Shedding Light -- On How Jellyfish Glow -- Calcium Is Creature's Inner Lamp
Seattle Times Science Reporter
Biochemistry: What makes some jellyfish glow? Answering the question has shed light on how the ebb and flow of calcium - needed to turn on bioluminescent jellies' light - also directs crucial functions in the human body.
FRIDAY HARBOR - From waterfront Lab 1 at the end of a row of dense trees, John Blinks is at work trying to make a better photoprotein.
It wasn't always this way. Time was when Blinks, a retired physiology professor at the University of Washington Medical School, would make regular pilgrimages to Friday Harbor, arguably the best place in the world to collect jellyfish, free-floating, diaphanous creatures that contain a protein that might answer some of the human cell's most vexing questions. In the boom years, Blinks could stand in one spot and fill a dozen buckets with up to 10,000 jellies in a couple of hours.
Now Blinks lives in Friday Harbor full time, and many jellies have vanished. No matter. There's little need to harvest live jellies anymore. What nature has coaxed to move to other waters, Blinks and Russian colleagues can clone in the lab. And they can do nature one better, twisting the tail on a DNA molecule as a child might roll a curl, creating a hybrid photoprotein that's faster and less fussy than the natural version.
Calcium: the body's conductor
Why can photoproteins, the flash-bulb proteins that jellies such as Aequorea victoria turn on to give the outer edge of the creature's bell-shaped body a bluish or greenish glow? The answer centers on calcium.
The jelly's light switch turns on in the presence of calcium ions, and the calcium ion is one of nature's favorite intercellular messengers, Blinks said.
Calcium is the conductor in the human body's orchestra, regulating body functions by changing intercellular calcium-ion concentration. Whenever you tense a muscle or waggle a finger; whenever your heart pounds out a beat, pulsing blood through a tangle of veins and arteries, calcium has prompted the muscle to act, contract or twitch.
To know how those calcium concentrations change, you need a way to measure it. Injecting a photoprotein - a protein that glows when calcium concentrations are up and dims when they go down - into a cell is one such measuring tool.
About 30 years ago, Osamu Shimomura was the one making the pilgrimage to the University of Washington's Friday Harbor Lab to learn more about how jellies glow. Shimomura, his wife and an assistant piled into a new station wagon that Frank Johnson drove for 12 hours a day, seven days straight, to get to the West Coast from Princeton University.
As Shimomura recounts in "Discovery of Aequorin," a paper published by The Biological Bulletin, Johnson knew that a freeze-dried "squeezate" extracted from the bioluminescent jelly Aequorea would emit light when mixed with water. It wasn't clear why. Did jellies glow as fireflies and bacteria did, in a process that requires oxygen?
Days of trial and error and more error forced Shimomura to think beyond what was already known about other bioluminescent creatures, imagining the unknown chemical reaction while drifting in a rowboat, meditating under sunny skies, floating as jellies do with the current.
Shimomura's breakthrough was theorizing that a different protein was involved in the light-emitting reaction and that the actions of that protein might be stilled by a pH change. Increase the acidity enough and the enzyme or protein might be slowed, then restarted.
The magic pH level was 4.0. A bit of baking soda (sodium bicarbonate) turned the light back on. But the light became "explosively strong" when Shimomura added seawater. He quickly deduced that calcium++, a calcium ion readily available in salt water, is the jelly's light switch.
Shimomura also learned he could extinguish the glow with EDTA, a compound that gets rid of calcium, Blinks said. The glow rekindled when more calcium was added.
The team collected jellies for hours, taking breaks just for lunch and dinner, snipping the rings that contained the light organs. Ten thousand specimens yielded an extract that returned to Princeton packed in dry ice. After purification and further testing, the team in 1962 had a protein that emitted light when just a trace of calcium was added - with or without oxygen. They named the protein "aequorin" after the jellies in which it's naturally found.
"Aequorin is an extraordinary protein containing a large amount of energy that can be released when calcium is added; thus it resembles a charged battery that releases the energy when short-circuited," Shimomura wrote.
The next step was somehow getting the protein inside a muscle. Maybe the cell would flash.
Blinks was the first to try. C.C. Ashely and E.B. Ridgway were the first to succeed in 1967 at the Friday Harbor Lab, using single muscle fibers from a barnacle. Hundreds of other papers followed.
The concept is so standard now that a businessman has come up with a playful attempt to harness the glow power to make transgenic brewer's yeast to create a light-emitting beer.
Blinks is less cheery. He has refused to become a member of the project's advisory committee. "You can never predict what kind of toxic effects these things might have. I agree with him (that) it's probably safe, but probably's not good enough."
Utilizing the glow
Through the years, the glow power of various creatures has been tapped for various ideas, ingenious to nefarious.
During World War II, for instance, the Japanese military considered using a dried extract from the light-emitting sea firefly to read maps at night and for marking the backs of soldiers, making it easier for them to follow each other through dark, thick jungles, Shimomura said.
The plan failed when ships containing the dried ostracod Cypridina were sunk by torpedoes and samples ruined by humidity. What remained in Japan was donated by the U.S. Navy to the Princeton lab where Shimomura worked. "The material still maintains good luminescence ability when rubbed on hands with water, after 55 years of being collected," he wrote in an e-mail message.
Thirty-some years after Shimomura, Blinks now occupies Lab 1. The next step for him is the search for a better photoprotein than aequorin.
Obelin, for example, is an Olympic sprinter, by comparison. If you want to measure the change in calcium concentration in, for example, a fast-moving nerve, you need a speedy indicator that can respond within a few milliseconds. Aequorin's not that fast off the blocks, Blinks said.
Magnesium can put a full-court press on aequorin, competing with calcium for binding sites that normally regulate illumination in the protein portion of the photoprotein. Oblein doesn't have such sensitivity and isn't slowed by magnesium as aequorin is.
Obelin comes from the hydroid Obelia longissima, a sea animal that looks like a plant. Russian colleagues collected samples from the White Sea and extracted obelin. From that a molecular biologist cloned the gene in Friday Harbor.
Back in Russia, scientists modified the three calcium binding sites, changing them to reduce their affinity. Because the sites no longer have a free carboxyl in the right place, it's like turning off each of the three lights that illuminate a room.
Blinks and colleagues are trying to understand the role of the three calcium ions that turn on the luminescence. Would one binding site be enough? How are the messages transmitted to light-emitter coelenterazine that now is the time to glow?
What practical application might there be from such research?
"From my perspective, the most important practical application - and this may not be everyone's idea of practical - is to build better tools for research. The practical application . . . will be a step beyond," Blinks said. "You never know when the information you gain seeking to understand turns out to be just what someone needed to build something better."
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