Determination of the arginine content of proteins by the Sakaguchi procedure

An injectable self-assembling hydrogel based on RGD peptidomimetic β-sheets as multifunctional biomaterials

Ability of the cells to adhere to an extracellular material is central to successful tissue genesis. Arg-Gly-Asp (RGD) sequences found in extracellular matrix proteins are well known for cell adhesion, however, enzymatic degradation and lack of specificity have limited their widespread use. Besides, a multifunctional material with inherent antimicrobial ability would help in invigorating the practical tissue engineering applications. Here, we report novel modified RGD (M_R) and RGD mimic [R(K)] peptides (M_OH and M_NH2) which were synthesized post-in-silico screening, based on their interactions with integrin protein α_Vβ₃ using HEX 8.0 docking server. These mimics, containing hydrophobic Phe-Phe (FF) moiety which has been specifically introduced to initiate the self-assembling process of β-sheet structures, were characterized thoroughly using various physicochemical and spectroscopic techniques. Under physiological conditions, these mimetics displayed thixotropic behavior rendering them highly suitable as injectable hydrogels having an added advantage of site-specific targeting abilities. Electron microscopy further revealed the formation of nanofibers upon self-assembly of these peptides. Besides, enhanced cell adhesiveness by these peptides compared to the commercial Poly l-lysine coated surfaces as well as the inherent antimicrobial potential against both sensitive and antibiotic-resistant pathogens (Methicillin-resistant Staphylococcus aureus and multi-drug resistant Salmonella enteritidis) substantiated the applicability of these unique injectable hydrogels wherein the porous fibrous framework offered a favorable environment for drug entrapment and 3D cell culture. Altogether, these properties render these novel RGD mimic peptides as promising multifunctional candidates for various tissue regenerative applications.

Arginine induces protein self-assembly into nanofibers for triggering osteogenic differentiation of stem cells

Although silk proteins are considered promising in building a scaffold for tissue engineering, one of the silk proteins, Bombyx mori silk sericin (BS), has limited processability in producing nanofibrous scaffolds because its surface charge anisotropy promotes gelation instead. To overcome this daunting challenge, we developed a mild and simple procedure for assembling BS into nanofibers and nanofibrous scaffolds. Briefly, arginine was added to the aqueous BS solution to reduce the negative charge of BS, thereby inducing BS to self-assemble into nanofibers in the solution. Circular dichroism (CD) and Fourier transform infrared (FT-IR) spectra showed that arginine promoted the formation of β-sheet conformation in BS and increased its thermal stability. Furthermore, the arginine-induced BS nanofiber solution could be casted into scaffolds made of abundant network-like nanofibrous structures. The BS scaffolds promoted cell adhesion and growth and stimulated osteogenic differentiation of the bone marrow mesenchymal stem cells (BMSCs) in the absence of differentiation inducers in culture media. Our study presents a new strategy for assembling proteins into osteogenic nanofibrous scaffolds for inducing stem cell differentiation in regenerative medicine.

Photoresponsive amphiphilic azobenzene–PEG self-assembles to form supramolecular nanostructures for drug delivery applications

Self-assembled smart nanostructures have emerged as controlled and site-specific systems for drug delivery applications.

Heat-induced changes in sodium Caseinate

Chemical and physical changes that occur in Na caseinate (at 1 or 2% in water, pH 7·0) on heating in the range 120–150 °C were investigated by polyacrylamide gel electrophoresis, ion-exchange and gel-permeation chromatography, light scattering, u.v. spectroscopy, amino acid analysis, and the formation of pH 4·6 and 12% TCA-soluble N and 12% TCA-soluble P. The electropherograms of heated samples were smeared and indistinct suggesting intermolecular aggregation which was not reversed by 6 M-urea or SDS and indicating covalent bond formation; αs2-casein was especially sensitive. Aggregation was confirmed by ion-exchange chromatography and light scattering. Fragmentation of the caseins also occurred on heating, as indicated by the formation of pH 4·6 and 12% TCA-soluble N and by gel filtration. Formation of soluble N and dephosphorylation followed first-order kinetics. Concentrations of available lysine and available methionine were reduced by 10–15% on heating at 140 °C for 30min; chemical assays for arginine and tryptophan indicated increases, suggesting interference. Ultraviolet spectroscopy indicated a slight apparent increase in aromatic residues after heating at 140 °C for up to 60 min.

The acceleration by cationic materials of the coagulation of casein micelles by rennet

Three cationic materials markedly reduced the rennet clotting time of casein micelle suspensions, the efficacy of each being primarily dependent on the charge and the amount absorbed by the micelles. The reduction in coagulation time was unaffected by components of the milk serum other than salts. No enzymic action by lysozyme on casein micelles was detected. All materials acted by the same mechanism, increasing the affinity of rennet for the micelles and accelerating the aggregation phase. Coagulation did not occur until a minimum amount of κ-casein had been hydrolysed to para-κ-casein. All additives increased the proportion of added rennet retained by the casein in the coagulum. The results indicated that coagulation occurs by specific interactions between micelles modified by rennet.

Chemical conjugation of ΔF508-CFTR corrector deoxyspergualin to transporter human serum albumin enhances its ability to rescue Cl−channel functions

The most common mutation of the cystic fibrosis (CF) gene, the deletion of Phe508, encodes a protein (ΔF508-CFTR) that fails to fold properly, thus mutated ΔF508-cystic fibrosis transmembrane conductance regulator (CFTR) is recognized and degraded via the ubiquitin-proteasome endoplasmic reticulum-associated degradation pathway. Chemical and pharmacological chaperones and ligand-induced transport open options for designing specific drugs to control protein (mis)folding or transport. A class of compounds that has been proposed as having potential utility in ΔF508-CFTR is that which targets the molecular chaperone and proteasome systems. In this study, we have selected deoxyspergualin (DSG) as a reference molecule for this class of compounds and for ease of cross-linking to human serum albumin (HSA) as a protein transporter. Chemical cross-linking of DSG to HSA via a disulfide-based cross-linker and its administration to cells carrying ΔF508-CFTR resulted in a greater enhancement of ΔF508-CFTR function than when free DSG was used. Function of the selenium-dependent oxidoreductase system was required to allow intracellular activation of HSA-DSG conjugates. The principle that carrier proteins can deliver pharmacological chaperones to cells leading to correction of defective CFTR functions is therefore proven and warrants further investigations.

Use of inducible feedback-resistant N-acetylglutamate synthetase (argA) genes for enhanced arginine biosynthesis by genetically engineered Escherichia coli K-12 strains

The goal of this work was to construct Escherichia coli strains capable of enhanced arginine production. The arginine biosynthetic capacity of previously engineered E. coli strains with a derepressed arginine regulon was limited by the availability of endogenous ornithine (M. Tuchman, B. S. Rajagopal, M. T. McCann, and M. H. Malamy, Appl. Environ. Microbiol. 63:33-38, 1997). Ornithine biosynthesis is limited due to feedback inhibition by arginine of N-acetylglutamate synthetase (NAGS), the product of the argA gene and the first enzyme in the pathway of arginine biosynthesis in E. coli. To circumvent this inhibition, the argA genes from E. coli mutants with feedback-resistant (fbr) NAGS were cloned into plasmids that contain "arg boxes," which titrate the ArgR repressor protein, with or without the E. coli carAB genes encoding carbamyl phosphate synthetase and the argI gene for ornithine transcarbamylase. The free arginine production rates of "arg-derepressed" E. coli cells overexpressing plasmid-encoded carAB, argI, and fbr argA genes were 3- to 15-fold higher than that of an equivalent system overexpressing feedback-sensitive wild-type (wt) argA. The expression system with fbr argA produced 7- to 35-fold more arginine than a system overexpressing carAB and argI genes on a plasmid in a strain with a wt argA gene on the chromosome. The arginine biosynthetic capacity of arg-derepressed DH5 alpha strains with plasmids containing only the fbr argA gene was similar to that of cells with plasmids also containing the carAB and argI genes. Plasmids containing wt or fbr argA were stably maintained under normal growth conditions for at least 18 generations. DNA sequencing identified different point mutations in each of the fbr argA mutants, specifically H15Y, Y19C, S54N, R58H, G287S, and Q432R.

Synthesis of active nitroguaiacol ether derivatives of streptomycin

The synthesis, purification, and biological properties of nitroguaiacol ether derivatives of streptomycin and their corresponding radioactive reduced products were examined. These derivatives are biologically active against gram-positive and gram-negative eubacteria and they are also photoreactive because of the presence of the nitroguaiacol group in the molecule. We demonstrated that these derivatives can be used as streptomycin analogs in photoaffinity labeling of the macromolecular structures related to the mode of action of the antibiotic.

Quantitative determination of monosubstituted guanidines: a comparative study of different procedures

Analysis of N2-acyl arginine derivatives as well as of arginine analogs lacking in alpha-amino function by Weber's modification of the Sakaguchi procedure yielded colored complexes with absorbance values approximately twice that obtained with an equivalent concentration of unmodified arginine. The limitations concerning the applicability of the various modifications of the Sakaguchi procedure as well as of the fluorimetric assay to the quantitative estimation of a variety of monosubstituted guanidines and proteins are discussed.

Preparation and conformational study of clupeine fragments

Fragments of clupeines, YI, YII, and Z of divergent chain length and different amino acid composition were prepared by digestion with thermolysin and a mixture of carboxypeptidases A and B, and their conformational preferences examined as a function of pH, added salts, presence of a helix-supporting solvent, and temperature. All these highly basic oligopeptides adopt an essentially unordered conformation in aqueous solution. 2-Chloroethanol supports in various amounts the onset of the right-handed alpha-helical form in the carboxy-peptidase fragments.

Protamines. II. Circular dichroism study of the three main components of clupeine

The three main components YI, YII, and Z of clupeine, a protamine from herring, have been purified and characterized. The conformational preferences of clupeines have been examined as a funciton of pH, temperature, added salts, and presence of structure-disrupting agents and helix-supporting solvents using circular dichroism. It was found that these small basic proteins assume predominantly an unordered conformation in aqueous solution. Addition of counter ions, in particular perchlorate, and 2-chloroethanol induces in various amounts the onset of the right-handed alpha-helical conformation. Urea favors the statistical coil state. It was also demonstrated that in the 0.1--4.0 . 10(-1) M range, in contrast to clupeines YI and Z, the circular dichroic properties of the YII component do not seem to be sensitive to the addition of mono- and diphosphate.

Metal ion-induced conformational changes in Escherichia coli alkaline phosphatase

Ultraviolet difference spectra are produced by the binding of divalent metal ions to metal-free alkaline phosphatase (EC 3.1.3.1). The interaction of the apoprotein with Zn2+, Mn2+, Co2+ and Cd2+, which induce the tight binding of one phosphate ion per dimer, give distinctly different ultraviolet spectra changes from Ni2+ and Hg2+ which do not induce phosphate binding. Spectrophotometric titrations at alkaline pH of various metallo-enzymes reveal a smaller number of ionizable tyrosines and a greater stability towards alkaline denaturation in the Zn2+- and Mn2+-enzymes than in the Ni2+-, Hg2+- and apoenzymes. The Zn2+- and Mn2+-enzymes have CD spectra in the region of the aromatic transitions that are different from the CD spectra of the Ni2+-, Hg2+- and apoenzymes. Modifications of arginines with 2,3-butanedione show that a smaller number of arginine residues are modified in the Zn2+-enzyme than in the Hg2+-enzyme. The presented data indicate that alkaline phosphatase from Escherichia coli must have a well-defined conformation in order to bind phosphate. Some metal ions (i.e. Zn2+, Co2+, Mn2+ and Cd2+), when interacting with the apoenzyme, alter the conformation of the protein molecule in such a way that it is able to interact with substrate molecules, while other metal ions (i.e. Ni2+ and Hg2+) are incapable of inducing the appropriate conformational change of the apoenzyme. These findings suggest an important structural function of the first two tightly bound metal ions in enzyme.

Identification of components of the streptomycin-binding center of E. coli MRE 600 ribosomes by photo-affinity labelling

The [H3]-labelled photo-activated analog of streptomycin (photo-Sm) is obtained as a result of the streptomycin reaction with 2-nitro, 4-azidobenzoylhydrazide and subsequent reduction with NaBH34. The analog retains the functional activity of the initial antibiotic as judged by two criteria: (1) it binds only to the 30S subparticle of ribosomes and (2) it inhibits the factor-free ("non-enzymatic") PCMB-stimulated polyU-dependent system of translation (Gavrilova and Spirin, 1971). After irradiation of the reaction mixture containing photo-Sm and either the 30S or 50S subparticles of ribosomes under similar conditions, the analog covalently binds chiefly to the 30S subparticle. Irradiation of the photo-Sm mixture with whole 70S ribosomes leads to a uniform distribution of a covalently bound label among the subparticles. A comparison of the effects obtained allows the conclusion that the analog is located on the interface of the ribosomal subparticles. In the 30S subparticle the photo-Sm attacks mainly the protein component (more than 95% of all the covalently bound label). The proteins labelled by photo-reaction are identified as S7 (main), S14 (additional) and S16/S17 (minor).