[Editors] MIT sensor opens up study of crucial molecule

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT sensor opens up study of crucial molecule
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For Immediate Release
THURSDAY, JUNE 1, 2006
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

--PHOTO, IMAGE AVAILABLE--

CAMBRIDGE, Mass.--MIT scientists have discovered a way to monitor a 
crucial molecule as it goes about its business within living cells.

The molecule, nitric oxide (NO), plays critical roles in the human 
body - from the destruction of invading microorganisms to the 
relaying of neural signals.

But catching NO at work has long eluded scientists because it often 
exists in minute concentrations and for only short periods of time. 
Now, MIT chemists have developed a bright fluorescent sensor that, in 
conjunction with microscopy, captures and illuminates NO in living, 
functioning cells.

The work, reported May 28 in the online issue of Nature Chemical 
Biology, will aid scientists' understanding of how and when NO 
operates.

Stephen J. Lippard, the Arthur Amos Noyes Professor of Chemistry at 
MIT, developed the sensor with an eye toward understanding the role 
of NO in neural activity. But this work has broad biological 
applications since NO is produced throughout the body. "Our goal is 
to detect its formation in spatio-temporal terms, to see where and 
when it is produced in a cell, and in which collections of cells, and 
to connect its production with underlying chemical signaling events," 
Lippard said.

Until the 1990s, scientists mainly knew NO as a product of lightning 
and the combustion engine - and as an ingredient in smog. A simple 
molecule consisting of one nitrogen and one oxygen atom, it contains 
an unpaired electron that makes it highly reactive and destructive.

"Nobody thought it would be tolerated by a cell, much less used for 
biological purposes," Lippard said.

Then came the stunning discovery that the peculiar blood vessel 
relaxer Endothelial Derived Relaxation Factor, identified in the 
1980s, was actually NO. NO was then unmasked in macrophages (white 
blood cells), tumors, bones and neurons.

In sweat and saliva it has antibacterial properties; in Viagra, 
rejuvenating effects. Paradoxically, NO often has contradictory 
behaviors. At some levels, it lowers high blood pressure, destroys 
invading microorganisms and tumor cells, maintains bone mass and 
relays neural signals. At other levels, it causes septic shock and 
promotes tumors, arthritis and nerve death.

These puzzles make understanding how and when NO operates in cells 
all the more relevant, and that requires a better means of monitoring 
it as cells go about their normal business. But existing assays have 
either been too invasive or measured NO only indirectly.

Lippard, together with graduate student Mi Hee Lim, the first author 
of the study, and postdoctoral researcher Dong Xu, produced a novel 
NO sensor by attaching a derivative of the widely used cellular 
imaging agent, fluorescein, to a copper atom. The resulting complex 
does not fluoresce until the fluorescein, in modified form, is 
released - which only happens in the presence of NO.

The sensor works in real time, in the aqueous, neutral pH conditions 
of tissues, and at the tiny nanomolar-concentrations of NO found in 
living cells.

How exclusive and selective is the NO detector? To find out, Lim and 
Xu made a mix of banana-shaped neuroblastomas and M&M-shaped 
macrophages, which each require different triggers to synthesize NO 
from a particular amino acid. When they triggered NO production in 
just the neuroblastomas, they could literally see that the sensor had 
selectively detected only those cells.

"That delighted me the most because we want to detect one cell type 
selectively in a heterogeneous population of cells," Lippard said.

Lippard plans to use this NO sensor to learn about the role of this 
elusive molecule in neurobiology. In the nervous system, a neuron 
releases NO at the synapse after receiving a signal from another 
neuron. NO then diffuses back to the pre-synaptic neuron and 
surrounding cells, perhaps to say: "I got the message."

"The ability to visualize nitric oxide at the nanomolar level in 
cells and tissues should be of tremendous benefit in determining its 
effects on long term potentiation (LTP) and neuronal development," 
commented Michael J. Clarke, a chemist at the National Science 
Foundation, which funded this research.

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Elizabeth A. Thomson
Assistant Director, Science & Engineering News
Massachusetts Institute of Technology
News Office, Room 11-400
77 Massachusetts Ave.
Cambridge, MA  02139-4307
617-258-5402 (ph); 617-258-8762 (fax)
<thomson at mit.edu>

<http://web.mit.edu/newsoffice/www>
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