 56 | E*ddTHF*NH | E*THF*NH | occluded | open |
The movie, containing 72 frames, was assembled using GIFMerge . Images were constructed with the graphics program SETOR written by Stephen Evans (elmo@nrcbsa.bio.nrc.ca) If you dont have Netscape Version 2.0 or better and the image below is static you may download an upgraded version of Netscape here. An ENLARGED version of the movie may be viewed with SGI's movieplayer software. To view the movie, click on DHFR the MOVIE!. A special thanks goes to Sunny Kim for her help in assembling the movie.
If you have any comments about my movie, please click on my email Michael R. Sawaya (msawaya@ucsd.edu). A screen should pop up (its self explanatory) and there will be buttons for send and cancel. You may also wish to visit my homepage.
