Structure-Function Characterization and Optimization of a Plant-Derived Antibacterial Peptide

Abstract

Crushed seeds of the Moringa oleifera tree have been used traditionally as natural flocculants to clarify drinking water. We previously showed that one of the seed peptides mediates both the sedimentation of suspended particles such as bacterial cells and a direct bactericidal activity, raising the possibility that the two activities might be related. In this study, the conformational modeling of the peptide was coupled to a functional analysis of synthetic derivatives. This indicated that partly overlapping structural determinants mediate the sedimentation and antibacterial activities. Sedimentation requires a positively charged, glutaminerich portion of the peptide that aggregates bacterial cells. The bactericidal activity was localized to a sequence prone to form a helix-loop-helix structural motif. Amino acid substitution showed that the bactericidal activity requires hydrophobic proline residues within the protruding loop. Vital dye staining indicated that treatment with peptides containing this motif results in bacterial membrane damage. Assembly of multiple copies of this structural motif into a branched peptide enhanced antibacterial activity, since low concentrations effectively kill bacteria such as Pseudomonas aeruginosa and Streptococcus pyogenes without displaying a toxic effect on human red blood cells. This study thus identifies a synthetic peptide with potent antibacterial activity against specific human pathogens. It also suggests partly distinct molecular mechanisms for each activity. Sedimentation may result from coupled flocculation and coagulation effects, while the bactericidal activity would require bacterial membrane destabilization by a hydrophobic loop.Diverse communities in the world traditionally use different natural agents from animal or vegetal sources as raw water additives to produce drinking water. Systematic studies have shown that among the different plant-derived materials tested, Moringa oleifera seeds seem to be one of the most effective primary water treatments (17, 28). Water-soluble proteins released from the crushed seed kernels function as natural flocculating agents, which have been proposed to bind and crosslink particles suspended in a colloidal structure, forming larger sedimenting particles (17,18,29). Microorganisms are generally attached to solid particles in raw water samples, and treatment employing Moringa seed powder can remove over 90% of the bacterial load (35). Unexpectedly, a study on the sedimentation effect of the seed-derived peptide termed Flo indicated also that it mediates bacterial disinfection, being able to kill antibiotic-resistant bacteria, including several human pathogens (62).The cationic nature of the Flo polypeptide is characteristic of a wider group of cationic peptide antibiotics that are usually less than 10 kDa in size and display an overall net positive charge. Cationic antimicrobial peptides (AMPs) make part of the innate immunity response, which is the first line of defense against pathogens. Most of the AMPs are expressed constitu...

Bioactivity of phytochemicals in some lesser-known plants and their effects and potential applications in livestock and aquaculture production systems

“…The bacterial resistance to antibiotics is increasing in various regions and this obviously has huge implications in curing infectious diseases and in using antibiotics in feeds as growth promoters. The moringa protein also has bactericidal activity (Suarez et al, 2005). Gram-positive and Gram-negative bacteria, pathogenic to humans, showed only a slight reduction of viability with the moringa protein (Suarez et al, 2005), while viability of E. coli was inhibited by four orders of magnitude (Suarez et al, 2003).…”

“…The moringa protein also has bactericidal activity (Suarez et al, 2005). Gram-positive and Gram-negative bacteria, pathogenic to humans, showed only a slight reduction of viability with the moringa protein (Suarez et al, 2005), while viability of E. coli was inhibited by four orders of magnitude (Suarez et al, 2003). The use of antibacterial moringa proteins for controlling mastitis is also being investigated by us.…”

Coagulant proteins identified in Mustard: a potential water treatment agent

“…In earlier reports, Moringa coagulant protein identified as a 6.5 kDa protein possesses three alpha helices structure by computer simulation modelling studies and has coagulation activity (Ghebremichael et al 2005;Broin et al 2002;Suarez et al 2005;Okoli 2012). Since two interesting protein bands of 9 and 6.5 kDa (Fig.…”

“…5c), indicating its plausible association to possess synergetic coagulation activity in mustard. Suarez et al (2005) reported a computer simulated hypothetical model of coagulant protein of MO2.1 using napin3 as a homolog. The fact that the seed storage protein is acting as a coagulating agent is quite useful, as the abundant protein in commonly used Mustard would provide a cheaper source for commercial exploitation.…”

Antibacterial effect (in vitro) of Moringa oleifera and Annona muricata against Gram positive and Gram negative bacteria

“…The moringa plant (Moringa oleifera) has been the object of much research due to its multiple uses and well-known bactericidal potential 9,37,17,38 . According to BEZERRA et al 8 , the moringa tree is native to northeastern India.…”