TAILIEUCHUNG - Báo cáo khoa học: Key role of the loop connecting the two beta strands of mussel defensin in its antimicrobial activity

To elucidate the structural features of the mussel defensin MGD1 required for antimicrobial activity, we synthesized a series of peptides corresponding to the main known secon-dary structures of the molecule and evaluated their activity towards Gram-positive and Gram-negative bacteria, and filamentous fungi. We found that the nonapeptide corres-ponding to residues 25–33 of MGD1 (CGGWHRLRC) exhibited bacteriostatic activity once it was cyclized by a non-naturally occurring disulfide bridge. | Eur. J. Biochem. 270 2805-2813 2003 FEBS 2003 doi Key role of the loop connecting the two beta strands of mussel defensin in its antimicrobial activity Bernard Romestand1 Franck Molina2 Veronique Richard1 Philippe Roch1 and Claude Granier2 1DRIM Université Montpellier 2 France 2Centre de Biotechnologie et Pharmacologie pour la Sante CNRS UMR Montpellier France To elucidate the structural features of the mussel defensin MGD1 required for antimicrobial activity we synthesized a series of peptides corresponding to the main known secondary structures of the molecule and evaluated their activity towards Gram-positive and Gram-negative bacteria and filamentous fungi. We found that the nonapeptide corresponding to residues 25-33 of MGD1 cGGwHRLRC exhibited bacteriostatic activity once it was cyclized by a non-naturally occurring disulfide bridge. Longer peptides corresponding to the amino acid sequences of the a-helical part or to the b-strands of MGD1 had no detectable activity. The bacteriostatic activity of the sequence 25-33 was strictly dependent on the bridging of Cys25 and Cys33 and was proportional to the theoretical isoelectric point of the peptide as deduced from the variation of activity in a set of peptide analogues of the 25-33 sequence with different numbers of cationic charges. By using confocal fluorescence microscopy we found that the cyclic peptides bound to Gram-positive bacteria without apparent lysis. However by using a fluorescent dye we observed that dead bacteria had been permeated by the cyclic peptide 25-33. Sequence comparisons in the family of arthopod defensins indicate that MGD1 belongs to a subfamily of the insect defensins characterized by the constant occurrence of both positively charged and hydrophobic amino acids in the loop. Modelling studies showed that in the MGD1 structure positively charged and hydrophobic residues are organized in two layered clusters which might have a functional significance in .

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