Circular dichroism study of the unfolding-refolding of a cardiotoxin from Taiwan cobra (Naja naja atra) venom

Fusogenicity of Naja naja atra cardiotoxin-like basic protein on sphingomyelin vesicles containing oxidized phosphatidylcholine and cholesterol

This study investigated the effect of oxidized phosphatidylcholine (oxPC) and cholesterol (Chol) on Naja naja atra cardiotoxin-like basic protein (CLBP)-induced fusion and leakage in sphingomyelin (SM) vesicles. Compared with those on PC/SM/Chol vesicles, CLBP showed a lower activity to induce membrane permeability but a higher fusogenicity on oxPC/SM/Chol vesicles. A reduction in inner-leaflet fusion elucidated that CLBP fusogenicity was not in parallel to its membrane-leakage activity on oxPC/SM/Chol vesicles. The lipid domain formed by Chol and SM supported CLBP fusogenicity on oxPC/SM/Chol vesicles, while oxPC altered the interacted mode of CLBP with oxPC/SM/Chol vesicles as evidenced by Fourier transform infrared spectra analyses and colorimetric phospholipid/polydiacetylene membrane assay. Although CLBP showed similar binding affinity with PC/SM/Chol and oxPC/SM/Chol vesicles, the binding capability of CLBP with PC/SM/Chol and oxPC/SM/Chol vesicles was affected differently by NaCl. This emphasized that CLBP adopted different membrane interaction modes upon binding with PC/SM/Chol and oxPC/SM/Chol vesicles. CLBP induced fusion in vesicles containing oxPC bearing the aldehyde group, and aldehyde scavenger methoxyamine abrogated the CLBP ability to induce oxPC/SM/Chol fusion. Taken together, our data indicate that Chol and oxPC bearing aldehyde group alter the CLBP membrane-binding mode, leading to fusogenicity promotion while reducing the membrane-damaging activity of CLBP.

Monitoring protein refolding induced by disulfide formation using capillary isoelectric focusing-electrospray ionization mass spectrometry

Rapid growth in the biotechnology industry has led to a dramatic increase in attention to the protein folding problem. Understanding protein-folding pathways is essential to the production of biopharmaceuticals since commercial production of recombinant proteins often requires a protein-refolding process for recovery of high yields. Protein folding coupled to the formation of disulfide bonds presents one of the simplest approaches to studying folding intermediates. On-line capillary isoelectric focusing-electrospray ionization mass spectrometry (CIEF-ESIMS) is demonstrated for kinetic studies of disulfide bond-induced protein refolding. Refolding intermediates of bovine pancreatic ribonuclease A, a model system for this study, are blocked at different stages by alkylating free thiols with iodoacetate. The alkylation reaction results in the introduction of charge (-1) and mass (59) differences for each alkylation site, providing the means for predictable separation and direct identification of refolding intermediates using CIEF-ESIMS. Besides the observation of refolding intermediates containing different numbers of disulfide bonds and even mixed disulfides, the two-dimensional resolving power of CIEF-ESIMS allows the determination of conformational heterogeneity among groups of refolding intermediates.

Interaction of riboflavin binding protein with riboflavin, quinacrine, chlorpromazine and daunomycin

1. circular dichroism and fluorescence measurements were used to study the reversible unfolding of riboflavin-riboflavin binding protein complex. Both methods showed that the complex was unfolded according to the two-state model. 2. The results suggest that riboflavin was strongly bound in the hydrophobic cleft of the protein and that it could not be dislodged by TFE, MeOH or SDS without major unfolding of the unique tertiary structure of the protein. 3. In addition, it has been also shown that quinacrine, chlorpromazine and daunomycin did not form stereospecific complexes with riboflavin binding protein.

Detection of intermediate species in the refolding of bovine trypsinogen

The mixed disulfide of bovine trypsinogen and glutathione was refolded at pH 8.6 and 4 degrees C with a mixture of 3 mM cysteine and 1 mM cystine catalyzing disulfide interchange. The folding process was monitored by analysis of quenched samples with isoelectric focusing and size-exclusion chromatography. Isoelectric focusing showed a progressive change from a pI of 5.2 for the mixed disulfide derivative to a pI of 9.3 for native trypsinogen. A number of principal intermediates were detected as a function of the refolding time. These intermediates were also separated and further characterized by size-exclusion chromatography on columns of TSK G2000 SW operated in the high-performance liquid chromatographic mode. Rechromatography of a series of sequential fractions taken from the parental peak was necessary to resolve and characterize the principal intermediates. The loss of glutathione moieties produced a partly folded structure with an apparent hydrodynamic volume (Stokes radius, Rs) of 33.9 A. These structures became compact with time, and more intermediates were detected between 33.9 and 29.2 A. Finally, a change in conformation, resembling a two-state transition, changed the molecules of Rs 29.2 to the compact structure of native trypsinogen (22.4 A). The rate of formation of the native structure was determined from the progress curves derived from isoelectric focusing and size-exclusion chromatography.(ABSTRACT TRUNCATED AT 250 WORDS)