Longer charged amino acids favor ß-strand formation in hairpin peptides.

Interactions between charged amino acids significantly influence the structure and function of proteins. The encoded charged amino acids Asp, Glu, Arg, and Lys have different number of hydrophobic methylenes linking the backbone to the charged functionality. It remains to be fully understood how does this difference in the number of methylenes affect protein structure stability. Protein secondary structures are the fundamental three-dimensional building blocks of protein structures. ß-Sheet structures are particularly interesting, because these structures have been associated with a number of protein misfolding diseases. Herein, we report the effect of charged amino acid side chain length at two ß-strand positions individually on the stability of a ß-hairpin. The charged amino acids include side chains with a carboxylate, an ammonium, or a guanidinium group. The experimental peptides, fully folded reference peptides, and fully unfolded reference peptides were synthesized by solid phase peptide synthesis and analyzed by 2D NMR methods including TOCSY, DQF-COSY, and ROESY. Sequence specific assignments were performed for all peptides. The chemical shift data were used to derive the fraction folded population and the folding free energy for the experimental peptides. Results showed that the fraction folded population increased with increasing charged amino acid side chain length. These results should be useful for developing functional peptides that adopt the ß-conformation.

Chemical and Colloidal Dynamics of MnO2 Nanosheets in Biological Media Relevant for Nanosafety Assessment.

Many layered crystal phases can be exfoliated or assembled into ultrathin 2D nanosheets with novel properties not achievable by particulate or fibrous nanoforms. Among these 2D materials are manganese dioxide (MnO2 ) nanosheets, which have applications in batteries, catalysts, and biomedical probes. A novel feature of MnO2 is its sensitivity to chemical reduction leading to dissolution and Mn2+ release. Biodissolution is critical for nanosafety assessment of 2D materials, but the timing and location of MnO2 biodissolution in environmental or occupational exposure scenarios are poorly understood. This work investigates the chemical and colloidal dynamics of MnO2 nanosheets in biological media for environmental and human health risk assessment. MnO2 nanosheets are insoluble in most aqueous phases, but react with strong and weak reducing agents in biological fluid environments. In vitro, reductive dissolution can be slow enough in cell culture media for MnO2 internalization by cells in the form of intact nanosheets, which localize in vacuoles, react to deplete intracellular glutathione, and induce cytotoxicity that is likely mediated by intracellular Mn2+ release. The results are used to classify MnO2 nanosheets within a new hazard screening framework for 2D materials, and the implications of MnO2 transformations for nanotoxicity testing and nanosafety assessment are discussed.

Development and clinical applications of glasses-free three-dimensional (3D) display technology for thoracoscopic surgery.

The conventional two-dimensional (2D) and glasses-assisted three-dimensional (3D) display systems can no longer meet the clinical requirements with the development of minimally invasive video-assisted thoracoscopic surgery (VATS). The glasses-free 3D display technology adopts both lenticular lens technology and face-tracking and -positioning systems and offers high brightness, large viewing area, and strong anti-interference capability, which significantly improve the operator's experience. When applied in VATS, it has many advantages including good display depth, convenience for performing complex and fine operations, and short learning curve. This novel display technology will greatly promote the development of minimally invasive surgery.

Effect of lysine methylation and acetylation on the RNA recognition and cellular uptake of Tat-derived peptides.

The two lysine (Lys) residues in the human immunodeficiency virus trans-activator of transcription protein (HIV Tat protein) basic region (residues 47-57) are crucial for two bioactivities: RNA recognition and cellular uptake. Since the post-translational modifications of these two Lys residues affect the biological function of the Tat protein, we investigated the effect of methylation and acetylation of Lys50 and Lys51 in Tat-derived peptides on the two bioactivities. Tat-derived peptides, in which each lysine was replaced with a methylated- or acetylated-Lys, were synthesized by solid phase peptide synthesis. TAR RNA recognition of the peptides was studied by electrophoretic mobility shift assays. Cellular uptake of the peptides into Jurkat cells was determined by flow cytometry. Our results showed that acetylation of either Lys residue attenuated both bioactivities. In contrast, the effect of Lys methylation on the bioactivities depended on position and number of methyl groups. These findings should be useful for the development of functional molecules containing ammonium groups for RNA recognition to affect biological processes and for cellular uptake for drug delivery.