Shedding light on luminescence: Scientists visualize structure of the photoprotein aequorin

May 17, 2000

Anyone who's spent time at a beach on a warm summer night has seen them: luminescing ctenophores that twinkle like tiny stars in moonlit waters. No one knows exactly why these comb jellies flicker and glow, but Marine Biological Laboratory (Cape Cod, Massachusetts) senior scientist Osamu Shimomura now knows a lot more about the structure of the remarkable protein that is not only responsible for this phenomenon, but has proved to be an invaluable tool for researchers studying the role of calcium in disease.

In this week's issue of the journal Nature, Shimomura and his colleagues James Head from Boston University, Katsunori Teranishi from Mei University (Japan), and Satoshi Inouye from Chisso Corporation (Japan), describe the three-dimensional crystal structure of aequorin, the photoprotein that illuminates jellyfish, ctenophores and many other luminescing organisms. The study was supported by the National Science Foundation.

"The work of these investigators has clearly demonstrated how insights into the structure of a protein lead to insights into its biological function...with great potential for molecular modeling and designing new sensors for monitoring other ions in a cell," according to Ralph Addison, program director in NSF's biophysics program, which supported this work.

Since his discovery of aequorin 38 years ago, Shimomura's life's work has been devoted to shedding light on luminescence-a complex chemical reaction within an organism's cells that results in the release of energy in the form of light instead of heat. Shimomura determined years ago that aequorin glows blue when tiny amounts of calcium bind to it.

This discovery led to the use of aequorin as an important biomedical tool for tracking the movement of calcium within cells. Calcium plays a crucial role in the regulation of a variety of biological processes including fertilization, muscle contraction, and the transmission of nerve impulses. Clinicians also recognize that calcium is significant in the pathology of a number of neurological diseases, including Alzheimer's.

Much has been learned over the years about aequorin and its regenerated form, apoaequorin. But, says Shimomura, "We've been working blind for many years." Until now, no one has been able to visualize the actual three-dimensional crystal structure of this important protein, something Osamu Shimomura has dreamed of doing since first discovering aequorin.

Now that Shimomura and his colleagues know the exact structure of aequorin, they'll be better able to study how the protein functions in concert with other chemicals, and, possibly, enhance its usefulness as a biological marker.

"One of the most exciting outcomes of knowing the structure of aequorin is that it offers the potential for us to perhaps 'custom' design molecules that are able to sense different molecules or ions," explains co-author James Head of Boston University. "These would then 'wink' at us, with light emission, when a certain molecule is encountered. It is possible that, based on the current structure, we may be able to engineer the protein to respond to different ions at different ranges of concentrations, and conceivably combine the aequorin structure with other protein domains that bind entirely different molecules to produce completely new sensors. This has the potential to provide a family of biosensors for use in biological systems, and, under the right conditions, possibly also for use in industrial settings."
Media contact: Pam Clapp, MBL

Program contact: Ralph Addison

National Science Foundation

Related Protein Articles from Brightsurf:

The protein dress of a neuron
New method marks proteins and reveals the receptors in which neurons are dressed

Memory protein
When UC Santa Barbara materials scientist Omar Saleh and graduate student Ian Morgan sought to understand the mechanical behaviors of disordered proteins in the lab, they expected that after being stretched, one particular model protein would snap back instantaneously, like a rubber band.

Diets high in protein, particularly plant protein, linked to lower risk of death
Diets high in protein, particularly plant protein, are associated with a lower risk of death from any cause, finds an analysis of the latest evidence published by The BMJ today.

A new understanding of protein movement
A team of UD engineers has uncovered the role of surface diffusion in protein transport, which could aid biopharmaceutical processing.

A new biotinylation enzyme for analyzing protein-protein interactions
Proteins play roles by interacting with various other proteins. Therefore, interaction analysis is an indispensable technique for studying the function of proteins.

Substituting the next-best protein
Children born with Duchenne muscular dystrophy have a mutation in the X-chromosome gene that would normally code for dystrophin, a protein that provides structural integrity to skeletal muscles.

A direct protein-to-protein binding couples cell survival to cell proliferation
The regulators of apoptosis watch over cell replication and the decision to enter the cell cycle.

A protein that controls inflammation
A study by the research team of Prof. Geert van Loo (VIB-UGent Center for Inflammation Research) has unraveled a critical molecular mechanism behind autoimmune and inflammatory diseases such as rheumatoid arthritis, Crohn's disease, and psoriasis.

Resurrecting ancient protein partners reveals origin of protein regulation
After reconstructing the ancient forms of two cellular proteins, scientists discovered the earliest known instance of a complex form of protein regulation.

Sensing protein wellbeing
The folding state of the proteins in live cells often reflect the cell's general health.

Read More: Protein News and Protein Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to