Location of disulfide bonds in mature alpha-L-fucosidase from pea

A novel interaction mode between acrylamide and its specific antibody

Since the discovery of high-level acrylamide (Acr) contamination in food, extensive international studies have focused on its toxicity and detection. By using a novel antigen synthetic strategy, we have successfully obtained a specific antibody towards acrylamide (Acr-Ab). Herein, the Acr-Ab and its interactions with Acr were characterized. Enzyme-linked immunosorbent assay (ELISA) and dynamic light scattering (DLS) investigations revealed that the conformational structure of Acr-Ab was sensitive to buffers. It showed a satisfied immunoreactivity in phosphate buffered saline (PBS), but denatured in water. In natural state, Acr-Ab had a trend of getting aggregation through their complementarity determining regions (CDRs). Adding Acr leaded to their disassembling. While mixed with Acr, Acr-Ab exhibits not only a fast, high-specific, and reversible non covalent binding (by surface plasmon resonance, SPR), but also a covalent alkylation with Acr through cysteine and histidine residues on its surface, as demonstrated by high-performance liquid chromatography (HPLC). Neither of the two reactions involves conformational change in secondary or tertiary structures as shown in circular dichroism spectra (CD). These special properties of Acr-Ab and the entirely new interaction mode with Acr will extend our knowledge of Acr related biosystem and facilitate the development of new detection strategies for Acr.

Probing protein structure by amino acid-specific covalent labeling and mass spectrometry

For many years, amino acid-specific covalent labeling has been a valuable tool to study protein structure and protein interactions, especially for systems that are difficult to study by other means. These covalent labeling methods typically map protein structure and interactions by measuring the differential reactivity of amino acid side chains. The reactivity of amino acids in proteins generally depends on the accessibility of the side chain to the reagent, the inherent reactivity of the label and the reactivity of the amino acid side chain. Peptide mass mapping with ESI- or MALDI-MS and peptide sequencing with tandem MS are typically employed to identify modification sites to provide site-specific structural information. In this review, we describe the reagents that are most commonly used in these residue-specific modification reactions, details about the proper use of these covalent labeling reagents, and information about the specific biochemical problems that have been addressed with covalent labeling strategies.

Differential labeling of free and disulfide-bound thiol functions in proteins

A method for the simultaneous determination of the number of free cysteine groups and disulfide-bound cysteine groups in proteins has been developed based on the sequential labeling of free and bound thiol functionalities with two ferrocene-based maleimide reagents. Liquid chromatography/electrochemistry/mass spectrometry was used to assign the N-(2-ferroceneethyl)maleimide (FEM) labeled free cysteine functionalities in a tryptic digest mixture, whereas a precursor ion scan enables the detection of peptides with ferrocenecarboxylic acid-(2-maleimidoyl)ethylamide (FMEA) labeled disulfide-bound cysteine groups after reduction. Fragment spectra of the labeled peptides yield an excellent coverage of b-type and y-type ions. The ferrocene labeled cysteines were fragmented as 412 Da (FEM) and 455 Da (FMEA). These fragment masses are significantly higher than unlabeled amino acids or dipeptides and are easily detected. The position of free and disulfide-bound cysteine may therefore be assigned in an amino acid sequence.

GH mutant (R77C) in a pedigree presenting with the delay of growth and pubertal development: structural analysis of the mutant and evaluation of the biological activity

A heterozygous missense mutation in the GH-1 gene converting codon 77 from arginine (R) to cysteine (C), which was previously reported to have some GH antagonistic effect, was identified in a Syrian family. The index patient, a boy, was referred for assessment of his short stature (-2.5 SDS) at the age of 6 years. His mother and grandfather were also carrying the same mutation, but did not differ in adult height from the other unaffected family members. Hormonal examination in all affected subjects revealed increased basal GH, low IGF-I concentrations, and subnormal IGF-I response in generation test leading to the diagnosis of partial GH insensitivity. However, GH receptor gene (GHR) sequencing demonstrated no abnormalities. As other family members carrying the GH-R77C form showed similar alterations at the hormonal level, but presented with normal final height, no GH therapy was given to the boy, but he was followed through his pubertal development which was delayed. At the age of 20 years he reached his final height, which was normal within his parental target height. Functional characterization of the GH-R77C, assessed through activation of Jak2/Stat5 pathway, revealed no differences in the bioactivity between wild-type-GH (wt-GH) and GH-R77C. Detailed structural analysis indicated that the structure of GH-R77C, in terms of disulfide bond formation, is almost identical to that of the wt-GH despite the introduced mutation (Cys77). Previous studies from our group demonstrated a reduced capability of GH-R77C to induce GHR/GH-binding protein (GHBP) gene transcription rate when compared with wt-GH. Therefore, reduced GHR/GHBP expression might well be the possible cause for the partial GH insensitivity found in our patients. In addition, this group of patients deserve further attention because they could represent a distinct clinical entity underlining that an altered GH peptide may also have a direct impact on GHR/GHBP gene expression causing partial GH insensitivity. This might be responsible for the delay of growth and pubertal development. Finally, we clearly demonstrate that GH-R77C is not invariably associated with short stature, but that great care needs to be taken in ascribing growth failure to various heterozygous mutations affecting the GH-IGF axis and that careful functional studies are mandatory.

Characterization and structural role of disulfide bonds in a highly knotted thionin from Pyrularia pubera

Disulfide bonds play a crucial role in the stabilization of the amphipathic folding of the diverse families of cysteine-rich antimicrobial peptides. The determination of cysteine pairings in these peptides has largely depended on sequence homology criteria, since the classical methods of disulfide bond characterization, which usually require proteolysis as a first step, encounter serious drawbacks derived from the tight folding and the presence of vicinal cysteines. We have chosen the Pyrularia pubera thionin, a 47-residue peptide with four internal disulfides and a remarkable resistance to most proteases, as a representative member of this type of cysteine-rich peptides and have shown that a combination of partial reduction and cyanylation readily allows the determination of its disulfide bonds. We have also studied by molecular dynamics and a combination of partial reduction and proteolysis the role of disulfide bonds in the stabilization of the tridimensional structure of this thionin and found a good agreement with our partial reduction data, suggesting that removal of only one disulfide bond is enough to significantly alter the folding of the peptide.

An alpha-L-fucosidase from Thermus sp. with unusually broad specificity

An alpha-L-fucosidase (E.C. 3.2.1.51) exhibiting a wide aglycon specificity expressed in ability of cleaving alpha1 --> 6-, alpha1 -->3-, alpha1 --> 4-, and alpha1 --> 2-O-fucosyl bonds in fucosylated oligosaccharides, has been isolated from culture filtrate of Thermus sp. strain Y5. The alpha-L-fucosidase hydrolyzes p-nitrophenyl alpha-L-fucopyranoside with V(max) of 12.0 +/- 0.1 microM/min/mg and K(m) = 0.20 +/- 0.05 mM and is able to cleave off about 90% of total L-fucose from pronase-treated fractions of fucosyl-containing glycoproteins and about 30% from the native glycoproteins. The purified enzyme is a tetramer with a molecular mass of 240 +/- 10 kDa consisting of four identical subunits with a molecular mass of 61.0 +/- 0.5 kDa. The N-terminal sequence showed homology to some alpha-L-fucosidases from microbial and plant sources. Hydrolysis of p-nitrophenyl alpha-L-fucopyranoside occurs with retention of the anomeric configuration. Transglycosylating activity of the alpha-L-fucosidase was demonstrated in reactions with such acceptors as alcohols, N-acetylglucosamine and N-acetylgalactosamine while no transglycosylation products were observed in the reaction with p-nitrophenyl alpha-L-fucopyranoside. The enzyme can be classified in glycosyl hydrolase family 29.