APRIL 2003

Bioluminescence reveals protein-protein interactions

By: Karen Sandrick

CONTEXT: The protein-protein interactions that regulate programmed cell death, differentiation, signal transduction, and migration can be observed in many ways-but until recently, they were always seen in isolated cellular configurations under a microscope. The Crump Institute for Molecular Imaging in Los Angeles has developed an optical bioluminescence method that shows how intracellular networks communicate in whole, living animals through the use of a novel split-reporter protein technology.

RESULTS: The researchers split the firefly luciferase reporter protein in two, attached half of the molecule to each of the two test proteins, and measured luciferase expression with a CCD camera when the molecules came together again after protein-protein interaction (Proc Natl Acad Sci USA 2002 Nov 26;1999[24]:15608-15613).

IMAGE: Optical imaging of a live mouse was performed several times over a 24-hour period. Four regions (A-D) were interrogated. Sites A, C, and D served as controls; site B contained two interacting proteins (myoD and ID). When these two proteins interact they bring together (complement) two split proteins called split firefly luciferase. This complementation was detected in a cooled optical CCD camera. The light signal measured in photons/sec/cm2/steridian(sr) reflects the underlying biochemical process of protein-protein interaction.

IMPLICATIONS: "Now that drugs are being developed to block a particular protein-protein interaction, we have a method that may be able to detect it," said Dr. Sam Gambhir, director of the Crump Institute.