Thesis (Ph. D.)--Washington State University, May 2007. / Includes bibliographical references.

The sarcoplasmic reticulum (SR) of skeletal muscle is an intracellular membraneous network that, through the cyclical release and re-uptake of Ca²⁺ into and from, respectively, the cytoplasmic space, regulates myofilament shortening and, therefore, muscle contraction. SR derived from the terminal cisternae (HSR) demonstrates the property of Ca²⁺-induced Ca²⁺ release. Upon attainment of a threshold intralumenal Ca²⁺ load, application of a small pulse of extralumenal Ca²⁺ stimulates the release of a pool of intralumenal Ca²⁺ via the ligand gated Ca²⁺ permeable pore of the Ca²⁺ release channel/ryanodine receptor complex. It was hypothesised that intralumenal Ca²⁺ regulates the opening of the release channel. HSR vesicles were purified from skeletal and cardiac muscle by a novel technique. Structural characterisation of these membranes demonstrated an enrichment of harvested fractions in the Ca²⁺ release channel and the intralumenal Ca²⁺ binding protein, calsequestrin. In radiometric studies, skeletal HSR vesicles were shown to bind ryanodine with high capacity at both low and high affinity sites, with 2 fold stimulation of Ca²⁺ accumulation by the polyorganic cation Ca²⁺ channel blocker, ruthenium red. HSR vesicles passively loaded Ca²⁺. Passive loading of HSR vesicles with Ca²⁺ was found to be non-linearly dependent upon the concentration of Ca²⁺ within the loading medium. This suggested the presence of 2 intralumenal Ca²⁺ binding sites with different affinities for Ca²⁺. A spectroscopic dual-wavelength assay of Ca²⁺ release was developed that took advantage of peculiar spectral properties of the metallochromic sensitive dye Antipyrylazo III. In the presence of mM MgATP and mM Mg2+ the initial fast phase of HSR Ca²⁺ was well resolved. Evidence was presented that initial rapid uptake was associated with high affinity binding to an intralumenal compartment. Ca²⁺ -induced Caz+ release was shown to occur with a threshold loading of intralumenal Ca²⁺. The intralumenal Ca²⁺ threshold for Ca²⁺-induced Ca²⁺ release was decreased in the presence of ryanodine. Ryanodine induced Ca²⁺ release was also dependent upon the amount of intralumenal Ca²⁺. Ryanodine was also shown to inhibit sustained Ca²⁺-induced Ca²⁺ release by apparent inhibition of the binding of Ca²⁺ to intralumenal sites. These results suggested that junctional state transitions of the Ca²⁺ channel and calsequestrin were interdependent. Purified mM and mM Ca²⁺ activated neutral protease isoforms selectively cleaved the Ca²⁺ channel into 410 and 150kDa peptides with limited proteolysis. This was demonstrated in both HSR vesicles and the purified Ca²⁺ release channel. A novel 88kDa protein was also shown to be fragmented by both CANP isoforms. The identity of this prominent HSR associated protein remains obscure. CANP fragmentation of HSR protein elevated passive and active 4^Ca²⁺ loading in vesicles. This indicated that selective structural modification of the cytoplasmic portion of the release channel modified the comformational states of a intralumenal Ca²⁺ binding compartment in HSR vesicles. In spectroscopic studies, CANP proteolysis of HSR proteins increased the sensitivity to Ca²⁺ and ryanodine-induced Ca²⁺ release through decreases in the required intralumenal Ca²⁺ threshold for release. These functional alterations coincided with apparent single site cleavage of the release channel. Further proteolysis of the initial 410 and 150kDa peptides was without further significant effect upon function. Based upon the hypothesis that primary sequences rich in proline (P), glutamate (E), aspartate (D), serine (S) and threonine (T) (PEST regions) are recognition sites for CANP binding to substrates, a search for PEST regions within the Ca²⁺ channel was undertaken. It was tentatively proposed that two PEST regions near the N-terminal of the Caz release channel may represent sites close to the CANP cleavage site. The results of this work were discussed in relation to a possible role of Ca²⁺-induced Ca²⁺ release in regulating the patterning of Ca²⁺ cytosolic transients. The frequency and amplitude of cytosolic Ca²⁺ transients appear to be important in regulating protein expression. The requirement of intralumenal Ca²⁺-induced Ca²⁺ release may be a means by which the cyclical uptake and release of Ca²⁺ during muscle relaxation and contraction can be coordinated. This coordination may define the patterning of cytosolic Ca²⁺ transients. The increased sensitivity to Ca²⁺-induced Ca²⁺ release by HSR after CANP treatment may represent a means by which the patterning of cytosolic Ca²⁺ transients can be altered to effect changes in protein synthesis. / Graduate and Postdoctoral Studies / Graduate

No description available.

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily. The result of RAGE-ligand interactions augments the proinflammatory mechanisms acting in chronic inflammatory diseases. RAGE recognises a wide range of ligands that have no apparent structural similarities. It is unclear what controls this promiscuity of RAGE. The extracellular domain of RAGE has two potential glycosylation sites. It is speculated that N-linked glycosylation may have significant impact on ligand recognition, especially of S100 calcium binding protein ligands. Two objectives of this thesis were to establish whether S100A9 acts as a ligand for RAGE and to investigate whether glycosylation of RAGE has any influence on ligand recognition. These were achieved by generating two forms of RAGE. HEK 293 cells were transfected to express full-length, membrane-bound RAGE or a secreted form comprising the extracellular domain of RAGE. Site-directed mutagenesis of RAGE showed that asparagine at position 25 is the pre-dominant N-linked glycosylation site. The carbohydrate added to asparagine 25 was further modified to a non-sialylated carboxylated N-linked glycan, specifically recognised by monoclonal antibody GB 3.1. Binding studies showed that different RAGE ligands have individual requirements for glycosylation of the receptor. Binding of AGE-modified AGE-BSA or of S100B to RAGE occured independent of N-linked glycosylation of the receptor. RAGE also binds the S100 protein, MRP-14 (S100A9). In contrast to AGE-BSA or S100B, the non-sialylated carboxylated N-glycan expressed on RAGE is crucial for binding to MRP-14. However, RAGE produced in tunicamycin containing medium and thus lacking N-linked glycosylation, shows strong binding to MRP-14. It was concluded that two forms of binding are involved: the first mechanism relies on the non-sialylated carboxylated N-glycan attached to RAGE and acts in a "tethering" fashion. The second mechanism involves a conformational change of RAGE, which results in exposure of a binding site(s) and a more conventional receptor-ligand interaction. Another objective for this thesis is to study the expression of RAGE and its alternatively spliced variants. PCR analysis has revealed several variants of RAGE that result from alternative splicing mechanisms. The variant proteins are soluble due to a lack of membrane localising sequence. PCR results confirmed the presence of transcripts encoding for spliced variants of RAGE in several tumour cell lines. Among these were transcripts that should encode a soluble form of sRAGE 2. Furthermore, it was shown that sRAGE 2 transcript can be present in forms that contain the ligand-binding V-domain of RAGE or that are N-truncated and lack the V-domain. This is the first report of a soluble, N-truncated sRAGE 2 variant. The results in this thesis add to our knowledge of RAGE biology. MRP-14 (S100A9) is identified as a new ligand. The control of MRP-14/RAGE interaction relies on N-linked glycosylation of the receptor and further modification of the carbohydrate. "Tethering" or stronger receptor-ligand interactions are suggested as mechanisms for controlling RAGE recognition of multiple ligands. Soluble RAGE variants that lack or contain V-domain binding regions, and hence sites for glycosylation were produced. These have the capacity to compete with membrane-bound receptor for available ligand. The control of the expression of soluble RAGE variants, in concert with the control of various modification to carbohydrate expressed on the receptor, adds a level of complexity to ligand specificity. This may ultimately result in different paradigms of the inflammatory process.

Understanding the temporal and spatial changes in calcium concentration has been a difficult endeavor for many years due to the relatively small changes in calcium concentration during messenging events, the rapid changes upon physiological messenging, and the unavailability of fast, efficient, and sensitive sensors to detect calcium changes. In addition, the key factors in calcium binding have yet to be determined due to the metal-metal interactions, cooperativity, and conformational change involved in calcium binding to natural calcium-binding proteins. To overcome these obstacles and to engineer calcium sensors for in vivo studies of calcium signaling events, calcium binding sites have been engineered into Green Fluorescent Protein. The engineered binding sites demonstrate terbium binding affinity from 2-30 ƒÝM and calcium binding affinity from 50-100 ƒÝM. Site 177 demonstrates green fluorescence when expressed in mammalian cells and produces a response to calcium concentration changes when expressed in the cytosol. Addition of the cycle 3 mutations (M153T, V163A, F99S) to Site 177 allowed for increased brightness in the emission of the chromophore but still exhibited calcium response. The second generation Site 1 demonstrates fluorescence response to calcium concentration changes when expressed both in the cytosol and in the endoplasmic reticulum. Addition of M153T and V163A to Site 1 allowed for expression of fluorescent protein at 37 ¢XC in HeLa cells and at 30 ¢XC in bacteria. Site 1-M153T/V163A exhibits chromophore fluorescence response to calcium with a Kd of 100 ƒÝM and competition with Rhodamine-5N produced a calcium Kd of 107 ƒÝM. This designed sensor, Site 1-M153T/V163A is the first demonstration of a designed calcium binding GFP with calcium response measured both in vivo and in vitro.

Thesis (M. Sc)--York University, 2000. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 87-100). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ59208.

In this study the mechanisms of Ca²⁺-induced-Ca²⁺-release, effects of membrane depolarizations and the actions of pharmacological intracellular Ca²⁺-modulators were examined in cultured rat dorsal root ganglion (DRG) neurones. The whole cell configuration of the patch clamp technique was used to record action potentials, action potential after-potentials and voltage-activated calcium currents, (I_Ca), calcium-activated chloride currents, (I_CI(Ca)), and non-selective cation currents, (I_CAN), under current and voltage clamp recording conditions, respectively. A sub population of DRG neurones expressed action potential after-depolarizations and I_CI(Ca)tail currents which were due to activation of Ca²⁺-activated Cl^- channels as a result of Ca²⁺ entry. I_CANwas dominantly activated due to Ca²⁺ release from intracellular stores evoked by pharmacological Ca²⁺-releasing agents such as caffeine, ryanodine and dihydrosphingosine. Calcium-activated conductances were identified by estimating reversal potentials of the activated currents, using selective pharmacological blockers and extracellular ionic replacement studies. Calcium-dependence of activated currents was also examined by using high concentration of intracellular Ca²⁺ buffer, EGTA, to prevent elevation of intracellular Ca²⁺-levels and by rapidly buffering raised intracellular Ca²⁺ using intracellular 'caged Ca²⁺ chelator', diazo-2. The involvement of intracellular Ca²⁺- stores was examined by performing experiments in Ca²⁺-free extracellular recording medium and pharmacologically inhibiting release of Ca²⁺ from intracellular stores, using dantrolene. Ryanodine had complex actions on DRG neurones, which reflected its ability to mobilize Ca²⁺, deplete Ca²⁺ stores, and inhibit Ca²⁺ release channels. Ryanodine inhibited action potential after-depolarizations and I_CI(Ca)tail currents by interacting with intracellular stores and preventing amplification of Ca²⁺ signalling by CICR. It was found that CICR observed under physiological conditions in rat DRG neurones involves intracellular Ca²⁺stores which were sensitive to ryanodine. In addition to ryanodine sensitivity these intracellular Ca²⁺ stores could be mobilized by caffeine and dihydrosphingosine.

Thesis (Ph.D.)--Georgia State University, 2006. / Title from file title page. Jenny J. Yang, committee chair; Alfons Baumstark, Giovanni Gadda, committee members. Electronic text (405 p. : ill. (some col.)) : digital, PDF file. Description based on contents viewed Aug. 20, 2008. Includes bibliographical references (p. 380-405).

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Ulhas P. Naik, Dept. of Biological Sciences. Includes bibliographical references.

No description available.