Effective non-denaturing purification method for improving the solubility of recombinant actin-binding proteins produced by bacterial expression

Sodium Dodecyl Sulfate Analogs as a Potential Molecular Biology Reagent

In this study, we review the properties of three anionic detergents, sodium dodecyl sulfate (SDS), Sarkosyl, and sodium lauroylglutamate (SLG), as they play a critical role in molecular biology research. SDS is widely used in electrophoresis and cell lysis for proteomics. Sarkosyl and, more frequently, SDS are used for the characterization of neuropathological protein fibrils and the solubilization of proteins. Many amyloid fibrils are resistant to SDS or Sarkosyl to different degrees and, thus, can be readily isolated from detergent-sensitive proteins. SLG is milder than the above two detergents and has been used in the solubilization and refolding of proteins isolated from inclusion bodies. Here, we show that both Sarkosyl and SLG have been used for protein refolding, that the effects of SLG on the native protein structure are weaker for SLG, and that SLG readily dissociates from the native proteins. We propose that SLG may be effective in cell lysis for functional proteomics due to no or weaker binding of SLG to the native proteins.

Microscopic studies on severing properties of actin-binding protein: its potential use in therapeutic treatment of actin-rich inclusions

Actin is an important unit of the cytoskeletal system, involved in many cellular processes including cell motility, signaling, and intracellular trafficking. Various studies have been undertaken to understand the regulatory mechanisms pertaining actin functions, especially the ones controlled by actin-binding proteins. However, not much has been explored about the molecular aspects of these proteins implicated in various diseases. In this study, we aimed to demonstrate the molecular properties of gelsolin, an actin-severing protein on the disassembly of the aggregation of actin-rich intracellular inclusions, Hirano body. We observed a decreasing tendency of actin aggregation by co-sedimentation assay and transmission electron microscopy in the presence of gelsolin. Therefore, we provide suggestive evidence for the use of actin-severing protein in novel therapeutic strategies for neurodegenerative conditions.

The actin bundling activity of actin bundling protein 34 is inhibited by calcium binding to the EF2

Actin bundling protein 34 (ABP34) is the one of 11 actin-crosslinking proteins identified in Dictyostelium discoideum, a novel model organism for the study of actin-associated neurodegenerative disorders such as Alzheimer's disease and Huntington's disease. ABP34 localizes at the leading and trailing edges of locomotory cells, i.e., at the cell cortex, filopodia, and pseudopodia. Functionally, it serves to stabilize membrane-associated actin at sites of cell-cell contact. In addition, this small crosslinking protein is involved in actin bundle formation, and its bundling activity is regulated by the concentration of calcium ion. Several studies have sought to determine the mechanism underlying the calcium-regulated actin bundling activity of ABP34, but it remains unclear. Using several mutational and structural analyses, we revealed that calcium binding to the EF2 motif disrupts the inter-domain interaction between the N- and C-domains, thereby inhibiting the actin bundling activity of ABP34. This finding provides clues about the pathogenesis of neurodegenerative disorders related to actin bundling.

Recombinant protein of the first two ectodomains of cadherin 23 from erl mice shows impairment in Ca2+-dependent proteolysis protection

The erl mouse is a mouse model of nonsyndromic autosomal recessive deafness (DFNB12) on the C57BL/6J background. This project was carried out to express the first two ectodomains of cadherin 23 (CDH23 EC1+2) of erl mice in Escherichia coli and identify the Ca²⁺-binding ability of the recombinant protein. DNA sequences of CDH23 EC1+2 from wild type and erl mice were synthesized and cloned into pBV220 plasmids. Recombinant plasmids were transformed into Escherichia coli and expression of CDH23 EC1+2 was induced by increasing the temperature from 30 °C to 42 °C. The proteins were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and antigenicity of proteins was identified by Western Blotting. Inclusion bodies were denatured in 8 M urea, purified by ion-exchange and gel filtration chromatography and refolded with dialysis in buffer containing 0.1% sarkosyl. The Ca²⁺-binding ability of CDH23 EC1+2 was determined by Ca²⁺-dependent proteolysis protection. The results showed that the sizes and sequences of inserts in recombinant plasmids were consistent with expectation and that the recombinant proteins were found mainly in the form of inclusion bodies which maintain antigenicity. After refolding, the secondary structures of recombinant proteins were measured by circular dichroism (CD) spectra. Moreover, CDH23 EC1+2 from the erl mice showed less Ca²⁺-dependent proteolysis protection comparing with that of the wild type control. We therefore concluded that impairment of Ca²⁺-dependent protein interaction was likely involved in the progressive hearing loss in erl mice. The results may aid in understanding the mechanism of hearing loss in DFNB12.