The Dimerization Kinetics of NCAD12 with a Mutated Cis-X-Pro Bond

McClearn, Victoria (2015) The Dimerization Kinetics of NCAD12 with a Mutated Cis-X-Pro Bond. Undergraduate thesis, under the direction of Susan Pedigo from Chemistry and Biochemistry, University of Mississippi.

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Abstract

VICTORIA RAE McCLEARN: DIMERIZATION KINECTICS OF NCAD12 P16A (Under the direction Dr. Susan Pedigo) Calcium binding causes a conformational change into a strand swapped dimer for the cadherins. However, regardless of the sequence similarity for Epithelial Cadherin (ECAD) and Neural Cadherin (NCAD), they respond to the presence of calcium differently. For NCAD, the rate of assembly and disassembly depends upon the presence of calcium, whereas for ECAD the rate of exchange is independent of calcium. Studies into a kinetic model to explain the differences between the rates have been recently conducted. It is believed that ECAD uses an “X-dimer” intermediate between the monomer and dimer state. However, there is no kinetic model for the transition of monomer to dimer for NCAD. The purpose of the experiment was to mutate the 16th amino acid residue in NCAD from a proline to an alanine in order to investigate the potential kinetic role of this residue. The presence of the double cis-X-pro bond between the 14th and 19th residues differs from that of ECAD. There are two cis-X-pro bonds in NCAD and only one in ECAD, which may affect the rate of dimer formation. Stability, calcium binding affinity and dimer assembly studies resulted in interesting observations about the differences between NCAD12 P16A and wild type NCAD12. First, the P16A mutation does not affect the global stability of the protein, or the average calcium binding affinity. However, the calcium binding transition is distinctly more cooperative than seen in titrations of NCAD12 wild type. Secondly, the P16A appears to increase the Kd of dimerization. Thirdly, the rate of assembly of NCAD12 P16A dimers is dependent upon incubation time in calcium. In conclusion we notice an interesting and dramatic effect on both the kinetics and equilibria of dimerization in the P16A mutant of NCAD12. It further supports the supposition from the X-dimer literature that the N-terminal end of the βB-strand is important for the kinetics of dimerization, but shifts focus from the basic residue in position 14 to βB-strand conformation generally.

Item Type: Thesis (Undergraduate)
Creators: McClearn, Victoria
Student's Degree Program(s): B.A. Biochemistry
Thesis Advisor: Susan Pedigo
Thesis Advisor's Department: Chemistry and Biochemistry
Institution: University of Mississippi
Subjects: Q Science > QD Chemistry
Depositing User: Victoria McClearn
Date Deposited: 06 May 2015 19:57
Last Modified: 23 Oct 2015 19:14
URI: http://thesis.honors.olemiss.edu/id/eprint/352

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