Peptide loops

A very good example is the study of the extent to which residues of the loop polypeptide of lysozyme contributes to specificity. The loop peptide comprises residues 64-80 in which Cys-64 and Cys-80 form a disulfide bond, and thus this structure is highly conformational because opening the disulfide bond destroyed immunological activity. From the X-ray crystallographic study (Fig. 13), the loop peptide occurs in an exposed position. Figure 14 shows the sequence of the synthetic loop peptide and the capacity of synthetic loop peptides containing residues modified... 

Fig. 14. Effects of replacement by Ala of the indicated residues in the synthetic loop peptide of lysozyme on ability to inhibit inactivation by antiloop antibodies of bacteriophage-loop conjugate. From Amon et and Teicher et al. ...

The antigenic determinants proposed by Atassi do not include the loop peptide 64-82 (Fig. 13) to which Maron et al. found 8-10 mg of antibody per 100 mg of goat antilysozyme -these antibodies were more restricted in heterogeneity than the total antilysozyme. 

Takahashi, M. Nokihara, K. Mihara, H., Construction of a protein-detection system using a loop peptide library with a fluorescence label. Chem. Biol. 2003, 10, 53-60... 

Fonseca MI, Aguilar JS, Skorupa AF, Klein WL. 1991a. Cellular mapping of m2 muscarinic receptors in the rat olfactory bulb using antiserum raised against a cytoplasmic loop peptide. Brain Res 563 163-170. 

Au/PANI-CSA coaxial nanocables have been successfully synthesized by the oxidation of aniline with chloroauric acid in the presence of CSA [397]. PANI-CSA nanotubes were obtained by dissolving the Au nanowire core of the Au/PANI-CSA nanocables. Purified flagella fibers displaying an anionic aspartate-glutamate loop peptide with 18 carboxylate groups were used to initiate formation of PANI-NTs [398]. 

Figure 3. Glycoforms of an extracellular loop peptide from nAChR...

The V3 loop peptides (approximately 40 residues based on the V3 structure of X4 and R5X4 viruses) have been shown to exert anti-HIV activity against X4 viruses (Sakaida et al, 1998). These peptides do not induce calcium mobilization upon binding the CXCR4 receptor they function as true antagonists. 

Sakaida, H., Hori, T., Yonezawa, A., Sato, A., Isaka, Y., Yoshie, O., Hattori, T., and Uchiyama, T. (1998). T-tropic human immunodeficiency virus type 1 (HlV-l)-derived V3 loop peptides directly bind to CXCR-4 and inhibit T-tropic HIV-1 infection. J. Virol. 72, 9763-9770. 

Only the peptide identical with the central loop B bound to the acetylcholine receptor, whereas the other peptides had no detectable binding. The disulfide bond is essential for binding. When the central loop peptide was reduced and alkylated, the binding ability was lost. This finding suggested that the central loop plays a dominant role in the toxin s ability to bind the receptor. 

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