Dimorphic Leishmania donovani parasites exist as promastigotes in the sandfly vector and differentiate into amastigotes once injected into the skin of human hosts during a blood meal. The mechanisms and signals that are involved in triggering differentiation are not well understood in Leishmania. We have investigated whether tyrosine phosphorylation is a possible signalling component. Differential levels of tyrosine-phosphorylated proteins were observed in extracts from in vitro promastigote and amastigote cultures, with an overall reduction in the latter stage. Following this observation, the inhibition of tyrosine phosphorylation was examined in promastigotes using Tyrphostin AG1433, a broad-spectrum tyrosine phosphorylation inhibitor. AG1433 treated in vitro promastigote cultures differentiate into amastigote-like morphology, have reduced tyrosine phosphorylation level, and express the amastigote-specific marker A2 proteins. Our studies demonstrate that signal transduction mechanisms involving tyrosine phosphorylation/dephosphorylation events are involved in controlling L. donovani promastigote differentiation into amastigote forms.

Kinases play a crucial role in regulating cellular signaling cascades, making them therapeutic targets for several human diseases. In human cancers, mis-regulation and mutations of kinases such as EGFR (epidermal growth factor receptor) have been found to drive malignant transformation. Due to the conserved structural elements of protein kinases, the majority of kinase inhibitors available have a tendency to inhibit multiple targets. The biological impact of this promiscuity is insufficiently defined and the prevalence of cellular compensatory mechanisms additionally varies the clinical responses to drug treatment. In order to understand the relationship between selectivity and efficacy, prior to clinical trials, it is essential to characterize how inhibitors interact with the kinome within a cellular context. Monitoring inhibitor-target interactions generally involves in vitro assaying with purified proteins or protein domains, which compromises the native integrity of the kinases. Cellbased assays either gain outcomes from bulk populations that average out cell variance or phenotypic assays that lack molecular resolution. To obtain information on drug interactions on a single cell level, we have developed a method to measure the direct binding of kinase inhibitors to their targets in situ and in vivo. Kinase inhibitors are chemically tagged with fluorophores that serve as acceptors to genetically tagged donor fluorophores on the enzyme and the interaction is measured using FRET-FLIM. With epidermal growth factor receptor (EGFR) and irreversible EGFR inhibitors as the model system, this approach has been applied to image inhibitor-kinase interactions in live and fixed cells. Using this method, a small panel of tyrosine kinase targets, and labeled inhibitors, we were able to investigate the cross-specificity within the panel. Additionally it was found that the specificity of inhibitors for specific kinase conformations enables the distinction between EGFR in the active and inactive conformation by the inhibitor-probes. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Biomimetic peptides are autonomously folding secondary structural units designed to serve as models for examining processes that occur in proteins. Although de novo biomimetic peptides are not simply abbreviated versions of proteins already found in nature, designing biomimetic peptides does require an understanding of how native proteins are formed and stabilized. The discovery of autonomously folding fragments of ribonuclease A and tendamistat pioneered the use of biomimetic peptides for determining how the polypeptide sequence stabilizes formation of alpha helices and beta hairpins in aqueous and organic solutions. A set of rules for constructing stable alpha helices have now been established. There is no exact set of rules for designing beta hairpins; however, some factors that must be considered are the identity of the residues in the turn and non-covalent interactions between amino acid side chains. For example, glycine, proline, aspargine, and aspartic acid are favored in turns. Non-covalent interactions that stabilize hairpin formation include salt bridges, pi-stacked aromatic interactions, cation-pi interactions, and hydrophobic interactions. The optimal strand length for beta hairpins depends on the numbers of stabilizing non-covalent interactions and high hairpin propensity amino acids in the specific peptide being designed. Until now, de novo hairpins have not previously been used to examine biological processes aside from protein folding. This thesis uses de novo designed biomimetic peptides as tractable models to examine how non-covalent interactions control the redox properties of tyrosine in enzymes. The data in this study demonstrate that proton transfer to histidine, a hydrogen bond to arginine, and a pi-cation interaction create a peptide environment that lowers the midpoint potential of tyrosine in beta hairpins. Moreover, these interactions contribute equally to control the midpoint potential. The data also show that hydrogen bonding is not the sole determinant of the midpoint potential of tyrosine. Finally, the data suggest that the Tyr 160D2-Arg 272CP47 pi-cation interaction contributes to the differences in redox properties between Tyr 160 and Tyr 161 of photosystem II.

Thesis (Ph. D.)--Case Western Reserve University, 2006. / [School of Medicine] Department of Pathology. Includes bibliographical references.

Diss. (sammanfattning) Umeå : Umeå Universitet, 2007. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references (leaves 293-348). Issued in print and online. Available via ProQuest Digital Dissertations.

Thesis (Ph. D.)--West Virginia University, 2004 / Title from document title page. Document formatted into pages; contains vii, 350 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 322-346).

Thesis (Ph. D.)--Case Western Reserve University, 2006. / [School of Medicine] Department of Pathology. Includes bibliographical references. Available online via OhioLINK's ETD Center.

Övervikt och fetma sprider sig likt en epidemi över världen. Omkring 1,9 miljarder vuxna varöverviktiga år 2014 och av dessa klassificerades 600 miljoner som feta. Forskning kring fetmas uppkomst och nya former av behandlingsalternativ pågår. En viktig faktor för uppkomst av övervikt är aptitreglering, där t.ex. Peptide tyrosine tyrosine (PYY), Oxyntomodulin (OXM) och Glucosedependent insulinotropic polypeptide (GIP) har betydelse. En litteraturstudie genomfördes där totalt nio originalartiklar från PubMed utvärderades. Syftet var att undersöka om det finns något värde i att mäta dessa hormon postprandialt. Finns det någon skillnad mellan normalviktiga, överviktiga och obesa och finns det någon skillnad mellan individer med typ 2-diabetes mellitus (T2DM) och friska individer? Finns det någon pålitlig analysmetod? Samtliga studier var måltidsstudier där olika näringsämnens påverkan på den postprandiala responsen undersöktes. Peptide tyrosine tyrosine ochGlucose-dependent insulinotropic polypeptide mättes i sex resp. fem av artiklarna och OXM mättes ien artikel. Protein, fett och kolhydrater ger en postprandial respons på PYY och GIP. Responsen av PYY var starkast efter stimuli från fett och protein. Fett tycks ge starkast respons på GIP. Fastevärden av PYY och GIP var inte olika hos normalviktiga och överviktiga i de studier som undersöktes. Det fanns en signifikant skillnad (p=0,01) mellan normalviktiga och överviktiga tonårsflickor av den postprandiala utsöndringen av PYY efter fettrik måltid, där de obesa flickorna hade lägre procentuell ändring jämfört med de normalviktiga. Pålitliga analysmetoder vid koncentrationsbestämning av dessa tre hormon i plasma är Radioimmunoassay (RIA) och Enzyme-linked immunosorbent assay (ELISA).