RESUMEN
Protein drugs play an extremely important role in the prevention and treatment of diseases. But the properties of macromolecules hinder their effects on intracellular targets. Among the existing delivery strategies, penetrating peptides are more suitable for clinical research and treatment, and have gradually become the most important tool to deliver protein drugs. Therefore, the development of safe and effective penetrating peptide delivery vehicles is of great significance to the basic research and clinical application of biomedicine. In this paper, a self-releasing intracellular transporter LCA2 based on the enterotoxin A2 domain is designed. This carrier is composed of three parts: a linker, self-releasing enzyme sensitive sites (Cs), and the transmembrane domain LTA2. The fluorescent protein mCherry was used as the model protein to detect the properties of LCA2. The results of electrophoresis showed that the high-purity mCherryLCA2 fusion protein was obtained from the engineered bacteria containing pET24a(+)-ma2 recombinant plasmids, and mCherry could be effectively separated from LCA2 by low concentration trypsin. It was observed under a fluorescence microscope that LCA2 could transport mCherry into different types of cells. Flow cytometry has detected that the transport capacity of LCA2 has certain cellular differences. Confocal microscope fluorescence analysis and Western blotting results showed that the mCherry was transported to the endoplasmic reticulum by the LCA2 carrier, separated from LCA2 by cleavage of enzyme sensitive sites and released into the cell. The CCK-8 results showed that there was no significant change in cell viability within the dose range of 5-40 μg/ mL. These results demonstrate that LCA2 is a safe and effective self-releasing delivery vehicle, which can transport and release active proteins or protein drugs into cells.
RESUMEN
Objective To investigate the effect of calcium on the stability of VWF-A2 domain. Methods The crystal structures of A2 (not containing calcium) and A2/Ca2+ (with calcium bound) were downloaded from protein data bank. For A2 domain, the conformational changes, unfolding pathway differences and the exposure degree variance of cleavage sites caused by calcium binding were observed and analyzed by steered Molecular Dynamics simulations under constant force. Results The unfolding pathway of A2 domain and exposure process of cleavage sites were force-dependent. Calcium binding did not affect the unfolding process of A2 in the early stage. As the conformational rearrangement of α3β4-loop reduced its localized dynamic properties, the movement among β1-β4-β5 strands was restrained, which suppressed its further unfolding to stay in the intermediate steady state and delayed the cleavage-site exposure. Conclusions Stretch force could induce β5 strand of A2 unfolding and the cleavage-site exposure, while calcium binding inhibited ADAMTS13 proteolysis efficiency through stabilizing A2 hydrophobic core and covering its cleavage sites. These results way help to understand how ADAMTS13 cleavages the VWF-A2 domain and regulates the hemostatic potential of VWF, and further provide useful guidance on the design of related anti-thrombus drugs.