Effects of the Fc-III tag on activity and stability of green fluorescent protein and human muscle creatine kinase

Profiling Glutathionylome in CD38-Mediated Epithelial-Mesenchymal Transition

Protein S-glutathionylation is an important posttranslational modification that regulates various cellular processes. However, changes in glutathionylome in epithelial-mesenchymal transition (EMT), a crucial cellular process for embryonic development, wound healing, and carcinoma progression and metastasis, have not been fully characterized. Our previous study revealed that CD38 overexpression decreased cellular nicotinamide adenine dinucleotide (NAD⁺) levels and caused cells to undergo EMT. In the present study, we engineered a cell system in which the glutathione synthetase (GS) mutant was expressed that catalyzed the formation of a glutathione analogue from azido-alanine to profile changes of glutathionylome in CD38-overexpressing cells. We identified 1298 glutathionylated proteins and revealed that proteins with changed glutathionylation levels involved in EMT associated pathways including epithelial adherens junction, actin cytoskeleton, and integrin signaling. Moreover, the glutathionylation level of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) was increased in CD38-overexpressing cells. We further demonstrated that glutathionylation of Cys63 residue in 15-PGDH led to decreased enzymatic activity that could promote EMT by increasing prostaglandin E₂ (PGE₂). Taken together, these results indicate that the clickable glutathione is an effective probe for glutathionylome profiling, and glutathionylation of 15-PGDH on Cys63 inhibits its enzymatic activity to promote EMT.

Characterization of the Fc-III-4C-based recombinant protein expression system by using carbonic anhydrase as the model protein

Development of new affinity tags is important for recombinant protein expression and purification. Based on our earlier work, we devised an affinity tag by addition of two cysteine residues onto the N- and C-termini of the Fc-III peptide and designated as the Fc-III-4C tag, in which four cysteine residues form two disulfide linkages. The binding affinity of Fc-III-4C tag to human IgG is measured as 2.28 nM (K_d) and is 100 times higher than that of the Fc-III tag to IgG. Fc-III-4C tagged carbonic anhydrase (CA) can be effectively purified with IgG-immobilized beads, and Fc-III-4C tag does not possess adverse effects on the structure and stability of CA. Furthermore, the Fc-III-4C tagged protein binds to multiple transition metal ions, which enhances activities of enzymes that use metal ions as co-factors. These results suggest that Fc-III-4C tag is a useful tool for expression and purification of recombinant proteins and enhances the activities of some fusion proteins that use Zn²⁺ or Cu²⁺ as cofactors.

A comprehensive review of the neonatal Fc receptor and its application in drug delivery

Advances in the understanding of neonatal Fc receptor (FcRn) biology and function have demonstrated that this receptor, primarily identified for the transfer of passive immunity from mother infant, is involved in several biological and immunological processes. In fact, FcRn is responsible for the long half-life of IgG and albumin in the serum, by creating an intracellular protein reservoir, which is protected from lysosomal degradation and, importantly, trafficked across the cell. Such discovery has led researchers to hypothesize the role for this unique receptor in the controlled delivery of therapeutic agents. A great amount of FcRn-based strategies are already under extensive investigation, in which FcRn reveals to have profound impact on the biodistribution and half-life extension of therapeutic agents. This review summarizes the main findings on FcRn biology, function and distribution throughout different tissues, together with the main advances on the FcRn-based therapeutic opportunities and model systems, which indicate that this receptor is a potential target for therapeutic regimen modification.

Development of a Clickable Probe for Profiling of Protein Glutathionylation in the Central Cellular Metabolism of E. coli and Drosophila

Protein glutathionylation is an important post-translational modification that regulates many cellular processes, including energy metabolism, signal transduction, and protein homeostasis. Global profiling of glutathionylated proteins (denoted as glutathionylome) is crucial for understanding redox-regulated signal transduction. Here, we developed a novel method based on click reaction and proteomics to enrich and identify the glutathionylated peptides in Escherichia coli and Drosophila lysates, in which 937 and 1,930 potential glutathionylated peptides were identified, respectively. Bioinformatics analysis showed that the cysteine residue next to negatively charged amino acid residues has a higher frequency of glutathionylation. Importantly, we found that most proteins associated with metabolic pathways were glutathionylated and that the glutathionylation sites of metabolic enzymes were highly conserved among different species. Our results indicate that the glutathione analog is a useful tool to characterize protein glutathionylation, and glutathionylation of metabolic enzymes, which play important roles in regulating cellular metabolism, is conserved.

Long-range effects of tag sequence on marginally stabilized structure in HIV-1 p24 capsid protein monitored using NMR

N-terminal domain of HIV-1 p24 capsid protein is a globular fold composed of seven helices and two β-strands with a flexible structure including the α4-5 loop and both N- and C-terminal ends. However, the protein shows a high tendency (48%) for an intrinsically disordered structure based on the PONDR VL-XT prediction from the primary sequence. To assess the possibility of marginally stabilized structure under physiological conditions, the N-terminal domain of p24 was destabilized by the addition of an artificial flexible tag to either N- or C-terminal ends, and it was analyzed using T1, T2, hetero-nuclear NOE, and amide-proton exchange experiments. When the C-terminal tag (12 residues) was attached, the regions of the α3-4 loop and helix 6 as well as the α4-5 loop attained the flexible structures. Furthermore, in the protein containing the N-terminal tag (27 residues), helix 4 in addition to the above-mentioned area including α3-4 and α4-5 loops as well as helix 6 exhibited highly disordered structures. Thus, the long-range effects of the existence of tag sequence was observed in the stepwise manner of the appearance of disordered structures (step 1: α4-5 loop, step 2: α3-4 loop and helix 6, and step 3: helix 4). Furthermore, the disordered regions in tagged proteins were consistent with the PONDR VL-XT disordered prediction. The dynamic structure located in the middle part (α3-4 loop to helix 6) of the protein shown in this study may be related to the assembly of the viral particle.