Structural approaches to probing metal interaction with proteins
Graphical abstract
Metallodrug ethacraplatin binding to the detoxifying enzyme glutathione transferase. The intact compound binds first at the enzyme's dimer interface, the compound is then cleaved and the ethacrynic moieties transverse to the substrate-binding site to inhibit the enzyme while the platinum center remains bound to the dimer interface.
Highlights
► Glutathione transferases are involved in the anti-cancer metallodrug resistance. ► Zn binding to insulin-regulated aminopeptidase controls activity and regulation. ► Cu binding to Alzheimer's amyloid precursor protein affects signaling and processing. ► Crystallography and XAS have proved to be complementary in studies of these proteins.
Introduction
Professor Hans Freeman AM FAA made a number of highly important contributions to bioinorganic chemistry, amongst which include setting up the first protein crystallography laboratory in Australia, being a strong advocate and supporter of synchrotron science and its applications in biology and using X-ray crystallography and other biophysical tools, such as X-ray absorption spectroscopy (XAS), to probe the function of blue copper proteins [1].
In this mini-review we highlight recent discoveries at St Vincent's Institute (Melbourne, Australia), one of the oldest protein crystallography centers in Australia [2], on metal interactions with proteins with a particular emphasis on the evident synergism between different biophysical approaches to understanding metallobiology. This review focuses on three biological systems: 1) glutathione S-transferases (GSTs) which normally function by recognizing foreign small molecule toxins in the body and causing them to be eliminated from the cell. Unfortunately, commonly used anti-cancer drugs such as cisplatin are also recognized as toxic and thus GSTs contribute to the resistance of such drugs; 2) insulin-regulated aminopeptidase (IRAP) which appears to be the target for small memory enhancing molecules. This aminopeptidase uses zinc for both catalysis and for regulating its activity; 3) amyloid precursor protein (APP) which appears to play a central role in Alzheimer's disease. Copper ions have been implicated in playing both beneficial and detrimental roles in the disease by binding to different regions of APP.
Section snippets
Copper in Alzheimer's disease
Metals have been implicated in Alzheimer's disease (AD), in part, through their association with the amyloid precursor protein (APP). APP is a large Type I membrane protein that is processed by a group of enzymes known as secretases. APP's large extracellular domain is shed by either α-secretase or β-secretase leaving, respectively, 83 or 99 amino acid C-terminal fragments that are sequentially processed by the integral membrane protein complex called γ-secretase. By cutting APP closer to the
XAS in health and disease
The structural characterization of metal-binding interactions with metalloenzymes using X-ray absorption spectroscopy is well established in the bioinorganic literature and the advantages of using the technique to complement X-ray crystallographic and other information are evident in the examples discussed above. Despite the fact that it is a relatively information-poor technique, the “phase agnostic” nature of XAS means that it is especially useful in identifying situations where other
Concluding remarks
We have described a number of biophysical tools used to characterize metal-binding interactions with proteins including mass spectrometry, bioinformatics, computational modeling, NMR, EPR, X-ray crystallography, XANES and EXAFS. In each case the complementarity of the techniques in exploring a biological problem has been highlighted. Indeed it was shown that a multi-pronged approach was essential to provide a more complete understanding of the biology behind each case study. We also highlighted
Table of abbreviations
- Aβ
peptide associated with Alzheimer's disease
- AD
Alzheimer's disease
- AngIV
angiotensin IV
- APP
amyloid precursor protein
- AT4
angiotensin IV
- CPT
cisplatin
- CuBD
copper binding domain of amyloid precursor protein
- EA
ethacrynic acid
- EACPT
ethacraplatin
- EXAFS
extended X-ray absorption fine structure spectroscopy
- GFD
growth factor domain of amyloid precursor protein
- GSH
glutathione
- GST
glutathione S-transferase
- GSTP1-1
pi class isoform of GST
- ICP-MS
inductively coupled plasma mass spectrometry
- IRAP
insulin regulated aminopeptidase
Acknowledgments
We thank all present and past staff of BSBL and our collaborators for all their contributions toward the studies highlighted in this review. Infrastructure support from the National Health and Medical Research Council Independent Research Institutes Infrastructure Support Scheme and the Victorian State Government Operational Infrastructure Support Program is gratefully acknowledged. L.J.P. was supported by a National Health and Medical Research Council of Australia (NHMRC) Dora Lush Scholarship
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Cited by (0)
- 1
Present address: RIKEN Systems and Structural Biology Center (SSBC) 1-7-22, Suehiro-cho, Tsurumi-ku, Yokohama City, Kanagawa, 230-0045, Japan.
- 2
These authors made equal contributions.
- 3
Co-senior authors.