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The outer membrane of Gram-negative bacteria is composed of an asymmetric bilayer of lipopolysaccharide(LPS)and phospholipids.The presence of LPS in the outer membrane in Gram-negative pathogens provides a formidable barrier for other antibiotics.We have a designed branched peptide(B2088,(RGRKVVRR)2kK,where k is a branched lysine core)that displayed excellent antibacterial activities against various Gram-negative pathogens(MIC = 1.4 – 5.5 μM).The peptide disrupts the supramolecular organization of LPS and targets the cytoplasmic membrane.NMR studies showed that the two valine residues in each copy play an important role in the binding of the peptide to LPS.To understand the role of two valine residues,we replaced the later by glycine residues(B2088_99,(RGRKVGGRR)2kK)and investigated their antimicrobial and LPS binding properties.