Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Microbiology

Advisor

Robert E. Gundersen

Second Committee Member

Julie Gosse

Third Committee Member

Rebecca Van Beneden

Abstract

Chemotaxis is a complex process that relies on various integrated signal cascades. Many of these signal pathways incorporate by the heterotrimeric guanosine nucleotide-binding proteins (G proteins). Lipid modification including the post-translational modification, palmitoylation can be considered as a key factor for proper G protein function. Various models have been used to gain a deeper understanding of the role of G proteins in cell chemotaxis. The soil amoeba, Dictyostelium discoideum, is well-known for its use in chemotaxis studies. During the development phase of its life cycle, Dictyostelium cells rely on their ability to performed chemotaxis toward the chemoattractant cyclic adenosine monophosphate (cAMP). Although significant details have already been worked out for this signaling and response pathway, little is known about how the G protein signal platform (lipid raft) may be involved. To elucidate how this microdomain may be involved in the G-protein-mediated chemotaxis signal, a low-density membrane fraction was isolated using a detergent-free method. In basal state, Ga2 was enriched in the low-density membrane and this was dependent on Ga2 acylation. Blocking Ga2 activation had no effect on this association, while activation shifted Ga2 from the low-density fraction to higher density fractions. Shifting of the activated-Ga2 to the 20% gradient fraction was under the control of F-actin. Our findings suggest that lipid microdomains are the proper environment for the palmitoylated Ga2 and activation leads them to leave these low-density domains and to accumulate in the heavier fractions.

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