The stereochemical effect of SMAP-29 and SMAP-18 on bacterial selectivity, membrane interaction and anti-inflammatory activity
Binu Jacob, Ganesan Rajasekaran, Eun Young Kim, Il-Seon Park, Jeong-Kyu Bang, Song Yub Shin
Sheep myeloid antimicrobial peptide-29 (SMAP-29) is a cathelicidin-related antimicrobial peptide derived from sheep myeloid cells. In order to investigate the effects of l-to-d-amino acid substitution in SMAP-29 on bacterial selectivity, membrane interaction and anti-inflammatory activity, we synthesized its two d-enantiomeric peptides (SMAP-29-E1 and SMAP-29-E2 containing d-Ile and d-allo-Ile, respectively) and two diastereomeric peptides (SMAP-29-D1 and SMAP-29-D2). Additionally, in order to address the effect of l-to-d-amino acid substitution in the N-terminal helical peptide of SMAP-29 (named SMAP-18) on antimicrobial activity, we synthesized its two d-enantiomeric peptides (SMAP-18-E1 and SMAP-18-E2), which are composed of d-amino acids entirely. l-to-d-amino acid substitution in membrane-targeting AMP, SMAP-29 did not affect its antimicrobial activity. However, d-allo-Ile containing-SMAP-29-E2 and SMAP-29-D2 exhibited less hemolytic activity compared to d-Ile containing-SMAP-29-E1 and SMAP-29-D1, respectively. l-to-d-amino acid substitution in intracellular targeting-AMPs, SMAP-18 and buforin-2 improved antimicrobial activity by 2- to eightfold. The improved antimicrobial activity of the d-isomers of SMAP-18 and buforin-2 seems to be due to the stability against proteases inside bacterial cells. Membrane depolarization and dye leakage suggested that the membrane-disruptive mode of SMAP-29-D1 and SMAP-29-D2 is different from that of SMAP-29, SMAP-29-E1, and SMAP-29-E2. l-to-d-amino acid substitution in SMAP-29 improved anti-inflammatory activity in LPS-stimulated RAW 264.7 cells. In summary, we propose here that d-allo-Ile substitution is a more powerful strategy for increasing bacterial selectivity than d-Ile substitution in the design of d-enantiomeric and diastereomeric AMPs. SMAP-29-D1, and SMAP-29-D2 with improved bacterial selectivity and anti-inflammatory activity can serve as promising candidates for the development of anti-inflammatory and antimicrobial agents.
Circular dichroism, Stereochemistry, Biochemistry