Dimerization of Neural Cadherin in the Presence of Low Calcium

Author

Kyler PisciottaFollow

Date of Award

Spring 5-9-2020

Document Type

Undergraduate Thesis

Department

Chemistry and Biochemistry

First Advisor

Susan Pedigo

Relational Format

Dissertation/Thesis

Abstract

Cell-cell linkage is a necessity for proper tissue function and stability in many biological systems. One moiety that allows for the proper linking of cells to one another is a family of molecules known as cadherins. This family of proteins can be found within the membrane of many different types of cells and the extracellular portions of the cadherin proteins interact with those of other cells to link adjacent cells together via the formation of a dimer complex. The presence of calcium (Ca²⁺) is of crucial importance for the formation of this cadherin dimer. In this study, we focused on the dimerization of neural (N-) cadherin proteins in the presence of low calcium concentrations. Consideration of low calcium concentration is of particular importance due to the existence of N-cadherins at neurological synapses. N-cadherin is the marker for long term potentiation within synapses, an environment with exceptionally low Ca²⁺ concentration compared to that of normal extracellular space (40µm vs 1mM). We hypothesized that this low calcium content would decrease the fraction of cadherins that existed in the dimer conformation. In order to test this theory, we determined the equilibrium constants of N-cadherin at decreasing Ca²⁺ concentrations (1000µM, 100µM, and 40µM) at physiological pH. This experiment required using a chelator (EDTA) to trap the dimer for all three Ca²⁺ concentrations. Then, using size exclusion chromatography (SEC), the concentration of N-cadherin in the dimeric state was determined, from which the equilibrium constants were calculated. Circular Dichroism (CD) spectroscopy was also used to monitor the secondary structural changes of the N-cadherin protein at each Ca²⁺concentration. Results from this experiment are consistent with a change in the equilibrium to favor the monomeric state of N-cadherin at the lower Ca²⁺ concentrations found in neurological synapses. This observation implies that excitatory synapses have plasticity due to the weak dimerization affinity in the prevailing calcium concentration.

Recommended Citation

Pisciotta, Kyler, "Dimerization of Neural Cadherin in the Presence of Low Calcium" (2020). Honors Theses. 1369.
https://egrove.olemiss.edu/hon_thesis/1369

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