Sugar Plays Key Role In How Cells Work

[Guest guest]

Sugar Plays Key Role In How Cells Work

http://medicalnewscenter.com/out/out.cgi?

http://www.sciencedaily.com/releases/2008/10/081020171442.htm

s Hopkins scientists were dubious in the early 1980s when they

stumbled on small sugar molecules lurking in the centers of cells;

not only were they not supposed to be there, but they certainly

weren't supposed to be repeatedly attaching to and detaching from

proteins, effectively switching them on and off.

The conventional wisdom was that the job of turning proteins on and

off -- and thus determining their actions -- fell to phosphates, in a

common and easy-to-detect chemical step in which phosphates fasten to

and unfasten from proteins; a process called phosphorylation.

Now, after decades of investigating the " new " sugar-based protein

modification they discovered, the s Hopkins team admits that they

themselves were surprised by their latest results. Published recently

in the Proceedings of the National Academy of Sciences, their

findings show that the surreptitious sugar switch is likely as

influential and ubiquitous as its phosphate counterpart and, indeed,

even plays a role in regulating phosphorylation itself.

More to the point, the work has implications for finding new

treatments for a number of diseases such as diabetes,

neurodegeneration and cancer, because the new switches form yet

another potential target for manipulation by drugs.

" Like dark matter in the cosmos, it's hard to find even though it's

very abundant, " says Gerald Hart, Ph.D., the DeLamar Professor and

director of biological chemistry at the s Hopkins School of

Medicine, referring to the sugar (O-GlcNAc, pronounced oh-GLICK-nac)

that carries out GlcNAcylation.

For years, Hart's team thought of GlcNAcylation as phosphorylation's

foil; a simple, classic case of either-or. New technologies involving

molecular sleuthing with a mass spectrometer allowed them to measure

the extent to which the addition of sugar to proteins affects

phosphorylation.

Of 428 sites on which phosphate was being added to and taken off of

proteins, all responded in some way to increased O-GlcNAc: 280

decreased phosphorylation and 148 increased phosphorylation.

" The influence of sugar is striking, " Hart says. " The presence of O-

GlcNAc causes the enzymes that add the phosphate to do something

different, and this cross-talk itself can modify proteins. "

Because both sugar and phosphate modifications are linked to how

cells work, they are fundamental to understanding and eventual

control of the molecular processes that underlie many diseases.

" With regard to cancer, diabetes and Alzheimer's, " says Hart, " most

people in the world today have been studying the yang

(phosphorylation) but not the yin (GlcNAcylation). There's another

whole side that people were unaware of where diabetes diagnostics and

cancer therapies could be targeted. "

The research was funded by the National Institutes of Health.

Authors on the paper are Zihao Wang, Marjan Gucek and Gerald W. Hart,

all of s Hopkins.