Date Approved

8-2015

Document Type

Thesis

Degree Name

Master of Science in Biomedical Sciences

Department

Cell Biology

College

Graduate School of Biomedical Sciences

First Advisor

Venkateswar Venkataraman, PhD

Committee Member 1

Robert Nagele, PhD

Committee Member 2

Yang Yang, PhD

Subject(s)

Neuronal Calcium-Sensor Proteins; Signal Transduction; Hippocalcin; Conserved Sequence; Tryptophan; Calcium

Disciplines

Cell Biology | Cellular and Molecular Physiology | Comparative and Evolutionary Physiology | Life Sciences | Medicine and Health Sciences | Molecular and Cellular Neuroscience | Molecular Genetics

Abstract

Changes in intracellular calcium levels play a very important role in cell signaling, in turn, affecting neuronal functions such as memory, learning and cell death. A class of proteins called Neuronal Calcium Sensor (NCS) proteins serves to modulate the functioning of the neuronal cells in response to changes in calcium levels, and prevent neuronal apoptosis. Structurally, all NCS proteins have 4 calcium-binding EF hand motifs, although EF1 does not bind to calcium in many members. All NCS proteins have an acyl modification at the N- terminus – where a myristoyl group is added post-translationally. Hippocalcin (HPCA) is an NCS protein, and shares 95% similarity in primary amino acid sequence with another major NCS protein, Neurocalcin delta (NCALD). HPCA and NCALD have 2 evolutionary conserved tryptophan residues at the 30th, and 103rd amino acid position. Based on structural analyses and preliminary data, we propose that these tryptophan residues are important for the calcium- dependent changes in HPCA. Mutation of the residues even to “conserved substitution” (namely phenylalanine) appears to have drastic effects in NCALD. We propose that mutation of the W to F residues (individually or together) would have decreased response to calcium when compared with the native HPCA protein, and the effects will be similar in W to F NCALD mutants. Three different parameters will be used to compare the proteins’ response to calcium: (i) tryptophan fluorescence to monitor local changes in structure around the tryptophan residues, (ii) native gel electrophoresis to monitor global changes; and (iii) gel filtration chromatography to monitor the oligomerization state.

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