Discovering cell surface proteins' behavior

PLOS ONE has just published the paper, N-glycoproteome of E14.Tg2a Mouse Embryonic Stem Cells.

Glycoproteins are membrane proteins and are often involved in human diseases. They facilitate communication between cells, and interactions with pathogens, such as viruses and bacteria, and communication with external environments.

SFU chemist Bingyun Sun and her colleagues have discovered how nature can vary the amount of a dominant sugar type (N-Glycan) on membrane proteins on a cell surface. The variation helps stabilize these proteins and facilitate their functioning.

The researchers verified their observation of a correlation between the number of sugars on a glycoprotein and its function in five animal species -- worms, flies, fish, mice and humans. This led to their realization that the correlation has been conserved through evolution.

To obtain the number of N-Glycans on proteins, the researchers used proteomics -- a combination of mass spectrometry (MS) and high-performance liquid chromatography (HPLC). In less than an hour, high-throughput technique identifies the exact place where N-Glycans attach on hundreds of glycoproteins.

The scientists analyzed cell surface glycoproteins in one type of mouse embryonic stem cells by genetically shutting down the Hypoxanthine Phosphoribosyltransferase (HPRT) gene in the cells.

As an aside, HPRT deficiency causes Lesch-Nyhan syndrome in humans, a metabolic disorder characterized by mental retardation and self-mutilation.

Sun says this deeper understanding of the correlation between sugars' positioning on glycoproteins and the proteins' functions will benefit medical researchers and the pharmaceutical industry.

"As membrane proteins, glycoproteins are biologically important," explains Sun, who is fluent in Mandarin and English, and is originally from Mailand China.

"They mediate cells' communication to their environment, thus governing a plethora of cellular processes and functions, including growth, development, immunity and aging.

"Understanding how membrane proteins adapt to better protect themselves will help us design better, less toxic drugs to treat diseases."

Backgrounder: Understanding surface cell proteins

Mass spectrometry(MS) is an analytical technique that measures the mass-to-charge ratio of charged particles.^[1] It is used for determining masses of particles, for establishing the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and other chemical compounds.

High-performance liquid chromatography(sometimes referred to as high-pressure liquid chromatography), HPLC, is a chromatographic technique used to separate a mixture of compounds in analytical chemistry and biochemistry with the purpose of identifying, quantifying or purifying the individual components of the mixture. HPLC is considered to be the most frequently used instrumental technique in analytical chemistry.

HPLC has many uses including medical (e.g. detecting vitamin D levels in blood serum), legal (e.g. detecting performance enhancement drugs in urine), research (e.g. separating the components of a complex biological sample, or of similar synthetic chemicals from each other), and manufacturing (e.g. during the production process of pharmaceutical and biological products).