Some theoretical considerations regarding the effects of steric hindrance and intrinsic global coupling on the flexibility of Fc-anchored immunoglobulins

Nanosecond fluorescence depolarization studies reported in the accompanying companion paper showed that the long rotational correlation time, phi L, increased somewhat when rabbit IgG anti-dansyl antibodies were anchored in staphylococcal protein A (SpA) soluble complexes. The increases in phi L upon anchoring IgG probably resulted from "global coupling" effects caused by: increased steric hindrance of the antibody segments in the SpA complexes and intrinsic structural constraints already present in the monomeric IgG. Global coupling results from a restriction in the angular range of a flexible segment and is manifest when flexible motions alone cannot depolarize all of the fluorescence, so that the slower global tumbling of the entire particle is also required. Such effects cannot be resolved directly from experimental anisotropy data, however, because only a single long correlation time, phi L, is well defined over the limited time range of most fluorophores. In this paper, estimates of the anisotropy contributions from flexible and global motions of the IgG-SpA complexes are determined by contrasting theoretical and measured decays. For this analysis it was assumed that each of the experimental phi L-values is a weighted composite of the rotational correlation time associated with the less restricted flexible motions of the Fab arms, phi F, and the correlation time associated with global tumbling of the entire particle, phi G. A general two-exponential expression was used to relate phi F and phi G to phi L. This approach was meaningful because phi G-values of the various SpA complexes had been calculated from hydrodynamic measurements. The theoretical decays clearly show that, even if phi G is much longer than phi F, these two rotational motions still cannot be resolved over the experimentally accessible time range. Families of emission anisotropy decay curves for IgG antibodies with different amounts of intrinsic global coupling and for anchored antibodies with different amounts of steric hindrance were simulated by varying the preexponential weighting factors of the flexible and global terms. By comparing the calculated curves with the measured decays, it is evident that the rabbit IgG anti-dansyl antibodies do not have much intrinsic global coupling, but rather they are highly flexible. The curves also indicate that even for the exceptionally compact IgG4-SpA2 17-S complex, which showed the most steric hindrance in electron micrographs, the appropriate phi G weighting factor is only 0.28. Thus, as supposed earlier, the anchored antibodies exhibit considerable segmental flexibility. In closing, the above concepts are used to examine the results of     

QUANTITATION OF SOME AMINO-TERMINAL RESIDUES IN PROTEINS USING 3H-LABELLED DANSYL CHLORIDE AND 14C-LABELLED AMINO ACIDS

A method for quantitation of amino-terminal residues in proteins is presented. The method is a modification of a double isotope-labelling technique, using ³H-labelled dansyl chloride and ¹⁴C-labelled amino acids as internal standards. The method is demonstrated on human fibrinogen, horse myoglobin and on mouse myoloma IgA. A linear relationship between the ratio ³H/¹⁴C in the separated amino-terminal amino acid of the protein and the amount of protein added in the labelling mixture was obtained with standard deviations of ±7.4%, ±3.4% and ±10.3%, respectively. An application of the method is demonstrated by measuring the increase in amino-terminal glycine in fibrinogen following the proteolytic action of thrombin. The method seems to be useful when 0.1 nmol or more of protein is used.     

Monoliths with chiral surface functionalization for enantioselective capillary electrochromatography

The state-of-the-art in CEC enantiomer separations with monolithic capillary columns is comprehensively reviewed. The various types of monolithic columns comprising in situ organic polymer monoliths, molecularly imprinted polymer (MIP) monoliths, silica monoliths and monoliths made from particles are discussed with a focus on materials’ synthesis, chemistry and properties as well as column aspects. Monolithic MIP-type porous layer open-tubular (PLOT) columns are treated herein as well. From this survey of the literature, the authors come to the conclusion that monolithic silica capillaries appear to become the preferred column type for CEC enantiomer separations of low-molecular drugs and other chiral pharmaceuticals or chemicals.     

Rotational dynamics of immunoglobulin G antibodies anchored in protein A soluble complexes

The rotational dynamics of rabbit IgG anti-dansyl antibodies anchored in staphylococcal protein A (SpA) soluble complexes were studied by both steady-state and nanosecond fluorescence spectroscopy. To aid in the interpretation of the anisotropy data, the results of recently reported hydrodynamic and electron microscopic studies of IgG-SpA complexes were used to calculate global tumbling times of the various complexes and to estimate the steric hindrance of the antibody Fab segments. The anisotropy decays, fitted to the sum of two exponentials, indicated that the Fab arms of antibodies bound to SpA by their Fc regions exhibit considerable flexibility. For the different IgG-SpA mixtures examined, changes in the IgG preexponential anisotropy weighting factors, fS and fL, and the short rotational correlation time, phi S, were relatively small. On the other hand, the long rotational correlation time, phi L, increased systematically when the percentage of larger IgG-SpA complexes in a mixture was increased. The greatest restriction of Fab flexibility was observed for antibodies anchored in the exceptionally compact IgG4-SpA2 complexes. Available electron microscopic data suggest that increases in phi L correlate with increased steric hindrance of the antibody segments. Both native and hinge-disulfide-cleaved IgG experienced similar percentage increases in phi L when bound in SpA complexes. In agreement with our earlier interpretation, the results of this study provide rather striking evidence that phi L mainly represents flexible motions of the Fab segments and not global tumbling: the phi L-values of IgG bound in the various SpA complexes ranged from 101 to 162 nsec, whereas the calculated global tumbling times of the different complexes ranged from about 300 to 3000 nsec.     

海马神经元中TAT-GluR6-9c-dansyl小肽的荧光观察

目的 研究TAT-GluR6-9c-dansyl荧光小肽是否可以进入细胞内部.方法 在培养的海马神经元中加入TAT-GluR6-9c-dansyl荧光小肽和对照肽TAT38-48-dansyl.结果用10 μmol/L TAT-GluR6-9c-dansyl处理的海马神经元在荧光显微镜下可以观到绿色荧光的出现,而对照肽TAT38-48-dansyl无荧光出现.结论 TAT-GluR6-9c-dansyl荧光小肽可以进入细胞.     

葡萄酒中生物胺多组分的UVD/FLD串联HPLC方法研究

目的建立葡萄酒中多组分生物胺的柱前衍生反相高效液相色谱-荧光/紫外串联检测器的测定方法。方法以正丁醇/氯仿(1∶1)为萃取液提取葡萄酒中生物胺,丹磺酰氯为衍生剂,1,7-二氨基庚烷为定量内标,采用C18色谱柱分离,甲醇/水为流动相梯度洗脱,流速1.5ml/min,紫外检测波长254nm,荧光激发波长(Ex)350nm,发射波长(Em)520nm。结果色胺、苯乙胺、腐胺、尸胺、组胺、酪胺、精胺和亚精胺在30分钟内得到良好分离。在给定的浓度范围内,各组分生物胺呈现良好线性相关(r>0.99)。在葡萄酒中添加生物胺混合标准溶液,平均回收率为79.2%~127.9%,相对标准偏差RSD小于10%。结论采用荧光/紫外检测器串联方法检测,满足了葡萄酒中多组分生物胺检测的需要。     

Synthesis and biological evaluation of biotinyl hydrazone derivatives of muramyl peptides

Muramyl peptides derived from bacterial peptidoglycan have long been known for their ability to trigger host innate immune responses, including inflammation and antimicrobial defense. Muramyl peptides have also been widely studied for their role as immune adjuvants. In mammals, the nucleotide-binding oligomerization domain (Nod) proteins Nod1 and Nod2 detect distinct muramyl peptide structures and mediate their biological activity. Because of the poor immunogenicity of these small peptidoglycan derivatives, research in this field is currently limited by the lack of reagents to track or immobilize specific muramyl peptides. We present here the generation and initial biological characterization of synthetic muramyl peptides covalently coupled to dansyl or biotinyl derivatives and demonstrate that biotinyl coupling on the muramyl moiety results in derivatives that can be tracked by immunofluorescence and maintain full biological activity, as observed by their capacity to trigger Nod signaling. Moreover, using digitonin-mediated permeabilization techniques on live cells, we also demonstrate that biotinylated muramyl peptides efficiently reach the host cytosol, where they activate Nod signaling. Therefore, these derivatives represent useful probes to study the cell biology and the biochemistry of host responses to muramyl peptides.     

Immunologically active nonapeptide fragment of a proline-rich polypeptide from ovine colostrum: Amino acid sequence and immunoregulatory properties

It has been previously found that a proline-rich polypeptide (PRP) isolated from ovine colostrum has a regulatory effect on the immune response. To study the relationship between the structure of PRP and its immunomodulatory properties, the polypeptide was digested by chymotrypsin. Products of the proteolysis were separated by gel filtration and three fractions were obtained: PRP-1, PRP-2 and PRP-3. The activity of the fractions was compared with the activity of the untreated PRP. It was found that PRP-1 was inactive, whereas PRP-2 and PRP-3 showed an activity in the regulation of the immune response assayed by measurement of PFC, and by studying effects on delayed hypersensitivity, formation of autologous rosette-forming cell, and sensitivity of thymocytes to hydrocortisone. The activity of PRP-2 and PRP-3 was comparable to the activity of PRP. The PRP-3 fraction of low mol. wt was further purified and a pure nonapeptide of mol. wt 1000 (PRP-3b) was isolated. The amino acid sequence of PRP-3b was: Val—Glu—Ser—Tyr—Val—Pro—Leu—Phe—Pro. The nonapeptide showed the full spectrum of biological activities of PRP. Comparison of terminal amino acid suggested that PRP-3b was neither the NH₂- nor the COOH-terminal fragment of PRP. The amino acid sequence of the nonapeptide indicated that PRP-3b is different from other known immunomodulators.     

Neurophysin-neurohypophyseal hormone interactions: studies using dansylated vasotocin analogue

We have synthesized a neurohypophyseal hormone analogue containing an extrinsic fluorescence probe by linking a dansyl (DNS) group to the ε-amino group of the lysine at residue 8 of vasotocin. The fluorescence properties of this analogue have been characterized by steady-state and time-resolved spectroscopic methods and compared with those of ε-DNS-lysine and the dansylated carboxyl terminal tripeptide Pro-Lys(DNS)-GlyNH₂. The binding of this hormone analogue to purified isoforms of bovine neurophysins, the natural carrier proteins of the neurohypophyseal hormones, results in changes in several fluorescence parameters of the dansyl probe. These changes include an increase in intensity and average lifetime, a shift of the emission band to higher energies, and an increase in the emission anisotropy. Anisotropy changes have been used to determine dissociation constants for binding to these neurophysin isoforms. Based on the changes in the fluorescence properties of the dansyl probe, the dansyl group itself interacts with the protein. The degree of the dansyl-neurophysin interaction, however, appears to be different for the full sequence isoform of neurophysin I and the Val⁸⁹ isoform of neurophysin II.