Imaging metals within cells: Identifying the proteins that bind

September 10, 2012, Argonne National Laboratory
Imaging metals within cells: Identifying the proteins that bind
X-ray image of a 2-D native electrophoretic separation. The sulfur content, often part of cysteine and methionine residues in proteins, is shown in red. The zinc content is shown in green. By sampling protein that co-localizes with the metal for mass spectrometry, researchers can identify the proteins that bind them.

(—Metals such as copper, zinc, and iron are important nutrients to all life. The special properties of these elements that make them so useful in technologies including batteries and catalysts – for example, having multiple stable oxidations states under ambient conditions – also make them useful to living organisms.

With over a third of all proteins thought to bind metals, knowing which metals are bound and how that binding changes in response to the environment could have big implications.

For instance, the biological of metals is involved in many diseases, including Lou Gehrig's disease, Wilson and Menkes disease, and possibly even Alzheimer's disease.

Metals are also an environmental toxin, such as the hexavalent chromium featured in the movie Erin Brockovich, and they are used in drugs, like the platinum in that treats .

Developing an approach for making determinations about the relationship of metals and proteins is complex because the experimental methods that are routinely used to identify proteins, for example denaturing gel electrophoresis, can also remove metals that might be bound to them.

Imaging metals within cells: Identifying the proteins that bind
Lydia Finney, Carol Giometti, and Stefan Vogt (all from Argonne) with the XRF instrument in the XSD 8-BM-B research enclosure at the APS.

Scientists working at the Department of Energy Office of Science's Advanced Photon Source (APS) at Argonne have made great strides in imaging metals within cells. Using the x-ray imaging capabilities afforded by the APS, researchers have seen, often for the first time, where the metals reside inside cells and tissues. These capabilities have allowed researchers to see how the elemental content of bacteria change upon adhesion, fluxes of zinc in upon fertilization, and changes in the locations where copper is stored in a cell during the growth of blood vessels.

But many of the images that have been acquired led to new questions: Are these metals required for the activity of proteins? Which proteins are binding with which metals inside the cell?

Now, a team of researchers from the Worcester Polytechnic Institute and Argonne carrying out research at the APS have developed a new experimental approach that not only detects and distinguishes metals in proteins, but also characterizes the proteins that bind the metals, without removing them. This work, which was featured on the cover of the journal Metallomics, utilized x-ray fluorescence imaging (XRF) at X-ray Science Division (XSD) beamline 8-BM-B of the APS.

Employing modified native two-dimensional gel electrophoresis, the researchers were able to separate proteins from the organisms S. oneidensis, a bacterium that can reduce poisonous heavy metal and can live in both environments with or without oxygen, and P. aeruginosa, a common bacterium that can cause disease in animals, including humans, and that is found in soil, water, skin flora, and most man-made environments throughout the world. Then, using XRF, the team quantitatively measured the amount of sulfur, iron, and zinc at every point of the two-dimensional (2-D) separation, pinpointed the location of proteins that had metals bound to them, and determined the identity of these proteins utilizing mass spectrometry.

The approach enabled the research team to identify a novel protein (PA5217) as a zinc-binding protein in P. aeruginosa.

Their finding highlights how this method not only determines changes in occupancy, but also identifies the associated .

Now that this new technique is developed, questions raised by images of the metals in cells can be studied further.

Native 2-D gel electrophoresis separation is accessible to most laboratories, and resources for 2-D XRF imaging are available at the APS.

This development will help researchers begin to identify which of the one-third of proteins that are thought to bind metals actually do, and what roles they play in life.

Explore further: Heavy metals boost immunity

More information: Daniel Raimunda, Tripti Khare, Carol Giometti, Stefan Vogt, José M. Argüello, and Lydia Finney, "Identifying metalloproteins through X-ray fluorescence mapping and mass spectrometry," Metallomics 4, 921 (2012). DOI:10.1039/c2mt20095c

Related Stories

Heavy metals boost immunity

September 21, 2011

A new natural defense mechanism against infections has been evidenced by an international team led by researchers from CNRS, Inserm, the Institut Pasteur and the Universite Paul Sabatier – Toulouse III. Zinc, a heavy ...

Decrease in Metals Contamination Seen Over the Past 30 Years

June 15, 2006

The U.S. report card on metals contamination in sediment is showing marked improvement. A new study has analysed the past three decades of environmental legislation and regulation, changing demographics and land-use practices ...

New method revolutionizes study of metal-containing proteins

July 18, 2010

Metals and proteins are crucial partners in keeping organisms healthy and stable. And yet the extent to which this molecular metalloprotein team works at the cellular level is not known because the numbers, amounts and types ...

Proteins prove their metal

July 7, 2010

( -- The word 'metal' conjures up images of machines and heavy industry but metals are also intimately involved in the biological processes that regulate our bodies and underpin new energy technologies.

Recommended for you

Programming DNA to deliver cancer drugs

March 19, 2018

DNA has an important job—it tells your cells which proteins to make. Now, a research team at the University of Delaware has developed technology to program strands of DNA into switches that turn proteins on and off.

Modified biomaterials self-assemble on temperature cues

March 19, 2018

Biomedical engineers from Duke University have demonstrated a new approach to making self-assembled biomaterials that relies on protein modifications and temperature. The hybrid approach allows researchers to control self-assembly ...

Identifying 'designer' drugs taken by overdose patients

March 19, 2018

Drug overdoses are taking a huge toll on public health, with potent synthetic drugs posing a particular threat. Medical professionals are scrambling to meet the growing demand for emergency room treatment, but they're hampered ...

The Swiss army knife of smoke screens

March 18, 2018

Setting off smoke bombs is more than good fun on the Fourth of July. The military uses smoke grenades in dangerous situations to provide cover for people and tanks on the move. But the smoke arms race is on. Increasingly, ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.