Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)




Shantá D Hinton

Committee Member

Lizabeth A Allison

Committee Member

Mark H Forsyth


The intriguing protein MK-STYX [MAPK (mitogen-activated protein kinase) phospho-serine/threonine/tyrosine-binding protein] has been receiving attention because recent work has implicated it in a number of biological processes. MK-STYX is a pseudophosphatase involved in cellular stress responses, neuronal differentiation, apoptosis, and several cancers. As a pseudophosphatase, it is catalytically inactive due to mutations in its enzyme active site. However, it retains structural domains that enable it to perform protein-protein interactions. It is important to consider how exactly MK-STYX may carry out its many functions. Another multifunctional protein, known as GSK3 (glycogen synthase kinase 3) has some overlapping functions with MK-STYX so it is exciting to consider that MK-STYX may impact GSK3 to exert its cellular functions. GSK3 refers to two paralogous and homologous enzymes known as GSK3 and GSK3. These are regulated by inhibitory phosphorylation on serine 21/9 and activating phosphorylation on tyrosine 279/216 for GSK3/, respectively. Accordingly, biochemical studies were carried out to determine whether MK-STYX changed the phosphorylation at these sites, or indeed if MK-STYX changed the amount of GSK3. A multifunctional kinase like GSK3 has many physiological roles, so if MK-STYX changes regulatory phosphorylation sites or protein expression of GSK3, it was hypothesized that MK-STYX could affect GSK3 functions, and that additionally, MK-STYX could form a protein complex with GSK3 and then modulate it. Western blot analysis revealed that MK-STYX decreased serine 9 phosphorylation on GSK3, suggesting that MK-STYX activates GSK3. MK-STYX did not change serine 21 phosphorylation on GSK3. Also, MK-STYX did not affect total expression of GSK3/. Further, there was no detected interaction between MK-STYX and GSK3 as indicated by coimmunoprecipitation. Overall, this thesis suggests MK-STYX may have some regulatory role over GSK3. Further biochemical work should clarify this connection and its biological significance.



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