Moorhead, GregoryLabandera, Anne Marie Lyse2017-06-062017-06-0620172017Labandera, A. M. (2017). Identification and Characterization of a Novel Tyrosine Phosphatase in Plants (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26416http://hdl.handle.net/11023/3873The study of tyrosine phosphorylation in plants has been largely neglected due to the lack of classic tyrosine kinases and underrepresentation of tyrosine phosphatases compared to humans. However, advanced phosphoproteomics studies have revealed that the abundance of phospho-tyrosine residues in plants parallels human signal transduction. This strongly suggests that in plants tyrosine phosphorylation is as important as in humans, yet we know nothing about the players responsible for these events. The Arabidopsis thaliana Rhizobiale-like phosphatase 2 (AtRLPH2) is a novel protein phosphatase not found in mammals which, according to bioinformatics analysis, clusters with the serine/threonine-specific phospho-protein phosphatase (PPP) group. In the present work, it is shown that recombinant AtRLPH2 surprisingly behaves like a tyrosine phosphatase in vitro by dephosphorylating phospho-tyrosine peptides and having essentially no activity towards phospho-serine/threonine residues. Furthermore, the endogenous AtRLPH2 from Arabidopsis thaliana was also shown to preferentially dephosphorylate tyrosine phosphorylated peptides and protein. This work shows for the first time that a member of the plant PPP family of phosphatases has the capability to dedicate its activity solely toward phospho-tyrosine. In order to understand the novel substrate specificity of AtRLPH2 its crystal structure was elucidated, providing detailed mechanistic insight into its mode of function and characteristics of its potential substrates. AtRLPH2 possesses a basic pocket next to the active site which makes it imperative for the substrate to possess a phospho-threonine/serine two amino acids upstream the phospho-tyrosine. To gain a better understanding of AtRLPH2 significance and targets, a phosphoproteomics study was undertaken to compare phospho-tyrosine peptides from wild type and atrlph2 knockout plant lines. In summary, the atypical tyrosine phosphatase AtRLPH2 was characterized by a multidisciplinary approach involving biochemistry, cell biology, phosphoproteomics and structural biology.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.BiologyBiochemistryPlant BiologyProtein phosphataseStructural Biologydoctoral thesis10.11575/PRISM/26416