Rationale based , de novo design of dehydrophenylalanine containing 1 antibiotic peptides and systematic modification in sequence for 2 enhanced potency 3 “

13 Running title-de novo design of novel antimicrobial peptides 14 Abstract 21 Increased microbial drug resistance has generated a global requirement for new anti 22 infective agents. As part of an effort to develop new, low molecular mass peptide 23 antibiotics we used a rationale based minimalist approach to design short, non hemolytic, 24 potent and broad spectrum antibiotic peptides with increased serum stability. These 25 peptides were designed to attain an amphipathic structure in helical conformations. VS1 26 was used as the lead compound and its properties were compared with three series of 27 derivates obtained by 1) N-terminal amino acid addition, 2) systematic Trp substitution 28 and 3) peptide dendrimerization. The Trp substitution approach underlined the optimized 29 sequence of VS2 in terms of potency, faster membrane permeation and cost effectiveness. 30 VS2 (two Trp substituted variant of VS1) was found to exhibit good antimicrobial 31 activity against both, Gram negative E. coli and Gram positive bacteria S. aureus. It was 32 also found to have non cytolytic activity and ability to permeate and depolarize the 33 bacterial membrane. Lysis of bacterial cell wall and inner membrane by the peptide was 34 confirmed by Transmission Electron Microscopy. A combination of small size, presence 35 of unnatural amino acid, high antimicrobial activity, insignificant hemolysis and 36 proteolytic resistance provides fundamental information towards the de novo design of an 37 antimicrobial peptide useful for the management of infectious disease.