Cyanogen bromide and tresyl chloride chemistry revisited: the special reactivity of agarose as a chromatographic and biomaterial support for immobilizing novel chemical groups

Modulation of the Biocatalytic Properties of a Novel Lipase from Psychrophilic Serratia sp. (USBA-GBX-513) by Different Immobilization Strategies

In this work, the effect of different immobilization procedures on the properties of a lipase obtained from the extremophilic microorganism Serratia sp. USBA-GBX-513, which was isolated from Paramo soils of Los Nevados National Natural Park (Colombia), is reported. Different Shepharose beads were used: octyl-(OC), octyl-glyoxyl-(OC-GLX), cyanogen bromide (BrCN)-, and Q-Sepharose. The performance of the different immobilized extremophile lipase from Serratia (ESL) was compared with that of the lipase B from Candida antarctica (CALB). In all immobilization tests, hyperactivation of ESL was observed. The highest hyperactivation (10.3) was obtained by immobilization on the OC support. Subsequently, the thermal stability at pH 5, 7, and 9 and the stability in the presence of 50% (v/v) acetonitrile, 50% dioxane, and 50% tetrahydrofuran solvents at pH 7 and 40 °C were evaluated. ESL immobilized on octyl-Sepharose was the most stable biocatalyst at 90 °C and pH 9, while the most stable preparation at pH 5 was ESL immobilized on OC-GLX-Sepharose supports. Finally, in the presence of 50% (v/v) tetrahydrofuran (THF) or dioxane at 40 °C, ESL immobilized on OC-Sepharose was the most stable biocatalyst, while the immobilized preparation of ESL on Q-Sepharose was the most stable one in 40% (v/v) acetonitrile.

Methodologies to anchor dendrimeric nanoconjugates to solid phase: toward an efficient in vitro detection of allergy to β-lactam antibiotics

β-lactam antibiotics are the most common cause of adverse drug reactions, and in vitro immunoassays are often employed to diagnose this allergy. Cellulose solid supports displaying hapten-carrier conjugates are traditionally used for quantifying specific IgE antibodies to determine whether a patient is allergic to the hapten. Our approach makes use of polyamidoamine dendrimers as carriers, and differs from traditional solid-phase activation methods by using two different haloalkanoyl halides as reagents instead of cyanogen bromide. Evaluation of the functionalization in the three different surfaces with benzylpenicilloyl-dendrimer conjugates showed a higher density of conjugates when using haloalkanoyl halides. The resulting surfaces were evaluated in vitro by radioimmunoassay using sera from patients allergic to penicillins. Selective and specific IgE recognition was observed in the different activated disks, though those activated with haloalkanoyl halides presented better sensitivity.

FROM THE CLINICAL EDITOR

A novel and sensitive method of dendrimeric nanoconjugate-based in vitro detection of allergy to β-lactam antibiotics is presented in this basic science paper.

Screening biomaterials for functional complement activation in serum

Complement plays an important role in the immune attack against invading microorganisms. However, blood-contacting medical device biomaterials lacking specific complement inhibitors, with free hydroxyl and/or amino groups, or with absorbed antibodies, may inappropriately activate complement. Inappropriate activation by either the antibody-mediated classical or the antibody-independent alternative pathway may have well-known acute or poorly understood chronic effects on the host or device. This article describes methods for screening biomaterials for functional whole complement activation using normal human serum, or specifically for alternative pathway activation using C4-deficient guinea pig serum, or for classical pathway activation using both sera in combination. Detailed protocols are available as standard methodologies from the American Society for Testing and Materials (ASTM F1984, ASTM F2065, and ASTM F2567). Results obtained with these functional tests are confirmed by detection of classical and alternative pathway-specific markers C4d and Bb, respectively. These methods demonstrate dose and time-course activation of complement to beaded agarose, cellulose acetate, and purified alginate as examples of biomaterials. Significant difference in a functional endpoint denoting specific complement pathways is an appropriate screening method for complement activation by medical device biomaterials which might result in adverse events when the device is implanted or contacts human blood.

Interaction of fibrinogen with n-alkylagaroses and its purification by critical hydrophobicity hydrophobic interaction chromatograpy

A rational application of hydrophobic interaction chromatography (HIC) to the purification of proteins has remained an enigma in spite of over 30 years of research. The critical hydrophobicity parameter, which can be determined from a concentration series of n-alkyl Sepharose 4B (Seph-Cn) offers the possibility of adapting the HIC gel to the needs of purification. To this end a library of HIC gels (Seph-C4 to Seph-C6) of different immobilized alkyl residue concentrations was synthesized and tested with purified bovine fibrinogen. Binding of fibrinogen to such a concentration series resulted in sigmoidal binding curves. Analysis of the Seph-C5 data according to the lattices-site binding model yielded adsorption coefficients (nS) between 5 and 10 indicating that 5-10 lattice-sites (alkyl residues) interact multivalently with a fibrinogen molecule for adsorption at low ionic strength. The apparent lattice-site half-saturation constant of dissociation lies between 21 and 25 micromol/ml packed gel. For each alkyl chain length a critical hydrophobicity could be determined. For fibrinogen purification the critical hydrohobicity gel, Seph-C5 (13 micromol/ml packed gel), was selected. With the help of the cosolvents NaCl or glycine a fully reversible adsorption of fibrinogen could be facilitated on the critical hydrophobicity gel. Application of the method to human and bovine blood plasma resulted in a single step purification of fibrinogen in high yields. A comparison of the classical purification of fibrinogen with the critical hydrophobicity HIC (CHIC) method demonstrates a reduction in preparation time from several days to ca. 1 h. The subunit structure of HIC-purified human fibrinogen is identical to the classically purified protein. In the case of bovine fibrinogen however HIC-purified fibrinogen displayed a different subunit structure in that the Aalpha chain of fibrinogen had a ca. 5 kDa higher molecular mass. This may be due to the rapidity of the new one-step method and an avoidance of proteolysis.

A proteomic survey of rat cerebral cortical synaptosomes

Previous findings from our laboratory and others indicate that two-dimensional gel electrophoresis (2-DE) can be used to study protein expression in defined brain regions, but mainly the proteins which are present in high abundance in glia are readily detected. The current study was undertaken to determine the protein profile in a synaptosomal subcellular fraction isolated from the cerebral cortex of the rat. Both 2-DE and liquid chromatography - tandem mass spectrometry (LC-MS/MS) procedures were used to isolate and identify proteins in the synaptosomal fraction and accordingly >900 proteins were detected using 2-DE; the 167 most intense gel spots were isolated and identified with matrix-assisted laser desorption/ionization - time of flight peptide mass fingerprinting or LC-MS/MS. In addition, over 200 proteins were separated and identified with the LC-MS/MS "shotgun proteomics" technique, some in post-translationally modified form. The following classes of proteins associated with synaptic function were detected: (a) proteins involved in synaptic vesicle trafficking-docking (e.g., SNAP-25, synapsin I and II, synaptotagmin I, II, and V, VAMP-2, syntaxin 1A and 1B, etc.); (b) proteins that function as transporters or receptors (e.g., excitatory amino acid transporters 1 and 2, GABA transporter 1); (c) proteins that are associated with the synaptic plasma membrane (e.g., post-synaptic density-95/synapse-associated protein-90 complex, neuromodulin (GAP-43), voltage-dependent anion-selective channel protein (VDACs), sodium-potassium ATPase subunits, alpha 2 spectrin, septin 7, etc.); and (d) proteins that mediate intracellular signaling cascades that modulate synaptic function (e.g., calmodulin, calcium-calmodulin-dependent protein kinase subunits, etc.). Other identified proteins are associated with mitochondrial or general cytosolic function. Of the two proteins identified as endoplasmic reticular, both interact with the synaptic SNARE complex to regulate vesicle trafficking. Taken together, these results suggest that the integrity of the synaptosomes was maintained during the isolation procedure and that this subcellular fractionation technique enables the enrichment of proteins associated with synaptic function. The results also suggest that this experimental approach can be used to study the differential expression of multiple proteins involved in alterations of synaptic function.

Analysis of affinity supports by 13C CP/MAS NMR spectroscopy: application to carbonyldiimidazole- and novel tresyl chloride-synthesized agarose and silica gels

A major problem in affinity technology is the analysis of the synthesized solid supports, since liquid phase methodology can generally not be applied. Recently we reported a novel reaction sequence for the 2,2,2-trifluoroethanesulfonyl chloride (tresyl chloride) coupling of nucleophiles [Demiroglou et al. (1994) Angew. Chem. Int. Ed. Engl. 33, 120-123] to agarose and concluded that previously proposed structures could not be correct. However it was not possible for us to conclusively define the new reaction products because the agarose derivatives could not be solubilized for customary liquid state 13C NMR analysis. Therefore in this paper solid state 13C CP/MAS NMR spectroscopy is applied for the first time to the polysacharide agarose. Using alkyl agarose derivatives prepared by the carbonyldiimidazol method as control we found that reliable spectra in agreement with the published reaction mechanism could be obtained. The method was then applied to the novel reaction products of the tresyl chloride reaction. From the solid state 13C NMR spectra and other quantitative data it is concluded that a beta-sulfonyl carboxylic acid is generated during alkaline hydrolysis of tresyl agarose and that alkyl amines are coupled by a beta-sulfonyl amide bond in an elimination-addition reaction in the absence of SO- and SC-scission of the tresyl group. In the case of alkane thiol coupling the absence of SC-scission cannot be demonstrated indicating either a different reaction mechanism or possibly a mixture of reaction products.