Understanding the Chemical Basis of Neuronal Development and Communication: I. The Role of Fucose α(1-2) Galactose Carbohydrates in Neuronal Growth. II. Structure-Function Analysis of Chondroitin Sulfate in the Brain

Citation

Gama, Cristal Ivette (2009) Understanding the Chemical Basis of Neuronal Development and Communication: I. The Role of Fucose α(1-2) Galactose Carbohydrates in Neuronal Growth. II. Structure-Function Analysis of Chondroitin Sulfate in the Brain. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/CDGH-MJ49. https://resolver.caltech.edu/CaltechETD:etd-10302008-123855

Abstract

Although carbohydrates are known to participate in many processes including inflammation and cancer metastasis, their functional roles are only beginning to be understood on a molecular level. Unlike DNA and proteins, carbohydrate structures are not template-encoded and are challenging to detect in vivo and manipulate for structure-function analyses. New tools are needed to complement biochemical and genetic approaches to advance our understanding of carbohydrates and their physiological roles. We seek to understand the roles of carbohydrates in regulating the structure and function of proteins in the brain. Our focus is on two modifications that are important in neuronal communication and development: fucosylation (Part I) and chondroitin sulfate modifications (Part II).

In Part I, we describe our progress in elucidating the molecular mechanisms by which fucosyl saccharides regulate neuronal communication. Previous studies have shown that preventing formation of fucoseα(1-2)galactose saccharides causes reversible amnesia in animals, suggesting that these sugars play essential roles in learning and memory. However, proteins expressing the fucoseα(1-2)galactose epitope or proteins binding this epitope have not been identified. Using chemical probes, we established that fucoseα(1-2)galactose associated proteins participate in a novel carbohydrate-mediated pathway for regulating neuronal growth. Additionally, we found that fucoseα(1-2)galactose glycoproteins are prevalent in developing brain and that synapsin Ia/Ib are the major fucoseα(1-2)galactose glycoproteins in adult brain. In our attempts to identify Fucα(1-2)Gal lectins, we have established that multivalent polymers enhance our ability to capture and characterize such proteins.

In Part II, we describe our efforts toward understanding the role of chondroitin sulfate glycosaminoglycans in neuronal development. Chondroitin sulfate glycosaminoglycans are structurally complex and heterogeneous in nature, thus hampering efforts to understand their precise biological roles. It is thought that chondroitin sulfate activity is dictated by a sulfation code, where distinct sulfation sequences are spatially and temporally regulated. We have developed a chemical approach to evaluate the structure-activity relationship of chondroitin sulfate as it effects neuronal growth. We generated the first synthetic library of well-defined chondroitin sulfate oligosaccharides containing various sulfation sequences and have demonstrated that the chondroitin sulfate-E sequence is a stimulatory motif that promotes the growth of several neuron types. Moreover, we determined that chondroitin sulfate-E stimulation was facilitated through activation of the midkine/PTPζ and BDNF/TrkB pathways.

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