Laser untangles membrane measurements

VANDERBILT (US) — A new laser technique that can measure interactions between proteins tangled in a cell’s membrane is expected to help in the discovery of new drugs.

About 30 percent of the 7,000 proteins in a human cell reside in its membrane, initiating 60 to 70 percent of the signals that control the operation of its molecular machinery. As a result, about half of the drugs currently on the market target membrane proteins.

Individual membrane proteins are extremely hard to purify, making structural information difficult to obtain.

Existing methods remove the membranes from their natural environment or modify the membranes in a variety of different ways, such as attaching fluorescent labels, in order to analyze membrane protein activity.

“In addition to being expensive and time-consuming, these modifications can affect the target membrane’s function in unpredictable ways,” says Darryl Bornhop, professor of chemistry at Vanderbilt University.

The laser-based technique, called backscattering interferometry (BSI), precisely measures the binding force between membrane proteins and both large and small molecules in a natural environment.

The research is reported online in the journal Nature Biotechnology.

“This is a powerful tool and a major advance in measuring membrane protein interactions,” says Lawrence Marnett, professor of cancer research, who was not involved in the study.

Lasers aid measurement

BSI measures the binding force between two molecules mixed in a microscopic liquid-filled chamber by shining a red laser like those used in barcode scanners through it.

When the geometry of the chamber is correct, the laser produces an interference pattern sensitive to what the molecules are doing. If the molecules begin sticking together, for example, the pattern begins to shift.

In the new study, the researchers created synthetic membranes that contained a small protein, called GM1, that is a primary target that cholera toxins bind with in order to get into a cell.

When they mixed these membranes with cholera toxin B, they measured a binding force consistent with that obtained by other methods.

Similar validation tests were performed with naturally derived membranes and three different membrane proteins—associated with breast cancer, pain and inflammation, and the neurotransmitter GABA known to aid in relaxation and sleep and to regulate anxiety.

When they mixed the membranes containing each of these proteins with molecules known to bind with them, the BSI technique provided measurements that agreed with the values obtained by other methods.

The research was supported in part by the National Institutes of Health.

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