Use of thiazolidine-mediated ligation for site specific biotinylation of mouse EGF for biosensor immobilisation

Biosensors provide a sophisticated and discriminating means of probing biomolecular interactions. Specific ligands such as peptides and proteins can be immobilized onto sensor surfaces by a number of means including covalent attachment via amine, thiol or aldehyde chemistry, capture via biotin-avidin interaction or the use of specific tags. We have devised a simple chemoselective ligation method to selectively conjugate an anchoring functionality onto N-terminal serine or threonine residues of peptides and proteins allowing them to be immobilised onto the sensor surface in a defined orientation. It is based on the specific reaction of the 1,2-aminothiol of cysteine with an aldehyde under acidic conditions to form a stable thiazolidine product. The carbonyl precursors are derived from the 1,2-aminoalcohols of Ser or Thr that can be selectively and rapidly converted to the aldehyde form by periodate oxidation. Biotinylation of the aldehyde is then achieved via simple conjugation with a novel water-soluble dipeptide that contains a lysine residue bearing an N-cysteine-derived 1,2-aminothiol and an N-biotin moiety. Use of this method allowed selective biotinylation of a native form of murine EGF (mEGF_2-53) that has an N-terminal serine residue. This derivative was then immobilised onto a streptavidin biosensor surface, and the resultant surface activity compared with those obtained by immobilising recombinant human EGF or the soluble extracellular domain of the EGF receptor (sEGFR_1-621) using amine coupling (NHS/EDC) chemistry.The surface recognised the recombinant sEGFR with a similar K_D to that of human EGF immobilised using NHS/EDC chemistry, or if the receptor was immobilised and murine EGF injected.     

Non-labeled detection of waterborne pathogen Cryptosporidium parvum using a polydiacetylene-based fluorescence chip

A non-labeling fluorescence sensor system was developed using polydiacetylene (PDA) liposomes composed of 10,12-pentacosadiynoic acid (PCDA) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at a 8:2 molar ratio. The PDA liposomes were immobilized onto an amine-coated glass surface using peptide bonding between the carboxyl group of the liposome and the amine group of the glass surface. The optimum ratio of the cross linker (NHS/EDC) to PDA liposome was determined to be 50% for strong immobilization of the liposomes. Residual carboxyl groups of the PDA liposomes were selectively biotinylated, followed by sequential binding of streptavidin and biotin-antibody (bioreceptor). Finally, the performance of the PDA liposome chip was tested for detecting Cryptosporidium parvum, and yielded a detection limit of 1 x 10(3) oocysts/mL. From these results, it is expected that the PDA liposome chip will have high application potential for the detection of waterborne pathogens including C. parvum.     

Capture of peptides with N-terminal serine and threonine: a sequence-specific chemical method for Peptide mixture simplification

The objective of this study was to evaluate a sequence-specific chemistry for the ability to specifically capture peptides that contain N-terminal serine or threonine residues from mixtures. The first step is the oxidation of the 1,2-amino alcohol structure -CH(NH(2))CH(OH)- of peptides containing N-terminal serine or threonine with periodate. The newly formed aldehyde reacts with a labeling reagent containing a hydrazide, RCONHNH(2), to form a hydrazone-peptide conjugate, RCONHN=CH-peptide. Biotin-labeled conjugates can then be isolated by affinity purification with streptavidin. The method described in this report can be useful in simplifying the complex mixtures of peptides that are generated in typical proteomic analysis, where proteins are digested with trypsin and analyzed using liquid chromatography mass spectrometry data. The sequence-specific peptide selection not only reduces the complexity of digest mixtures, but also provides additional information for peptide identification. The targeted peptides are those that have either serine or threonine adjacent to a protease cleavage site. The sequence information should greatly aid in both database matching for protein identification and for de novo sequence determination.     

Polyaniline-carbon nanotube composite film for cholesterol biosensor

Nanocomposite film composed of polyaniline (PANI) and multiwalled carbon nanotubes (MWCNT), prepared electrophoretically onto indium tin oxide (ITO)-coated glass plate, was used for covalent immobilization of cholesterol oxidase (ChOx) via N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) chemistry. Results of linear sweep voltammetric measurements reveal that ChOx/PANI-MWCNT/ITO bioelectrode can detect cholesterol in the range of 1.29 to 12.93 mM with high sensitivity of 6800 nA mM⁻¹ and a fast response time of 10 s. Photometric studies for ChOx/PANI-MWCNT/ITO bioelectrode indicate that it is thermally stable up to 45 °C and has a shelf life of approximately 12 weeks when stored at 4 °C. The results of these studies have implications for the application of this interesting matrix (PANI-MWCNT) toward the development of other biosensors.     

Predictive mutagenesis of ligation-independent cloning (LIC) vectors for protein expression and site-specific chemical conjugation

Ligation-independent cloning (LIC) allows for cloning of DNA constructs independent of insert restriction sites and ligases. However, any required mutations are typically introduced by additional, time-consuming steps. We present a rapid, inexpensive method for mutagenesis in the 5′ LIC site of expression constructs and report on the construction of expression vectors with N-terminal serine, cysteine, threonine, or tyrosine residues after tobacco etch virus (TEV) protease cleavage. In a practical application, the N-terminal serine was oxidized to an aldehyde, subsequently reacted with an amino-oxy functionalized polyethylene glycol (PEG) ligand under aniline catalysis to provide a protein selectively modified at the N-terminus.     

电化学方法在李斯特氏菌毒力基因检测中的应用

单核李斯特氏菌(Listeria monocytogenes, LM)是食源性李斯特氏病的病源菌, 该病可引起败血病、脑膜炎、流产等。李斯特氏菌的毒力因子listeriolysin O (LLO)是引发李斯特氏病的主要原因。文章使用一种特殊的电化学方法从样品中检测编码LLO的hlyA基因。该方法以化合物Nhydroxysulfosuccinimide (NHS) 和 N-(3-dimethylamion) propyl- N'-ethyl carbodiimidehydrochloride (EDC) 作为激活剂, 使单链DNA探针结合到金电极表面组成工作电极, 以[Co(phen)₃](ClO₄)₃ 作为指示剂来检测循环伏安曲线(Cyclic voltammetry , CV), 通过CV峰值的变化来估算hlyA基因的含量, 从而确定LM的污染情况。这种新颖的电化学方法用于免标记的目标DNA的杂交检测, 具有快速和方便的特点。     

Epidermal growth factor-PEG functionalized PAMAM-pentaethylenehexamine dendron for targeted gene delivery produced by click chemistry

Aim of this study was the site-specific conjugation of an epidermal growth factor (EGF)-polyethylene glycol (PEG) chain by click chemistry onto a poly(amido amine) (PAMAM) dendron, as a key step toward defined multifunctional carriers for targeted gene delivery. For this purpose, at first propargyl amine cored PAMAM dendrons with ester ends were synthesized. The chain terminal ester groups were then modified by oligoamines with different secondary amino densities. The oligoamine-modified PAMAM dendrons were well biocompatible, as demonstrated in cytotoxicity assays. Among the different oligoamine-modified dendrons, PAMAM-pentaethylenehexamine (PEHA) dendron polyplexes displayed the best gene transfer ability. Conjugation of PAMAM-PEHA dendron with PEG spacer was conducted via click reaction, which was performed before amidation with PEHA. The resultant PEG-PAMAM-PEHA copolymer was then coupled with EGF ligand. pDNA transfections in HuH-7 hepatocellular carcinoma cells showed a 10-fold higher efficiency with the polyplexes containing conjugated EGF as compared to the ligand-free ones, demonstrating the concept of ligand targeting. Overall gene transfer efficiencies, however, were moderate, suggesting that additional measures for overcoming subsequent intracellular bottlenecks in delivery have to be taken.     

Electric potential control of DNA immobilization on gold electrode

The assembly of synthetic, controllable molecules is one of the goals in nanotechnology. The primary objective of this contribution is to selectively immobilize DNA on gold via electric potential control. The self-assembly monolayer (SAM) was prepared with 2-aminoethanethiol (AET) on the gold electrode. A new approach based on electric potential was firstly used to control DNA immobilization covalently onto the SAM with the activation of 1-ethyl-3(3-dimethyl-aminopropyl)-carbodiimide (EDC) and N-hydroxysulfosuccinimide (NHS) in low ionic strength solution. The influence of electric potential on DNA immobilization was investigated by means of cyclic voltammogram, A.C. impedance, auger electron spectrometer as well as atomic force microscope (AFM) on template-stripped gold surface. The result proves that controlled potential can affect the course of DNA immobilization. More negative potential can restrain the DNA immobilization, while the more positive potential can accelerate the DNA immobilization. It is of great significance for the control of DNA self-assembly and will find wide application in the fields of DNA-based devices.     

The influence of inductive ligand electronics on the metrical parameters and redox potentials of a series of manganese(II) compounds

In order to assess the changes in the redox activity of a metal ion that result from inductive effects, three electronically modified derivatives of the ligand, N-benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (L^H), have been prepared: N-(4-nitro)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (L^NO2), N-(4-chloro)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (L^Cl), and N-(4-methoxy)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (L^OMe). Due to the lack of a fully conjugated π-system between the 4-benzyl substituent and the N-donors, the electronic perturbation should influence a bound metal ion’s redox properties through primarily inductive pathways. The organic ligands react with MnCl₂ to form mononuclear complexes with the general formula [Mn(L^R)Cl₂]. The parent ligand, L^H, and its three derivatives each coordinate Mn(II) ions in a cis-α conformation, with the amine N-donors installed trans to the Mn-Cl bonds. Despite its distance from the metal ion, the electron-donating or - withdrawing group has a notable impact on both the metrical parameters of the Mn(II) compounds and the Mn(III/II) reduction potential. A single inductive perturbation can vary the reduction potential by as much as 50 mV.     

An oriented adsorption strategy for efficient solid phase PEGylation of recombinant staphylokinase by immobilized metal-ion affinity chromatography

Conjugation of truncated recombinant staphylokinase (trSak) with polyethylene glycol (PEG) is an effective way to overcome its short plasma half-life and enhance its therapeutic potential. However, conventional amine directed PEGylation chemistry inevitably led to modification at its functionally important N terminus, which resulted in a significantly reduced bioactivity of trSak. In this study, a novel solid phase PEGylation process was developed to shield the N-terminal region of the protein from PEGylation. The process was achieved by oriented adsorption of an N-terminally His-tagged trSak (His-trSak) onto an immobilized metal-ion affinity chromatography (IMAC). His-trSak was efficiently separated and retained on IMAC media before reaction with succinimidyl carbonate mPEG (SC-mPEG, 5, 10 or 20 kDa). The IMAC derived mono-PEGylated His-trSak showed structural and stability properties similar to the liquid phase derived conjugate. However, isoelectric focusing electrophoresis analysis revealed that mono-PEGylated His-trSaks via solid phase PEGylation were more homogeneous than those from liquid phase PEGylation. Moreover, tryptic peptide mapping analysis suggested that a complete N-terminal blockage of IMAC bound His-trSak from PEGylation with 10 kDa- and 20 kDa-SC-mPEG. In contrast, only partial protection of the N-terminal region was obtained for 5 kDa-SC-mPEG. Bioactivities of 10 kDa- and 20 kDa-PEG-His-trSak conjugates without N-terminal PEGylation were significantly higher than those of randomly PEGylated products. This further demonstrated the advantage of our new on-column PEGylation strategy.     

Preparation and use of synthetic cell culture surfaces. A new reagent for the covalent immobilization of proteins and glycoproteins on a nonionic inert matrix

To study cell interactions with external molecules immobilized on a chemically defined nonionic, inert matrix, we have prepared flat polyacrylamide matrices containing covalently attached carbohydrate or protein. A new acrylamide derivative, containing a terminal 1,2-dihydroxy group, was synthesized and then copolymerized with acrylamide and bisacrylamide to make 20% polyacrylamide matrices, which could be oxidized with NaIO4 to generate reactive aldehyde groups. Molecules containing a free amine (e.g. proteins or glycopeptides) can be coupled to the aldehyde-activated matrix by formation of a Schiff base and reduction with NaCNBH3 to form a stable -CH2-NH-bond. Unreacted aldehyde groups are reduced to hydroxyl groups with NaBH4. In order to immobilize polysaccharides on the activated surfaces, these molecules are first modified to contain a free amine. We have described a procedure to convert purified hyaluronic acid oligosaccharides to a reactive alkylamine derivative uniquely modified at the reducing end (Raja, R. H., LeBoeuf, R. D., Stone, G. W., and Weigel, P. H. (1984) Anal. Biochem. 139, 168-177). The covalent attachment of [3H]hyaluronate-amine, [14C]ethanolamine, or 125I-bovine serum albumin, to activated surfaces was complete within 5-24 h. The amount immobilized was directly proportional to the amine concentration and to the aldehyde content of the matrix and inversely proportional to the molecular weight of the amine. About 90% of the available aldehyde groups reacted with ethanolamine, whereas less than 0.01% reacted with albumin. Molecules larger than 3300 Da were excluded from the interior of the matrix and could therefore only be attached to the surface of the matrix. These synthetic surfaces can be used in long term culture experiments to study cellular interactions with virtually any type of immobilized molecule.     

Immobilisation of oligo-peptidic probes for microarray implementation: characterisation by FTIR, atomic force microscopy and 2D fluorescence

Proteomic microarrays show a wide range of applications for the investigation of DNA-protein, enzyme-substrate as well as protein-protein interactions. Among many challenges to build a viable "protein microarray", the surface chemistry that will allow to immobilised various proteins to retain their biological activity is of paramount importance. Here we report a chemical functionalisation method allowing immobilisation of oligo-peptides onto silica surface (porous silica, glass, thermal silicon dioxide). Substrates were first derivatised with a monofunctional silane allowing the elaboration of dense and uniform monolayers in highly reproducible way. Prior to the oligo-peptides grafting, this organic layer was functionalised with an amino-polyethyleneglycol. The coupling step of oligo-peptides onto functionalised supports is achieved through activation of the C-terminal function of the oligo-peptides. Chemical surface modifications were followed by FTIR spectroscopy, AFM measurements and fluorescence scanning microscopy. A systematic study of the oligo-peptide grafting conditions (time, concentration, solvent) was carried out to optimise this step. The oligo-peptides grafting strategy implemented in this work ensure a covalent and oriented grafting of the oligo-peptides. This orientation is ensured through the use of fully protected peptide except the terminal primary amine. The immobilized peptides will be then deprotected before biological recognition. This strategy is crucial to retain the biological activity of thousands of oligo-probes assessed on a microarray.     

Electron beam-induced graft polymerization of acrylic acid and immobilization of arginine-glycine-aspartic acid-containing peptide onto nanopatterned polycaprolactone

Electron beam- (EB-) induced graft polymerization of acrylic acid and the subsequent immobilization of arginine-glycine-aspartic acid (RGD) peptide onto nanopatterned polycaprolactone with parallel grooves is reported. A high concentration of carboxylic groups was introduced onto the polymer substrate by EB-induced polymerization of acrylic acid. In the coupling of the RGD peptide to the carboxylated polymer surface, a three-step peptide immobilization process was used. This process included the activation of surface carboxylic acid into an active ester intermediate by use of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), the introduction of disulfide groups by use of 2-(2-pyridinyldithio)ethanamine hydrochloride (PDEA), and final immobilization of the peptide via a thiol-disulfide exchange reaction. The extent of coupling was measured by UV spectroscopy. A preliminary study of the in vitro behavior of keratinocytes (NCTC 2544) cultured on the acrylic acid-grafted and RGD peptide-coupled surface showed that most cells grown on the coupled samples had a spread-rounded appearance, while the majority of cells tended to be elongated along the grooves on uncoupled substrates.     

Polyaniline protected gold nanoparticles based mediator and label free electrochemical cortisol biosensor

Polyaniline protected gold nanoparticles (PPAuNPs) were electrophoretically deposited onto a gold electrode, and utilized to fabricate an electrochemical cortisol biosensor. Cortisol specific monoclonal antibody (C-Mab) was covalently immobilized onto the surface of a PPAuNP/Au electrode using N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) chemistry. BSA was employed for blocking nonspecific adsorption on the electrode surface. PPAuNP formation and BSA/C-Mab/PPAuNP/Au electrode fabrication were characterized using transmission electron microscopy, atomic force microscopy and electrochemical impedance techniques, respectively. Cyclic voltammetry and differential pulse voltammetric techniques were used to determine the cortisol concentration in a phosphate buffer saline (PBS) solution. Results confirmed that the PPAuNP based electrode was stable during repeated scans and exhibited repeatable redox peaks. Further, the BSA/C-Mab/PPAuNP/Au electrode in the PBS buffer accurately detected cortisol in the range of 1 pM-100 nM with a sensitivity of 1.63 μAM(-1). The biosensor was found to be selective against BSA and 17-α-hydroxy progesterone. This research establishes the feasibility of using a PPAuNP based matrix for a label and mediator free electrochemical biosensor for cortisol, a stress biomarker.     

Nano-Au/cMWCNT Modified <Emphasis Type="Italic">speB</Emphasis> Gene Specific Amperometric Sensor for Rapidly Detecting <Emphasis Type="Italic">Streptococcus pyogenes</Emphasis> causing Rheumatic Heart Disease

A specific 5′ NH₂ labeled DNA probe of speB gene was immobilized onto the gold nanoparticles/carboxylated multi walled carbon nanotubes (Nano-Au/cMWCNT) screen printed electrode using EDC/NHS cross linking chemistry. This was followed by hybridization with 0.5–50 ng/6 µl of single stranded genomic DNA Streptococcus pyogenes infected patient throat swab samples. Electrochemical amperometric assay was deciphered by using cyclic voltammetry (CV) with methylene blue a redox indicator. The sensor had a sensitivity of 104.7 µA cm^?2 ng^?1 using CV with a R² of 0.907 and 0.01 ng/6 µl as the limit of detection (LOD). The modified electrode surface morphology was characterized using scanning electron microscopy. The stability of the electrode was seen at 4 °C for 180 days having 6% loss in the initial current. The sensor is speB gene specific and can detect the pathogen within 30 min.     

cAMP-mediated modulation of signal transduction of epidermal growth factor (EGF) receptor systems in human epidermoid carcinoma A431 cells. Depression of EGF-dependent diacylglycerol production and EGF receptor phosphorylation.

While a cAMP-dependent protein kinase (protein kinase A) has been suggested to phosphorylate epidermal growth factor (EGF) receptor in vitro, both intrinsic and EGF- or potent phorbol tumor promoter-induced phosphorylation of EGF receptor were found to be depressed in human epidermoid carcinoma A431 cells by prior incubation of the cells with various protein kinase A activators (e.g. cholera toxin, forskolin, cAMP analogues, or a combination of prostaglandin E1 and 3-isobutyl-1-methylxanthine). Protein kinase A activators did not change significantly either the number of EGF receptors or their affinity for EGF. The tryptic phosphopeptide map of EGF receptors from cells treated with cholera toxin alone or cholera toxin followed by EGF revealed unique peptides whose serine phosphorylation was preferentially depressed. However, the catalytic subunit of protein kinase A phosphorylated no threonine and little serine in the EGF receptors in the plasma membranes of isolated A431 cells in vitro, while serine residues in an unidentified 170-kDa membrane protein(s) other than EGF receptor were heavily phosphorylated. Pretreatment of the cells with forskolin blocked 1,2-diacylglycerol induction by EGF; growth inhibition by nanomolar levels of EGF could be partially restored by the presence of forskolin. These results indicate that an increase in intracellular cAMP modulates the EGF receptor signal transduction system by reducing EGF-induced production of diacylglycerol without direct phosphorylation of EGF receptors by protein kinase A in A431 cells.     

Surface modification of nanofibrous poly(acrylonitrile-co-acrylic acid) membrane with biomacromolecules for lipase immobilization

In this work, poly(acrylonitrile-co-acrylic acid) (PANCAA) was electrospun into nanofibers with a mean diameter of 180 nm. To create a biofriendly microenvironment for enzyme immobilization, collagen or protein hydrolysate from egg skin (ES) was respectively tethered on the prepared nanofibrous membranes in the presence of 1-ethyl-3-(dimethyl-aminopropyl) carbodiamine (EDC)/N-hydroxyl succinimide (NHS). Confocal laser scanning microscopy (CLSM) was used to verify the surface modification and protein density on the nanofibrous membranes. Lipase from Candida rugosa was then immobilized on the protein-modified nanofibrous membranes by covalent binding using glutaraldehyde (GA) as coupling agent, and on the nascent PANCAA nanofibrous membrane using EDC/NHS as coupling agent, respectively. The properties of the immobilized enzyme were assayed. It was found that different pre-tethered biomacromolecules had distinct effects on the immobilized enzyme. The activity retention of the immobilized lipase on ES hydrolysate-modified nanofibrous membrane increased from 15.0% to 20.4% compared with that on the nascent one, while it was enhanced up to more than quadrupled (activity retention of 61.7%) on the collagen-modified nanofibrous membrane. The kinetic parameter, K_m and V_max, were also determined for the free and immobilized lipases. Furthermore, the stabilities of the immobilized lipases were obviously improved compared with the free one.     

Bonding of articular cartilage using a combination of biochemical degradation and surface cross-linking

After trauma, articular cartilage often does not heal due to incomplete bonding of the fractured surfaces. In this study we investigated the ability of chemical cross-linkers to facilitate bonding of articular cartilage, either alone or in combination with a pre-treatment with surface-degrading agents. Articular cartilage blocks were harvested from the femoropatellar groove of bovine calves. Two cartilage blocks, either after pre-treatment or without, were assembled in a custom-designed chamber in partial apposition and subjected to cross-linking treatment. Subsequently, bonding of cartilage was measured as adhesive strength, that is, the maximum force at rupture of bonded cartilage blocks divided by the overlap area. In a first approach, bonding was investigated after treatment with cross-linking reagents only, employing glutaraldehyde, 1-ethyl-3-diaminopropyl-carbodiimide (EDC)/N-hydroxysuccinimide (NHS), genipin, or transglutaminase. Experiments were conducted with or without compression of the opposing surfaces. Compression during cross-linking strongly enhanced bonding, especially when applying EDC/NHS and glutaraldehyde. Therefore, all further experiments were performed under compressive conditions. Combinations of each of the four cross-linking agents with the degrading pre-treatments, pepsin, trypsin, and guanidine, led to distinct improvements in bonding compared to the use of cross-linkers alone. The highest values of adhesive strength were achieved employing combinations of pepsin or guanidine with EDC/NHS, and guanidine with glutaraldehyde. The release of extracellular matrix components, that is, glycosaminoglycans and total collagen, from cartilage blocks after pre-treatment was measured, but could not be directly correlated to the determined adhesive strength. Cytotoxicity was determined for all substances employed, that is, surface degrading agents and cross-linkers, using the resazurin assay. Taking the favourable cell vitality after treatment with pepsin and EDC/NHS and the cytotoxic effects of guanidine and glutaraldehyde into account, the combination of pepsin and EDC/NHS appeared to be the most advantageous treatment in this study. In conclusion, bonding of articular cartilage blocks was achieved by chemical fixation of their surface components using cross-linking reagents. Application of compressive forces and prior modulation of surface structures enhanced cartilage bonding significantly. Enzymatic treatment in combination with cross-linkers may represent a promising addition to current techniques for articular cartilage repair.     

Oligonucleotides containing 2'-O-[2-(2,3-dihydroxypropyl)amino-2-oxoethyl]uridine as suitable precursors of 2'-aldehyde oligonucleotides for chemoselective ligation

2'-O-[2-(2,3-Diacetoxypropyl)amino-2-oxoethyl]uridine 3'-phosphoramidite was prepared and used in solid-phase synthesis to obtain oligonucleotides containing a 1,2-diol group, which may then be converted into a 2'-aldehyde group. The oligonucleotides were conjugated efficiently to various molecules by chemoselective ligation that involves an addition-elimination reaction between the 2'-aldehyde group and a suitable nucleophile, such as a hydrazine, a O-alkylhydroxylamine or an 1,2-aminothiol. The method was applied successfully to the conjugation of peptides to oligonucleotides at the 2'-position.