Synthesis and antibody recognition of mucin 1 (MUC1)-alpha-conotoxin chimera

Drugs from slugs. Part II--conopeptide bioengineering

The biological transformation of toxins as research probes, or as pharmaceutical drug leads, is an onerous and drawn out process. Issues regarding changes to pharmacological specificity, desired potency, and bioavailability are compounded naturally by their inherent toxicity. These often scuttle their progress as they move up the narrowing drug development pipeline. Yet one class of peptide toxins, from the genus Conus, has in many ways spearheaded the expansion of new peptide bioengineering techniques to aid peptide toxin pharmaceutical development. What has now emerged is the sequential bioengineering of new research probes and drug leads that owe their lineage to these highly potent and isoform specific peptides. Here we discuss the progressive bioengineering steps that many conopeptides have transitioned through, and specifically illustrate some of the biochemical approaches that have been established to maximize their biological research potential and pharmaceutical worth.

Antibody recognition and conformational flexibility of a plaque-specific beta-amyloid epitope modulated by non-native peptide flanking regions

Here we report on the synthesis, antibody binding, and QSAR studies of a series of linear and cyclic peptides containing a beta-amyloid plaque-specific epitope (Abeta(4-10); FRHDSGY). In these constructs, two or three alpha- l-Ala, alpha- d-Ala, or beta-Ala residues were introduced at both N- and C-termini of the epitope as non-native flanking sequences. Cyclization of the linear Abeta(4-10) epitope peptide resulted in reduced antibody binding. However, the antibody binding could be fully compensated by insertion of alanine flanks into the corresponding cyclic peptides. These results indicate that the modification of a beta-amyloid plaque-specific epitope by combination of cyclization and flanking sequences could generate highly antigenic peptides compared to the native sequence. A novel 3D QSAR method, which explicitly handles conformational flexibility, was developed for the case of such molecular libraries. This method led to the prediction of the binding conformation for the common FRHDSGY sequence.

Antibodies to citrullinated human fibrinogen synthetic peptides in diagnosing rheumatoid arthritis

Since aggressive therapy given early in the rheumatoid arthritis (RA) disease course has the greatest therapeutic potential, early diagnostic tests with both high specificity and sensitivity are desirable. Rheumatoid sera were found to contain antibodies against citrullinated peptides, which are considered to be highly specific markers of RA. In the present work several analogues of the alpha- and beta-chains of fibrin peptides containing different degrees of citrullination have been synthesized and analyzed by ELISA using 111 sera from RA patients. In addition, we have also investigated the synergistic effects of different presentation formats of the synthetic constructs. We have designed chimeric and cyclic peptides that bear different peptide sequences within the same molecule. Our results indicate that the synthesis of peptides bearing fibrinogen and filaggrin domains could be a robust method for the design of useful diagnostic strategies in RA.

Engineered proteins as specific binding reagents

Over the past 30 years, monoclonal antibodies have become the standard binding proteins and currently find applications in research, diagnostics and therapy. Yet, monoclonal antibodies now face strong competition from synthetic antibody libraries in combination with powerful library selection technologies. More recently, an increased understanding of other natural binding proteins together with advances in protein engineering, selection and evolution technologies has also triggered the exploration of numerous other protein architectures for the generation of designed binding molecules. Valuable protein-binding scaffolds have been obtained and represent promising alternatives to antibodies for biotechnological and, potentially, clinical applications.

Disulfide bond rearrangement during regioselective oxidation in PhS(O)Ph/CH3SiCl3 mixture for the synthesis of alpha-conotoxin GI

Rearrangement of disulfide bonds during the synthesis of alpha-conotoxin GI using PhS(O)Ph/CH(3)SiCl(3) oxidation procedure was observed. We have demonstrated that the protecting scheme (order of acetamidomethyl (Acm) and (t)Bu protecting groups) of the Cys residues as well as the reaction time influenced the ratio of the native and the mispaired compounds, while the temperature of the reaction mixture had no significant effect. However, in all cases the nonnative derivative was produced in high amount. The structure of the isomers was identified by the combination of enzymatic digestion and mass spectrometry measurements. We conclude that the air oxidation followed by the application of Tl(tfa)(3) for the regioselective formation of disulfide bonds leads up to the appropriate compound in the case of the synthesis of alpha-conotoxin GI, while the oxidation procedure using PhS(O)Ph/CH(3)SiCl(3) system resulted in the nonnative disulfide isomer.

[Natural alpha-conotoxins and their synthetic analogues in studies of nicotinic acetylcholine receptors]

alpha-Conotoxins, peptide neurotoxins from poisonous marine snails of the genus Conus that highly specifically block nicotinic acetylcholine receptors (AChRs) of various types, are reviewed. Preliminarily, the structural organization of AChRs of the muscular and neuronal types, their involvement in physiological processes, and their role in various diseases are briefly discussed. In this connection, the necessity of quantitative determination of AChR subtypes using neurotoxins and other approaches is substantiated. The chemical structure, spatial organization, and specificity of alpha-conotoxins are mainly discussed, taking into consideration the recent results on the ability of alpha-conotoxins to interact with muscular or neuronal hetero- and homooligomeric AChRs exhibiting a high species specificity. Particular emphasis is placed upon a thorough characterization of the surfaces of interaction of alpha-conotoxins with AChRs using synthetic analogues of alpha-conotoxins, mutations in AChRs, and pairwise mutations in both alpha-conotoxins and AChRs. The discovery in 2001 of the acetylcholine-binding protein from the pond snail Lymnaea stagnalis and the determination of its crystalline structure led to rapid progress in understanding the structural organization of ligand-binding domains of AChRs with which alpha-conotoxins also interact. We discuss the interaction of various alpha-conotoxins with acetylcholine-binding proteins, the recently reported X-ray structure of the complex of the acetylcholine-binding protein from Aplysia californica with the alpha-conotoxin analogue PnIA, and the application of this structure to the modeling of complexes of alpha-conotoxins with various AChRs.

Antigenicity of chimeric and cyclic synthetic peptides based on nonstructural proteins of GBV-C/HGV

In this work, new putative epitopes located in nonstructural proteins of GBV-C/HGV were synthesized using solid-phase chemistry for their use in immunoassays. The antigens were obtained in linear, chimeric and cyclic forms with the main aim of improving the sensitivity of the enzyme immunoassays. Our results showed, on one hand, that the combination of different antigens seems to be necessary to ensure good sensitivity and more specificity and, on the other hand, that cyclic compounds show higher ability to recognize anti-GBV-C/HGV antibodies than its parent peptide. Furthermore, CD and FTIR have been used in conjunction to characterize the conformational changes therein with synthetic constructs that could explain their different antigenicity.

Manipulation of epitope function by modification of peptide structure: a minireview

We have explored various approaches to modify the immunrecognition of linear peptides representing sequential or continuous topographic B-cell or T-cell epitopes. For these studies, epitopes from herpes simplex virus (HSV) glycoprotein D (gD) and from mucin 1 and mucin 2 glycoproteins or T-cell epitopes from 16 kDa and 38 kDa proteins of Mycobacterium tuberculosis were selected. To increase antigenicity and immunogenicity we have prepared cyclic and chimaeric peptide variants as well as epitope peptides with altered flanking regions and epitope-carrier conjugates containing multiple epitope copies.

lambda-conotoxins, a new family of conotoxins with unique disulfide pattern and protein folding. Isolation and characterization from the venom of Conus marmoreus

Conotoxins are multiple disulfide-bonded peptides isolated from marine cone snail venom. These toxins have been classified into several families based on their disulfide pattern and biological properties. Here, we report a new family of Conus peptides, which have a novel cysteine motif. Three peptides of this family (CMrVIA, CMrVIB, and CMrX) have been purified from Conus marmoreus venom, and their structures have been determined. Their amino acid sequences are VCCGYK-LCHOC (CMrVIA), NGVCCGYKLCHOC (CMrVIB), and GICCGVSFCYOC (CMrX), where O represents 4-trans-hydroxyproline. Two of these peptides (CMrVIA and CMrX) have been chemically synthesized. Using a selective protection and deprotection strategy during disulfide bond formation, peptides with both feasible cysteine-pairing combinations were generated. The disulfide pattern (C(1)-C(4), C(2)-C(3)) in native toxins was identified by their co-elution with the synthetic disulfide-isomeric peptides on reverse-phase high pressure liquid chromatography. Although cysteine residues were found in comparable positions with those of alpha-conotoxins, these toxins exhibited a distinctly different disulfide bonding pattern; we have named this new family "lambda -conotoxins." CMrVIA and CMrX induced different biological effects when injected intra-cerebroventricularly in mice; CMrVIA induces seizures, whereas CMrX induces flaccid paralysis. The synthetic peptide with lambda-conotoxin folding is about 1150-fold more potent in inducing seizures than the mispaired isomer with alpha-conotoxin folding. Thus it appears that the unique disulfide pattern, and hence the "ribbon" conformation, in lambda-conotoxins is important for their biological activity.