Preferred Conditions for SrtA Transpeptidation for Creating a DDS Tool

Background/Aim: This study aimed to determine the preferred conditions for the transpeptidase reaction of sortase A from Staphylococcus aureus, for the purpose of creating functional liposomes useful for a drug-delivery system (DDS). Materials and Methods: His-tagged recombinant sortase A with 59 amino acids deleted from the N-terminus (His-ΔN59SrtA) was prepared using an Escherichia coli expression system. The pH dependency and sorting signal sequence dependency of the transpeptidase reaction of His-ΔN59SrtA were analyzed by monitoring the transfer of model donor-substrates (i.e. His-tagged mutant green fluorescent proteins with a C-terminal LPxTG sorting signal) to model acceptor-beads with a GGGGGC peptide. In addition, using preferred conditions, the sortase A reaction was used to modify liposome surface. Results and Discussion: The transpeptidase reaction of His-ΔN59SrtA was enhanced under weakly acidic conditions. Transfer efficiency, based on sorting signal recognition by His-ΔN59SrtA, was similar to or higher than that obtained using several substrates with amino acids other than Glu in the sorting signal position “x”. Furthermore, liposomes containing GGGGGC peptide-linked dipalmitoylphosphatidylethanolamine were successfully modified using the preferred conditions for His-ΔN59SrtA determined in this study. Conclusion: Preferred conditions for the transpeptidase reaction of His-ΔN59SrtA, especially in a weakly acidic environment to enhance reaction, was established and successfully used to create functional liposomes applicable to DDS

Application of Pore-forming Toxin as a DDS Tool

Background/Aim: Cholesterol-dependent cytolysins (CDCs) are pore-forming toxins from Gram-positive bacteria. The aim of this study was to investigate the potential of a CDC, intermedilysin, as a drug-delivery system (DDS) for clinical application. Materials and Methods: Intermedilysin was modified by the addition of a disulfide bridge to regulate pore formation, by swapping domain 4 to provide cholesterol-binding capacity, and by the introduction of a targeting domain. The resultant chimera protein, His-LTBP-CDC(ss)IP, was investigated for its use as a DDS tool in vitro. Results: His-LTBP-CDC(ss)IP exhibited a regulated pore-forming capacity under reducing conditions. This chimera protein was able to deliver a drug-carrier liposome specifically to the target cell, to be endocytosed into the cell with subsequent release of the components into the cytoplasm. Conclusion: A chimera protein derived from the bacterial pore-forming toxin intermedilysin (His-LTBP-CDC(ss)IP) forms the basis for a novel DDS tool

An Improved DDS Tool with Versatile Cell-targeting Ability

Background/Aim: The aim of this study was to develop an improved drug delivery system (DDS) tool with enhanced versatility in the cell-targeting step using as Z-domain, a modified IgG binding domain of protein A from Staphylococcus aureus, as an IgG adapter domain. Materials and Methods: The chimera protein expression system composed of the Z-domain and chimeric cholesterol-dependent cytolysin mutant named His-Z-CDC(ss)IS was constructed in Escherichia coli. His-Z-CDC(ss)IS was purified by Ni-affinity chromatography, and its abilities for controlled pore formation, membrane binding, IgG binding, and target cell-specific delivery of liposomes carrying medicine were investigated. Results and Discussion: His-Z-CDC(ss)IS purified by Ni-affinity chromatography indicated pore-forming activity only under disulfide bond reducing conditions. His-Z-CDC(ss)IS also demonstrated an ability to bind both IgG and cholesterol-embedded liposomes via its Z-domain and domain 4, respectively. Furthermore, anticarcinoembryonic antigen (CEA) IgG-bound His-Z-CDC(ss)IS indicated effective delivery of liposomes carrying drugs to CEA-expressing cells. Conclusion: His-Z-CDC(ss)IS was revealed to be an improved DDS tool with enhanced versatility in cell targeting

Development of SrtA-mediated Peptide-labeled Liposome

Background/Aim: In order to develop an efficient drug-delivery system (DDS), a lipopeptide-loaded liposome that functions as a platform for the transpeptidase reaction mediated by sortase A (SrtA) was constructed and its stability, as well as cell-specific targeting were evaluated in the present study. Materials and Methods: Several lipopeptides possessing an acceptor peptide sequence (oligoglycine ≥ three residues) or donor peptide sequence (LPETG) for the SrtA-mediated reaction were chemically synthesized and then inserted into the liposome membrane composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol (DPPC-Chol-lipo) to obtain the lipopeptide-loaded liposomes. The transpeptidase reaction mediated by recombinant SrtA (His-ΔN59SrtA) was employed to modify the peptide moiety on the liposomal surface using a fluorescently-labeled substrate peptide corresponding to the species of each loaded lipopeptide. Furthermore, lung tumor-binding peptide (LTBP)-labeled liposomes, prepared by this transpeptidase reaction, were investigated for selective targeting to lung cancer cells in vitro. Results and Discussion: The His-ΔN59SrtA-mediated transpeptidation of fluorescently-labeled peptide on the lipopeptide-loaded DPPC-Chol-lipo was confirmed. The selective targeting of LTBP-labeled liposomes to the lung cancer cell line A549 was also observed in vitro. These results suggest that the labeling of acceptor or donor lipopeptide-loaded liposomes with the transpeptidase SrtA could be a useful method for developing a platform applicable to a cancer-targeting DDS