# Douglas C. Rees
**Douglas C. Rees** (D.C. Rees) is an American structural biochemist, the Roscoe Gilkey Dickinson Professor of Chemistry at the [California Institute of Technology](https://www.edgepedia.org/california-institute-of-technology), whose laboratory determined the first crystal structure of the nitrogenase molybdenum–iron protein and has defined the structural biology of complex metalloproteins and ATP-driven membrane proteins.[1](https://directory.caltech.edu/personnel/dcrees) • [2](https://cce.caltech.edu/faculty/douglas-c-doug-rees) His group's structures of the nitrogenase FeMo-cofactor and the pterin-containing molybdenum cofactor defined the structural biology of molybdenum and tungsten, the only second- and third-row transition metals used biologically.[2](https://cce.caltech.edu/faculty/douglas-c-doug-rees) He was an Investigator of the [Howard Hughes Medical Institute](https://www.edgepedia.org/howard-hughes-medical-institute) from 1997 to 2025 and is now listed as investigator emeritus.[3](https://hhmi.org/scientists/douglas-c-rees)
| Fact | Detail |
|---|---|
| Field | Structural biochemistry and structural bioenergetics[4](https://www.nasonline.org/directory-entry/douglas-c-rees-x0j4gc/) |
| Position | Roscoe Gilkey Dickinson Professor of Chemistry, Caltech (since 2004)[1](https://directory.caltech.edu/personnel/dcrees) |
| Training | B.S. Yale 1974 (with Carolyn W. Slayman); Ph.D. Harvard 1980 (with William Lipscomb); postdoc, University of Minnesota, with James B. Howard[5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) |
| Signature work | First crystal structure of the nitrogenase MoFe-protein (Nature, 1992)[6](https://www.caltech.edu/about/news/figuring-out-how-we-get-nitrogen-we-need-44125); ["Crystallographic structure and functional implications of the nitrogenase molybdenum–iron protein from Azotobacter vinelandii"](https://doi.org/10.1038/360553a0), *Nature*, 1992 |
| Honors | National Academy of Sciences (elected 2000); American Academy of Arts and Sciences; HHMI Investigator 1997–2025[4](https://www.nasonline.org/directory-entry/douglas-c-rees-x0j4gc/) • [5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) • [1](https://directory.caltech.edu/personnel/dcrees) |
| Recent work | Turnover-state nitrogenase structures, including alkaline-turnover states (Nature Communications, 2024)[7](https://orcid.org/0000-0003-4073-1185) |
## Education and career
Rees completed a B.S. in Molecular Biophysics and [Biochemistry](https://www.edgepedia.org/biochemistry) at Yale in 1974, studying cytochrome in [Neurospora](https://www.edgepedia.org/neurospora) with Carolyn W. Slayman, an early exposure to electron transfer in microbes.[5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) He received a Ph.D. in [Biophysics](https://www.edgepedia.org/biophysics) from Harvard in 1980, determining crystal structures of carboxypeptidase A with William Lipscomb.[5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) He has said he discovered protein structure through a fortunate first-year Harvard graduate course on protein structure and function.[8](https://heritageproject.caltech.edu/interviews/douglas-c-rees)
During a two-year postdoctoral appointment at the [University of Minnesota](https://www.edgepedia.org/university-of-minnesota) with James B. Howard, he produced the first crystals of the nitrogenase iron protein from *Azotobacter vinelandii*, the starting point for a collaboration with Howard that lasted 35 years.[5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) He joined the faculty of the Department of Chemistry and Biochemistry at UCLA in 1982 and moved to Caltech in 1989.[5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) The Caltech directory records him as Professor from 1989 to 2004 and Roscoe Gilkey Dickinson Professor from 2004.[1](https://directory.caltech.edu/personnel/dcrees) He was appointed an HHMI Investigator in 1997, and he has said HHMI funding transformed his group's ability to work on membrane proteins, a field then considered too risky for NIH support.[1](https://directory.caltech.edu/personnel/dcrees) • [8](https://heritageproject.caltech.edu/interviews/douglas-c-rees)
## Research
The Rees group works on the structures and mechanisms of complex metalloproteins and integral membrane proteins, particularly those involved in ATP-dependent energy transduction.[2](https://cce.caltech.edu/faculty/douglas-c-doug-rees) His NAS self-description places the work in structural bioenergetics: the molecular basis of energy transduction in photosynthesis, respiration, and mechanosensation, approached through structures of the photosynthetic reaction center, fumarate reductase, and a gated mechanosensitive channel.[4](https://www.nasonline.org/directory-entry/douglas-c-rees-x0j4gc/)
The membrane-protein side of the program includes ATP-binding cassette (ABC) transporters, which use ATP binding and hydrolysis to move ligands across membranes, and prokaryotic mechanosensitive channels of large (MscL) and small (MscS) conductance.[2](https://cce.caltech.edu/faculty/douglas-c-doug-rees) ABC transporters matter beyond basic biology because a major class of drug efflux pumps belongs to this family and can pump therapeutics out of cells, a mechanism tumor cells exploit.[8](https://heritageproject.caltech.edu/interviews/douglas-c-rees) Systems of current interest are ABC transporters mediating nutrient translocation and the molecular mechanism of nitrogenase.[2](https://cce.caltech.edu/faculty/douglas-c-doug-rees)
## Representative work
The laboratory's 1992 Nature paper, "Crystallographic structure and functional implications of the nitrogenase molybdenum–iron protein from *Azotobacter vinelandii*", reported the first structure of the MoFe-protein, described as a milestone revealing an unprecedented catalytic center.[6](https://www.caltech.edu/about/news/figuring-out-how-we-get-nitrogen-we-need-44125) • [9](https://www.mdpi.com/1420-3049/28/24/7952) The FeMoco it visualized is the composition [Mo:7Fe:9S:C], described as the largest known metal cluster, catalyzing the six-electron reduction of dinitrogen to ammonium.[10](https://www.nature.com/articles/ncomms10902) Later work refined the model: at 2.0 Å resolution an originally unassigned µ2-bridging ligand was identified as a third bridging sulfide (S5A), and in 2011 the central light atom was identified as an interstitial carbide through a combination of HERFD-XAS, ESEEM, and high-resolution crystallography.[9](https://www.mdpi.com/1420-3049/28/24/7952)
The second anchor paper, "Structure of ADP·AlF4−-stabilized nitrogenase complex and its implications for signal transduction" (Nature, 1997; [doi:10.1038/387370a0](https://doi.org/10.1038/387370a0)), captured the two-component enzyme with a transition-state mimic of ATP, linking the nucleotide state of the Fe-protein to conformational signaling between the proteins.[11](https://feeds.library.caltech.edu/people/Rees-D-C/article.html) Nitrogenase comprises the MoFe-protein, bearing the FeMo-cofactor active site, and the Fe-protein that couples ATP hydrolysis to electron transfer for the ATP-dependent reduction of dinitrogen to ammonia under ambient conditions.[12](https://royalsocietypublishing.org/rsta/article/363/1829/971/52051/Structural-basis-of-biological-nitrogen-fixation) Structures at about one Ångstrom resolution later revealed a hexa-coordinate central carbon and a sulfur atom capable of reversible displacement, and a structure reported in Science showed carbon monoxide bound to the FeMo-cofactor in place of a bridging sulfur between two iron atoms; removing the CO allows the sulfur to reattach and reactivate the cofactor.[5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) • [6](https://www.caltech.edu/about/news/figuring-out-how-we-get-nitrogen-we-need-44125)
## Honors and professional roles
Rees was elected to the National Academy of Sciences in 2000 and is a member of the American Academy of Arts and Sciences.[4](https://www.nasonline.org/directory-entry/douglas-c-rees-x0j4gc/) • [5](https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html) Beyond research, the Caltech directory records service as Executive Officer in 2002–06 and 2007–15, Dean of Graduate Studies from 2015 to 2020, and Executive Officer for Biochemistry in 2025–26.[1](https://directory.caltech.edu/personnel/dcrees)
## Recent work (2024–2026)
A 2024 conference abstract, "Nitrogenase: Beyond the Resting State," reported that ligand binding under turnover conditions can be accompanied by reversible displacement and rearrangement of sulfurs in the catalytic FeMo-cofactor.[13](https://doi.org/10.1016/j.jbc.2024.106229) A 2024 [Nature Communications](https://www.edgepedia.org/nature-communications) paper examined the structural evolution of nitrogenase states under alkaline turnover.[7](https://orcid.org/0000-0003-4073-1185) Rees gave a talk of the same title at UC Santa Barbara on April 23, 2025, described there as Dickinson Professor and HHMI Investigator until August 2025; his group uses [X-ray crystallography](https://www.edgepedia.org/x-ray-crystallography) and electron microscopy.[15](https://bioengineering.ucsb.edu/events/all/2025/douglas-rees-phd-professor-chemistry-california-institute-technology-nitrogenase) He is teaching Ch/Bi 110, the introductory biochemistry course, in the 2025–26 academic year.[2](https://cce.caltech.edu/faculty/douglas-c-doug-rees) His ORCID record also lists a perspective titled "Biological nitrogen fixation in theory, practice, and reality: a perspective on the molybdenum nitrogenase system."
## References
1. Douglas C. (Doug) Rees – Caltech Directory. https://directory.caltech.edu/personnel/dcrees
2. Douglas C. (Doug) Rees – Caltech Division of Chemistry and Chemical Engineering. https://cce.caltech.edu/faculty/douglas-c-doug-rees
3. Douglas C. Rees, PhD | HHMI Investigator Emeriti Profile | 1997-2025. https://hhmi.org/scientists/douglas-c-rees
4. Douglas C. Rees – National Academy of Sciences member directory. https://www.nasonline.org/directory-entry/douglas-c-rees-x0j4gc/
5. Information about Hageman lecturer Douglas Rees – Kansas State University. https://www.k-state.edu/bmb/about/seminars/hageman/2016-Rees.html
6. Figuring Out How We Get the Nitrogen We Need – Caltech News. https://www.caltech.edu/about/news/figuring-out-how-we-get-nitrogen-we-need-44125
7. Douglas Rees (0000-0003-4073-1185) – ORCID. https://orcid.org/0000-0003-4073-1185
8. Douglas C. Rees – Caltech Heritage Project oral history (September 17, 2021). https://heritageproject.caltech.edu/interviews/douglas-c-rees
9. Nitrogenase beyond the Resting State: A Structural Perspective (Molecules, 2023). https://www.mdpi.com/1420-3049/28/24/7952
10. Nitrogenase FeMoco investigated by spatially resolved anomalous dispersion refinement (Nature Communications, 2016). https://www.nature.com/articles/ncomms10902
11. Caltech Library Feeds – Rees-D-C article list. https://feeds.library.caltech.edu/people/Rees-D-C/article.html
12. Structural basis of biological nitrogen fixation (Philosophical Transactions of the Royal Society A, 2005). https://royalsocietypublishing.org/rsta/article/363/1829/971/52051/Structural-basis-of-biological-nitrogen-fixation
13. Abstract 2246 Nitrogenase: Beyond the Resting State (Journal of Biological Chemistry, 2024). https://doi.org/10.1016/j.jbc.2024.106229
14. Structures of the nitrogenase complex prepared under catalytic turnover conditions (Science, 2022). https://www.science.org/doi/10.1126/science.abq7641
15. Douglas Rees seminar at UCSB, April 23, 2025. https://bioengineering.ucsb.edu/events/all/2025/douglas-rees-phd-professor-chemistry-california-institute-technology-nitrogenase
16. Structural Enzymology of Nitrogenase Enzymes (Chemical Reviews, 2020). https://pubs.acs.org/doi/abs/10.1021/acs.chemrev.0c00067
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*Topic: Encyclopedia › Life and health › Life and health scientists › Life scientists › Researchers in structural biology, biochemistry, and biophysics › Membrane proteins and ion channels › Membrane transport and biochemistry researchers*
*Initially written Sep 20, 2026 · Reviewed: Sep 25, 2026 · Edited: Sep 25, 2026; Oct 11, 2026 · Last review: Sep 25, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license