Eric Oldfield (academic)

In the 1970s and 1980s Oldfield developed ways to investigate lipid and membrane structure including the use of 2H nuclear magnetic resonance (NMR) spectroscopy of labelled compounds.[6][7] This method enabled the determination of the static and dynamic structures of lipids, and how they interact with proteins and sterol molecules such as cholesterol.[8] In addition, he developed 1H and 13C magic-angle sample-spinning methods to investigate lipid membranes without the need for isotopic labeling. The magic-angle technique was not thought to be applicable to 1H NMR (due to strong dipolar interactions), but he showed that due to fast axial diffusion, these interactions were scaled and that remarkably high-resolution spectra could be obtained.[9]

In the early 1970s, while working with Adam Allerhand, Oldfield reported the first high-resolution 13C NMR spectra of proteins—lysozyme, myoglobin and cytochrome c—in which numerous single carbon atom sites could be resolved and assigned.[10][11] The origins of the chemical shift non-equivalencies observed due to folding remained unexplained until 1993 when he showed that 13C and 15N chemical shifts in proteins could be well predicted by using quantum chemical methods. He reasoned that since the chemical shift is essentially a local phenomenon, it might be possible to compute chemical shifts just by using small peptide fragments and a “locally dense” basis set, and this turned out to be correct.[12] His early work also led to the demonstration that computed chemical shift tensors could be used in protein structure refinement.[13] Moreover, he showed that the chemical shifts of non-native species in proteins such as 19F nuclei, could be also be computed, and were due to electric field effects.[14]

Followed by the observation that chemical shifts in proteins could be computed by using quantum chemical methods, Oldfield began a series of investigations of other spectroscopic properties[15] including Mössbauer isomer shifts[16] and quadrupole splittings,[17] hyperfine shifts in metalloproteins,[18] spin-spin couplings,[19] and electric field gradients, as well as the effects of hydrogen bonding on chemical shifts.[20]

Oldfield began to investigate structures of a variety of inorganic solids in the 1980s. He showed that high-resolution spectra of quadrupolar nuclei (such as 17O, 23Na) could be obtained by using variable-angle sample-spinning,[21] spin echo,[22] as well as spectral deconvolution methods.[23] In his collaborative research with R. James Kirkpatrick, he investigated the 29Si magic-angle sample-spinning NMR spectra of a wide range of natural and synthetic silicates,[24] showing that both Si-O bond length-chemical shift and bond strength-chemical shift relationships were useful tools for investigating the structures of crystalline silicates and, more importantly, silicate glasses, clays, and zeolites that cannot be examined by single crystal X-ray or neutron diffraction methods. He also worked on investigating Pt/Ru direct methanol oxidation fuel cell catalysts using 13C and 195Pt NMR, in collaboration with A. Wieckowksi, which clarified the mechanism of enhanced CO tolerance in Pt/Ru versus pure Pt catalysts.[25]

In 1999, Oldfield shifted his research to more biomedical applications. Working in collaboration with Julio Urbina and Roberto Docampo, his group found, using 31P NMR spectroscopy, that the parasitic protozoan Trypanosoma cruzi, the causative agent of Chagas disease, contained very high levels of diphosphate, and that diphosphate analogs, bisphosphonates used clinically to treat bone resorption diseases, killed these parasites.[26] as well as others.[27] He also discovered that the bisphosphonate pamidronate cured mice of leishmaniasis[28] and proposed that farnesyl diphosphate synthase (FPPS) can be used as the target of bisphosphonate drugs[29]

Oldfield then discovered another compound that killed T. cruzi, the antiarrhythmic drug amiodarone, and that it acted synergistically with the azole drug posaconazole.[30] He then began to investigate antibacterial agents. The human pathogen Staphylococcus aureus contains a gold-colored virulence factor called staphyloxanthin that protects the bacterium from killing by reactive oxygen species.[31] Recognizing that the biosynthesis of the carotenoid pigment had similarities to the first steps in cholesterol biosynthesis, he synthesized a range of cholesterol biosynthesis inhibitors and tested them in S. aureus and in mice models of infection finding potent activity against the protein target dehydrosqualene synthase, the bacterium, and in a mice model of infection.[32] His group also showed that some drugs and drug leads that target tuberculosis bacteria function as protonophore uncouplers and in some cases they can also target isoprenoid biosynthesis, leading to potent multi-target inhibition.[33]

In 2012, Oldfield's group synthesized lipophilic analogs of the clinical bisphosphonate drugs zoledronate and risedronate, to prevent unwanted binding to bone mineral, and found they had potent anti-malarial activity.[34] Additionally, they had potent activity in a combination therapy with rapamycin in tumor cells and in mice, by targeting protein prenylation[35] with inhibition of protein prenylation also leading to activity as vaccine adjuvants.[36] Mechanistically, FPPS inhibition affects cell signaling, but it also leads to accumulation of isopentenyl diphosphate and dimethylallyl diphosphate, compounds that activate γδT cells by binding to butyrophilins in target cells[37] and this T cell activation led to tumor cell killing.[38] His group also showed that some clinically used bisphosphonate drugs are converted to analogs of adenosine triphosphate that function by inhibiting cell signaling pathways.[39]

Oldfield and his collaborators have reported the structures and mechanisms of action of many proteins involved in isoprenoid biosynthesis, focusing on the modular structures found.[40] They successfully predicted the αβγ tri-domain found in diterpene cyclases.[41] Furthermore, they used electron paramagnetic resonance and X-ray crystallography to develop the organometallic mechanism of action of the unusual 4Fe-4S proteins IspG and IspH involved in the early stages of isoprenoid biosynthesis,[42] and also used X-ray methods for providing mechanisms of action for the terpene cyclases.[43]