The results underscore the importance of glycosylation attachment of a sugar to a protein -- as a way cells control proteins' activities, the scientists report in the April 16 issue of the Proceedings of the National Academy of Sciences. The scientists found that at least two proteins involved in passing along insulin's message were unlikely to work properly when coated in extra sugar.

Type 2 diabetes, the most common form in adults, occurs when muscle, fat and other tissues stop responding to insulin's signals to mop up sugar from the blood. The resulting high blood sugar, if uncontrolled, can lead to blindness, amputation and death. Understanding sugar's precise influence on insulin's activity may help improve treatment and prevention, scientists hope.

"Cells don't respond to insulin itself. Instead, a whole cascade of events, set in motion by insulin, eventually causes cells to take in sugar," explains Gerald Hart, Ph.D., professor and director of biological chemistry in the school's Institute for Basic Biomedical Sciences. "We now have an explanation of how sugar can affect these signals, and even a hypothesis for how high blood sugar could cause tissue damage in diabetes -- by improperly modifying proteins."

Hart's lab discovered 18 years ago that sugar is used routinely inside cells to modify proteins, turning them on and off. The more commonly known protein-controller, phosphate, actually binds to some of the same building blocks of proteins as sugar does. If proteins have too many sugars on them, they can't be controlled properly by the cell and are unlikely to work correctly, suggests Hart.

"We think we've come across a major mechanistic reason for insulin resistance," says Hart. "These cells developed insulin resistance
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Contact: Joanna Downer
jdowner1@jhmi.edu
410-614-5105
Johns Hopkins Medical Institutions
15-Apr-2002