The type Iα cGMP-dependent protein kinase (PKG Iα) is an essential regulator of vascular tone and systemic blood pressure. Located in the smooth muscle of resistance vessels, PKG Iα stimulates vasodilation through the phosphorylation of multiple intracellular substrates. Its primary regulator is the small molecule, 3',5'-cyclic guanosine monophosphate (cGMP); however, the Iα isoform can also be activated by oxidation. Despite the established physiological importance of PKG Iα, the structural underpinnings of these two activation mechanisms are largely unknown.
The work presented in this dissertation demonstrates the importance of the cGMP-binding domain A (CBD-A) in regulating both of these mechanisms of PKG Iα activation. Using a monomeric, N-terminally truncated form of PKG Iα (Δ53), Chapter 2 investigates the mechanism of inhibition through the autoinhibitory domain and the influence of dimerization on cooperative cGMP-dependent activation and cyclic nucleotide selectivity. We observed that autoinhibition occurs in cis, whereas cooperativity requires interprotomer contacts facilitated by the N-terminal dimerization domain. Furthermore, the loss of selectivity for cGMP over cAMP of this construct suggests the dimerization domain plays a critical role in preventing cross-reactivity with cAMP-dependent signaling. These observations culminate into an overarching model wherein binding of cGMP to CBD-A is necessary and sufficient for activation and cooperativity is driven by the dimerization domain.
Chapter 3 investigates the cysteine residues that mediate oxidation-dependent activation of PKG Iα. Using PKG Iα constructs with point mutations at specific cysteine residues, it was found that oxidation-dependent activation is driven by C117 in CBD-A. Furthermore, the interprotomer disulfide bond that forms in the dimerization domain at C42 does not contribute to this mechanism. Finally, we propose a model wherein the disulfide bond that forms between C117 and the adjacent cysteine at position 195 acts as a protective mechanism to prevent activation and higher oxidation states form contacts with nearby residues in the linker region of PKG Iα to disrupt binding of the adjacent autoinhibitory domain to the catalytic domain.
Finally, Chapter 4 provides a discussion of the results presented herein in context with previous studies and suggests future directions for the PKG field.
| Identifer | oai:union.ndltd.org:uvm.edu/oai:scholarworks.uvm.edu:graddis-1950 |
| Date | 01 January 2018 |
| Creators | Sheehe, Jessica Lynne |
| Publisher | ScholarWorks @ UVM |
| Source Sets | University of Vermont |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate College Dissertations and Theses |
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