RESUMO
The peptide antibiotic clavanin A (VFQFLGKIIHHVGNFVHGFSHVF-NH(2)) is rich in histidine and glycine residues. In this study the antimicrobial activity and membrane activity of wild-type clavanin A and seven Gly --> Ala mutants thereof were investigated. Clavanin A effectively killed the test microorganism Micrococcus flavus and permeabilized its cytoplasmic membrane in the micromolar concentration range, suggesting that the membrane is the target for this molecule. Consistent with this suggestion, it was observed that clavanin A efficiently inserted into different phospholipid monolayers mainly via hydrophobic interactions. Bilayer permeabilization was observed for both low and high molecular mass fluorophores enclosed in unilamellar vesicles and occurred at the same concentration as the antimicrobial activity. It is therefore suggested that the loss of barrier function does not involve specific receptors in the target membrane. Circular dichroism spectroscopy indicated that under membrane mimicking conditions a random coil --> helical transition was induced for all clavanin derivatives tested. Observed differences in peptide-membrane interaction and biological activity between the various clavanin derivatives demonstrated the functional importance of Gly at the positions 6 and 13. These two glycines may act as flexible hinges that facilitate the hydrophobic N-terminal end of clavanin to deeply insert into the bilayer. On the contrary, no such role is evident for Gly 18, as its substitution by Ala actually stimulated membrane interaction and biological activity. This study suggests that the combined hydrophobicity, overall state of charge, and conformational flexibility of the peptide determine the (membrane) activity of clavanin A and its Gly --> Ala mutants.
Assuntos
Antibacterianos/metabolismo , Proteínas Sanguíneas/metabolismo , Glicina/fisiologia , Lipossomos/metabolismo , Peptídeos , Fosfatidiletanolaminas , Alanina/genética , Sequência de Aminoácidos , Substituição de Aminoácidos/genética , Animais , Antibacterianos/síntese química , Antibacterianos/farmacologia , Proteínas Sanguíneas/síntese química , Proteínas Sanguíneas/genética , Proteínas Sanguíneas/farmacologia , Membrana Celular/efeitos dos fármacos , Membrana Celular/fisiologia , Dicroísmo Circular , Glicerofosfolipídeos/metabolismo , Glicina/genética , Bicamadas Lipídicas/metabolismo , Potenciais da Membrana/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Micrococcus/efeitos dos fármacos , Micrococcus/crescimento & desenvolvimento , Micrococcus/fisiologia , Dados de Sequência Molecular , Permeabilidade/efeitos dos fármacos , Fosfatidilgliceróis/metabolismoRESUMO
The authors report toxicity caused by valacyclovir in a patient on hemodialysis. After initial recuperation resulting from treatment with hemodialysis, the patient experienced a relapse of neurologic symptoms, again necessitating hemodialysis. Although acyclovir and its analogues are generally safe drugs, they should be used with caution in patients with end-stage renal disease. Therapeutic drug monitoring may be indicated.
