Biosynthesis and Biological Function of Pectin
What is Pectin?

The cell wall of plants is a polysaccharide and protein rich macromolecular structure that is essential for plant form and function. It is also the meeting point between the plant and its symbionts or pathogens. Pectin is a major component of plant primary walls and is involved in plant growth, defense, and development. Pectin is also a food fiber, and is economically important as a nutritional and gelling agent. The research goals in the Mohnen laboratory are to understand pectin biosynthesis and the biological functions of pectin.

The main research project in the Mohnen laboratory is based on the premise that the most direct way to elucidate the biological functions of pectin is to understand how pectin is biosynthesized. The bulk of our research examines how the pectic polysaccharide homogalacturonan (HGA) is synthesized. HGA is a linear polymer of a alpha-1, 4-linked galactosyluronic acid that makes up ~60% of the pectic polysaccharides.

We previously identified a 4-alpha-glacturonosyltransferase (GalAT) that transfers GalA from UDP-GalA onto HGA or oligogalacturonides using plant membrane preparations. We specifically described an Arabidopsis gene GAlactUronosyl Transferase 1 (GAUT1) that encodes an enzymatically proven GalAT. Subsequent analysis of the Arabidopsis genome led us to propose the 15-member GAUT gene family that contains GAUT1, and a 10-member GAUT-Like (GATL) family. Current efforts focus on proving the function of the 25 proposed pectin biosynthetic genes. Our strategy includes heterologoous expression of the genes, studies of GAUT protein complexes, and analysis of gene mutants in Arabidopsis.

Investigations into beneficial aspects of pectin on human health is a developing research area in the Mohnen laboratory. Pectin has multiple beneficial effects on human health including lowering of blood cholesterol and serum glucose levels and the potential inhibition of cancer growth and metastasis. Some of these benefits may occur via the induction of apoptosis (programmed cell death) and/or the interfering with ligand:receptor interactions. However, neither the specific pectin structure containing apoptotic inducing activities, nor the precise molecular mechanisms of pectin's activities are known.

In a collaborative project with Dr. Vijay Kumar (Medical College of Georgia), we are studying the effects of different pectins on cell apoptosis and cancer metastasis in human prostate cancer cell lines. Prostate cancer is the most common malignancy and the second leading cause of death in American men. The goal of our studies is to determine the molecular mechanisms by which pectin inhibits prostate cancer. A longer-term goal is to develop recommended diet changes and/or pectin-based strategies to combat the incidence and lethality of prostate and other cancers, and to promote human health.