ABSTRACT
To improve the mechanical and antibacterial properties of traditional starch-based film, herein, cellulose nanocrystals (CNCs) and chitosan nanoparticles (CS NPs) were introduced to potato starch (PS, film-forming matrix) for the preparation of nanocomposite film without incorporation of additional antibacterial agents. CNCs with varied concentrations were added to PS and CS NPs composite system to evaluate the optimal film performance. The results showed that tensile strength (TS) of nanocomposite film with 0, 0.01, 0.05, and 0.1% (w/w) CNCs incorporation were 41, 46, 47 and 41 MPa, respectively. The elongation at break (EAB) reached 12.5, 10.2, 7.1 and 13.3%, respectively. Due to the reinforcing effect of CNCs, surface morphology and structural properties of nanocomposite film were altered. TGA analysis confirmed the existence of hydrogen bondings and electrostatic attractions between components in the film-forming matrix. The prepared nanocomposite films showed good antibacterial properties against both E. coli and S. aureus. The nanocomposite film, consist of three most abundant biodegradable polymers, could potentially serve as antibacterial packaging films with strong mechanical properties for food and allied industries.
Subject(s)
Chitosan , Nanocomposites , Nanoparticles , Cellulose/chemistry , Chitosan/pharmacology , Chitosan/chemistry , Staphylococcus aureus , Starch/pharmacology , Escherichia coli , Nanoparticles/chemistry , Nanocomposites/chemistry , Anti-Bacterial Agents/pharmacology , Anti-Bacterial Agents/chemistry , Food PackagingABSTRACT
In this paper, ultrafiltration was employed to facilitate the isolation of intermediates in native chemical ligation. Depending on the molecular weight cutoff of the membrane used, molecules with different sizes could be purified, separated, or concentrated by the ultrafiltration process. Total chemical synthesis of the polypeptide chain of the enzyme Sortase AΔN59 was used as an example of the application of ultrafiltration in chemical protein synthesis. Sortase A is a ligase that catalyzes transpeptidation reactions between proteins that have C-terminal LPXTG recognition sequence and Gly5- on the peptidoglycan of bacterial cell walls. Ultrafiltration technique facilitated synthesis of Sortase AΔN59 and was a promising tool in isolation of intermediates in native chemical ligation.
Subject(s)
Aminoacyltransferases/chemical synthesis , Bacterial Proteins/chemical synthesis , Cysteine Endopeptidases/chemical synthesis , Peptides/chemical synthesis , Ultrafiltration/methodsABSTRACT
The enzyme sortaseâ A is a ligase which catalyzes transpeptidation reactions.1, 2 Surface proteins, including virulence factors, that have a C terminal recognition sequence are attached to Gly5 on the peptidoglycan of bacterial cell walls by sortaseâ A.1 The enzyme is an important anti-virulence and anti-infective drug target for resistant strains of Gram-positive bacteria.2 In addition, because sortaseâ A enables the splicing of polypeptide chains, the transpeptidation reaction catalyzed by sortaseâ A is a potentially valuable tool for protein science.3 Here we describe the total chemical synthesis of enzymatically active sortaseâ A. The target 148 residue polypeptide chain of sortaseâ AΔN59 was synthesized by the convergent chemical ligation of four unprotected synthetic peptide segments. The folded protein molecule was isolated by size-exclusion chromatography and had full enzymatic activity in a transpeptidation assay. Total synthesis of sortaseâ A will enable more sophisticated engineering of this important enzyme molecule.
Subject(s)
Aminoacyltransferases/chemical synthesis , Aminoacyltransferases/metabolism , Bacterial Proteins/chemical synthesis , Bacterial Proteins/metabolism , Cysteine Endopeptidases/chemical synthesis , Cysteine Endopeptidases/metabolism , Peptide Fragments/chemistry , Peptide Fragments/metabolism , Amino Acid Sequence , Catalysis , Chromatography, Gel , Molecular Sequence Data , Protein Folding , Spectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationABSTRACT
Well-characterized resins of high purity are critical for effective solid phase peptide synthesis (SPPS). The quality of commercial (4-methyl)benzhydrylamine-resin (MBHA-resin), used for the synthesis of peptide amides, is not consistent and residual ketone functionalities are frequently present. Such ketone or aldehyde impurities lead to the formation of acylation-resistant deletion peptides in SPPS. To avoid these undesirable side reactions, we have optimized the preparation of two amide-generating linkers, which, in combination with aminomethyl-resin prepared directly from polystyrene resin, serve as alternatives to MBHA-resin for peptide amide synthesis. Then we have explored their comparative properties in SPPS. Use of sonication in reductive amination facilitated the synthesis of both benzhydrylamine (BHA) and MBHA linkers.