c-Src kinase activity is regulated by phosphorylation of Y527 and Y416. Y527 phosphorylation stabilizes a closed conformation, which suppresses kinase activity towards substrates, whereas phosphorylation at Y416 promotes an elevated kinase activity by stabilizing the activation loop in a manner permissive for substrate binding. Here we investigated the correlation of Y416 phosphorylation with c-Src activity when c-Src was locked into the open and closed conformations (by mutations Y527F and Q528E, P529E, G530I respectively). Consistent with prior findings, we found Y416 to be more greatly phosphorylated when c-Src was in an open, active conformation. However, we also observed an appreciable amount of Y416 was phosphorylated when c-Src was in a closed, repressed conformation under conditions by which c-Src was unable to phosphorylate substrate STAT3. The phosphorylation of Y416 in the closed conformation arose by autophosphorylation, since abolishing kinase activity by mutating the ATP binding site (K295M) prevented phosphorylation. Basal Y416 phosphorylation correlated positively with cellular levels of c-Src suggesting autophosphorylation depended on self-association. Using sedimentation velocity analysis on cell lysate with fluorescence detection optics, we confirmed that c-Src forms monomers and dimers, with the open conformation also forming a minor population of larger mass complexes. Collectively, our studies suggest a model by which dimerization of c-Src primes c-Src via Y416 phosphorylation to enable rapid potentiation of activity when Src adopts an open conformation. Once in the open conformation, c-Src can amplify the response by recruiting and phosphorylating substrates such as STAT3 and increasing the extent of autophosphorylation.

Src is critical to both neuronal survival and death. Intact Src sustains neuronal survival. However, in the excitotoxic condition, calpain cleavage of Src generates a neurotoxic truncated Src fragment. Both intact Src and the neurotoxic truncated Src fragment exert their biological actions by controlling the activities of neuroprotective protein kinases.

We developed a new approach to distinguish distinct protein conformations in live cells. The method, exposable tetracysteine (XTC), involved placing an engineered tetracysteine motif into a target protein that has conditional access to biarsenical dye binding by conformational state. XTC was used to distinguish open and closed regulatory conformations of Src family kinases. Substituting just four residues with cysteines in the conserved SH2 domain of three Src-family kinases (c-Src, Lck, Lyn) enabled open and closed conformations to be monitored on the basis of binding differences to biarsenical dyes FlAsH or ReAsH. Fusion of the kinases with a fluorescent protein tracked the kinase presence, and the XTC approach enabled simultaneous assessment of regulatory state. The c-Src XTC biosensor was applied in a boutique screen of kinase inhibitors, which revealed six compounds to induce conformational closure. The XTC approach demonstrates new potential for assays targeting conformational changes in key proteins in disease and biology.

Fluorescent proteins and dyes are essential tools for the study of protein trafficking, localization and function in cells. While fluorescent proteins such as green fluorescence protein (GFP) have been extensively used as fusion partners to proteins to track the properties of a protein of interest 1 , recent developments with smaller tags enable new functionalities of proteins to be examined in cells such as conformational change and protein-association 2, 3 . One small tag system involves a tetracysteine motif (CCXXCC) genetically inserted into a target protein, which binds to biarsenical dyes, ReAsH (red fluorescent) and FlAsH (green fluorescent), with high specificity even in live cells 2 . The TC/biarsenical dye system offers far less steric constraints to the host protein than fluorescent proteins which has enabled several new approaches to measure conformational change and protein-protein interactions 4-7 . We recently developed a novel application of TC tags as sensors of oligomerization in cells expressing mutant huntingtin, which when mutated aggregates in neurons in Huntington disease 7 . Huntingtin was tagged with two fluorescent dyes, one a fluorescent protein to track protein location, and the second a TC tag which only binds biarsenical dyes in monomers. Hence, changes in colocalization between protein and biarsenical dye reactivity enabled submicroscopic oligomer content to be spatially mapped within cells. Here, we describe how to label TC-tagged proteins fused to a fluorescent protein (Cherry, GFP or CFP) with FlAsH or ReAsH in live mammalian cells and how to quantify the two color fluorescence (Cherry/FlAsH, CFP/FlAsH or GFP/ReAsH combinations).

Objective: Preeclampsia (PE) is a complex pregnancy-specific disorder characterized by the onset of hypertension and proteinuria in the second trimester of pregnancy. The pathogenesis of PE still remains unknown. Revealing the specific proteins involved in placental functions is important for a better understanding of the pathogenesis of PE. In this study, we aimed to investigate the expression levels of E-cadherin, endothelin-1, and CD68 in both preeclamptic and normal placentas. Materials and Methods:In this study, placentas after birth at 35-38 weeks were included. Ten preeclamptic placentas and 10 normal placentas were used. The expression levels of E-cadherin, endothelin-1, and CD68 were measured by western blot.Results: It was observed that the expression of E-cadherin and endothelin-1 was not at detectable levels in normal placentas; however, E-cadherin and endothelin-1 were observed to be highly expressed in preeclamptic placentas. In addition, the expression of CD68 was found to be markedly increased in preeclamptic placentas in comparison to control placentas. Conclusion:The increased expression of E-cadherin, endothelin-1, and CD68 may play an important role in impaired trophoblast invasion, endothelial dysfunction, and inadequate spiral remodeling, which are key factors involved in the pathogenesis of PE.