Isolation of peptides of the brevinin‐1 family with potent candidacidal activity from the skin secretions of the frog Rana boylii

Abstract: The emergence of strains of the human pathogen Candida albicans with resistance to commonly used antibiotics has necessitated a search for new types of antifungal agents. Six peptides with antimicrobial activity were isolated from norepinephrine‐stimulated skin secretions from the foothill yellow‐legged frog Rana boylii. Brevinin‐1BYa (FLPILASLAA¹⁰KFGPKLF CLV²⁰TKKC) was particularly potent against C. albicans [minimal inhibitory concentration (MIC) = 3 μm ] and also active against Escherichia coli (MIC = 17 μm ) and Staphylococcus aureus (MIC = 2 μm ), but its therapeutic potential for systemic use is limited by its strong hemolytic activity (HC₅₀ = 4 μm ). The single amino acid substitution (Phe¹² → Leu) in brevinin‐1BYb resulted in a fourfold lower potency against C. albicans and the additional amino acid substitutions (Lys¹¹ → Thr, Phe¹⁷ → Leu and Val²⁰ → Ile) in brevinin‐1BYc resulted in a ninefold decrease in activity. Two members of the ranatuerin‐2 family and one member of the temporin family were also isolated from the secretions but showed relatively low potency against the three microorganisms tested.     

Cytolytic peptides belonging to the brevinin-1 and brevinin-2 families isolated from the skin of the Japanese brown frog, Rana dybowskii.

Peptidomic analysis of an extract of the skins of specimens of Dybowski's brown frog Rana dybowskii Gunther, 1876, collected on Tsushima Island, Japan led to the identification of 10 peptides with differential antibacterial and hemolytic activities. The primary structures of these peptides identified them as belonging to the brevinin-1 (5 peptides) and brevinin-2 (5 peptides) families of antimicrobial peptides. A peptide (FIGPIISALASLFG.NH(2)) with structural similarity to members of the temporin family was also isolated but this component lacked cytolytic activity. Phylogenetic relationships among the Japanese brown frogs (R. dybowskii, R. japonica, R. okinavana, R. ornativentris, R. pirica, R. sakuraii, R. tagoi, and R. tsushimensis) are only incompletely understood. Cladograms based upon maximum parsimony analyses of the brevinin-1 and brevinin-2 amino acid sequences provide strong support for a sister-group relationship between R. dybowskii and R. pirica and somewhat weaker support for a sister-group relationship between R. okinavana and R. tsushimensis. These conclusions are consistent with previous analyses based upon allozyme variations and comparisons of the nucleotide sequences of mitochondrial genes.     

Identification and characterization of novel host defense peptides from the skin secretion of the fungoid frog,Hydrophylax bahuvistara (Anura: Ranidae)

Two novel peptides (brevinin1 HYba1 and brevinin1 HYba2) were identified from the skin secretion of the frog Hydrophylax bahuvistara, endemic to Western Ghats, India, and their amino acid sequences were confirmed using cDNA cloning and LC/MS/MS. Antibacterial, hemolytic, and cytotoxic activities of brevinin1 peptides and their synthetic analogs (amidated C‐terminus) were investigated and compared. All the peptides except the acidic forms showed antibacterial activity against all tested Gram‐positive and Gram‐negative bacteria. They exhibited low hemolysis on human erythrocytes and showed potent cytotoxic activity against Hep 3B cancer cell line. Upon amidation, the peptides showed increased activity against the tested microbes without altering their hemolytic and cytotoxic properties. The study also emphasizes the need for screening endemic amphibian fauna of Western Ghats, as a potential source of host defense peptides with possible therapeutic applications in the future.     

Design of potent, non-toxic antimicrobial agents based upon the naturally occurring frog skin peptides, ascaphin-8 and peptide XT-7

The frog skin peptides, ascaphin-8 (GFKDLLKGAAKALVKTVLF.NH(2)) and XT-7 (GLLGPLLKIAAKVGSNLL.NH(2)), show broad-spectrum antimicrobial activity but their therapeutic potential is limited by toxicity against mammalian cells. Circular dichroism spectra demonstrate that the peptides adopt an amphipathic alpha-helical conformation in a membrane-mimetic solvent. This study has investigated the cytolytic properties of analogs containing selected amino acid substitutions that increase cationicity while maintaining amphipathicity. Substitutions at Ala(10), Val(14), and Leu(18) in ascaphin-8 by either L-Lys or D-Lys produced peptides that retained antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus and the opportunistic yeast pathogen, Candida albicans but showed appreciably reduced toxicities (>10-fold) against human erythrocytes, HepG2 hepatoma-derived cells, and L929 fibroblasts. The improved therapeutic index of the L-Lys(18) and D-Lys(18) analogs correlated with a decrease in % helicity and in effective hydrophobicity. Substitution of Gly(4) by L-Lys in XT-7 produced an analog with high potency against micro-organisms (MIC < or = 25 microM) but low cytolytic activity against erythrocytes (LD(50) > 500 microM) and this increase in therapeutic index also correlated with decreased helicity and hydrophobicity. Analogs of XT-7 with increased cationicity, containing multiple substitutions by L-Lys, not only displayed increased antimicrobial potencies, particularly against Candida albicans (MIC < or = 6 microM), but also increased hemolytic activities.     

Purification and Modeling Amphipathic Alpha Helical Antimicrobial Peptides from Skin Secretions of Euphlyctis cyanophlyctis

Antimicrobial peptides as ancient immune system are found in almost all types of living organisms. Amphibian's skin is an important source of bioactive peptides with strong antibacterial, antiviral, and antitumor properties. They have important role in inducing apoptosis as well as cancer therapy in vitro. In this study, we extracted and purified antimicrobial peptides from skin secretions of Euphlyctis cyanophlyctis and named them brevinin‐Eu and cyanophlyctin β. They showed favorable antibacterial properties on both Gram‐positive and Gram‐negative bacteria with ignorable hemolytic activity of <1.9% and 0.7% at very high concentrations of brevinin‐Eu and cyanophlyctin β, respectively. For antibacterial activity and MIC determination, two Gram‐positive (Staphylococcus aureus PTCC1431 and B. cereus PTCC1247) and two Gram‐negative bacteria (Escherichia coli HP101BA 7601c and Klebsiella pneumoniae PTCC1388) were assayed. MIC values of extracted peptides demonstrated that they can inhibit bacterial growth at very low concentration (17 and 12 μg/mL) for brevinin‐Eu and cyanophlyctin β, respectively. Structural prediction suggested that the brevinin‐Eu can efficiently bind and destroy bacterial membrane, but cyanophlyctin β uses a diverse mode of action.     

Two antimicrobial peptides from skin secretions of Rana grahami.

Two antimicrobial peptides manifested a broad spectrum of antimicrobial activity against various microorganisms have been isolated from skin secretions of Rana grahami. These antimicrobial peptides were named grahamin 1 and grahamin 2. Their primary structures are GLLSGILGAGKNIVCGLSGLC and GLLSGILGAGKHIVCGLSGLC, respectively, determined by Edman degradation and mass spectrometry. They are structurally related to nigrocins identified from skin secretions of the dark-spotted frog, Rana nigromaculata. The cDNA clones encoding the precursor of grahamins were screened and sequenced from the skin cDNA library of R. grahami. The amino sequences deduced from the cDNA sequences match well with the results from Edman degradation. As other antimicrobial peptides from Rana species, grahamins contain a C-terminal loop region delineated by an intra-disulfide bridge named Rana box. Based on structural comparison of grahamin with other known antimicrobial peptides, grahamins could be classified into the family of antimicrobial peptides containing a single intra-disulfide bridge.     

大鲵皮肤分泌液中抗菌肽的鉴定及生物活性研究

目的鉴定大鲵皮肤分泌液中抗菌肽,研究其部分生物活性。方法 5%醋酸浸提和Sephadex G-50、G-25凝胶过滤色谱等方法分离纯化抗菌肽;采用抑菌圈法检测抗菌活性,Tricine-SDS-PAGE电泳和等电聚焦电泳鉴定其抗菌活性成份。结果大鲵皮肤分泌液中含有抗菌活性物质。对革兰阴性菌、革兰阳性菌和真菌均具有较强的抗菌活性;电泳检测显示该小分子多肽相对分子质量约为4 300,具有较强的碱性。结论首次从大鲵皮肤分泌液中分离纯化到一种抗菌肽,此抗菌肽可能是一个具有较强阳离子特征的碱性肽。     

Antimicrobial Properties of Brevinin‐2‐Related Peptide and its Analogs: Efficacy Against Multidrug‐Resistant Acinetobacter baumannii

Brevinin‐2 related peptide (B2RP; GIWDTIKSMG¹⁰KVFAGKILQN²⁰L.NH₂), first isolated from skin secretions of the mink frog Lithobates septentrionalis, shows broad‐spectrum antimicrobial activity but its therapeutic potential is limited by moderate hemolytic activity. The peptide adopts an α‐helical conformation in a membrane‐mimetic solvent but amphipathicity is low. Increasing amphipathicity together with hydrophobicity by the substitutions Lys¹⁶→Leu and Lys¹⁶→Ala increased hemolytic activity approximately fivefold without increasing antimicrobial potency. The substitution Leu¹⁸→Lys increased both cationicity and amphipathicity but produced decreases in both antimicrobial potency and hemolytic activity. In contrast, increasing cationicity of B2RP without changing amphipathicity by the substitution Asp⁴→Lys resulted in a fourfold increase in potency against Escherichia coli [minimal inhibitory concentration (MIC) = 6 μm ) and twofold increases in potency against Staphylococcus aureus (MIC = 12.5 μm ) and Candida albicans (MIC = 6 μm ) without changing significantly hemolytic activity against human erythrocytes (LC₅₀ = 95 μm ). The emergence of antibiotic‐resistant strains of the Gram‐negative bacterium Acinetobacter baumannii constitutes a serious risk to public health. B2RP (MIC = 3–6 μm ) and [Lys⁴]B2RP (MIC = 1.5–3 μm ) potently inhibited the growth of nosocomial isolates of multidrug‐resistant Acinetobacter baumannii. Although the analogs [Lys⁴, Lys¹⁸]B2RP and [Lys⁴, Ala¹⁶, Lys¹⁸]B2RP showed reduced potency against Staphylococcus aureus, they retained activity against Acinetobacter baumannii (MIC = 3–6 μm ) and had very low hemolytic activity (LC₅₀ > 200 μm ).     

Peptides with antimicrobial activity of the brevinin-1 family isolated from skin secretions of the southern leopard frog,Rana sphenocephala

Abstract: Three peptides with growth-inhibitory activity towards the Gram-negative bacterium Eschericia coli were isolated from electrically stimulated secretions from the skin of the southern leopard frog, Rana sphenocephala. Structural characterization demonstrated that the peptides [brevinin-1Sa, minimum inhibitory concentration (MIC) = 55µm ; brevinin-1Sb, MIC = 17 µm ; brevinin-1Sc, MIC = 14 µm ] represent new members of the brevinin-1 family of antimicrobial peptides, previously isolated from several other species of frogs of the genus Rana. Their high concentration in skin secretions and extreme variability in amino acid sequence suggest that the brevinin family of peptides may be of value as molecular markers for the identification and taxonomic classification of Ranid frogs.     

Disulfide engineering on temporin‐SHf: Stabilizing the bioactive conformation of an ultra‐short antimicrobial peptide

In Silico searching for short antimicrobial peptides has revealed temporin‐SHf as the short (8AA), hydrophobic, broad spectrum, and natural antimicrobial peptide. Important drawback associated with temporin‐SHf is the susceptibility of its bioactive conformation for denaturation and proteolytic degradation. In the current report, disulfide engineering strategy has been adopted to improve the stability of bioactive conformation of temporin‐SHf. The functionally non‐critical Leu4 and Ile7 residues at i and i + 3 position of helical conformation of temporin‐SHf were mutated with cysteine disulfide. Designed [L4C, I7C]temporin‐SHf was synthesized, characterized using NMR spectroscopy, and accessed for antimicrobial activity. [L4C, I7C]Temporin‐SHf adopts helical conformation from Phe3 to Phe8 in the absence of membrane‐mimetic environment and retains broad spectrum antimicrobial activity. The reduction potential of cysteine disulfide of [L4C, I7C]temporin‐SHf is ?289 mV. Trypsin‐induced digestion and serum‐induced digestion have confirmed the advantage of cysteine disulfide in imparting proteolytic stability to temporin‐SHf. Disulfide‐stabilized temporin‐SHf may serve as a good model for the rational design of temporin‐SHf based antibiotics for treatment of infectious diseases.     

Modification Strategy of D-leucine Residue Addition on a Novel Peptide from Odorrana schmackeri,with Enhanced Bioactivity and In Vivo Efficacy

Brevinins are a well-characterised, frog-skin-derived, antimicrobial peptide (AMP) family, but their applications are limited by high cytotoxicity. In this study, a wild-type des-Leu2 brevinin peptide, named brevinin-1OS (B1OS), was identified from Odorrana schmackeri. To explore the significant role of the leucine residue at the second position, two variants, B1OS-L and B1OS-D-L, were designed by adding L-leucine and D-leucine residues at this site, respectively. The antibacterial and anticancer activities of B1OS-L and B1OS-D-L were around ten times stronger than the parent peptide. The activity of B1OS against the growth of Gram-positive bacteria was markedly enhanced after modification. Moreover, the leucine-modified products exerted in vivo therapeutic potential in an methicillin-resistant Staphylococcus aureus (MRSA)-infected waxworm model. Notably, the single substitution of D-leucine significantly increased the killing speed on lung cancer cells, where no viable H838 cells survived after 2 h of treatment with B1OS-D-L at 10 μM with low cytotoxicity on normal cells. Overall, our study suggested that the conserved leucine residue at the second position from the N-terminus is vital for optimising the dual antibacterial and anticancer activities of B1OS and proposed B1OS-D-L as an appealing therapeutic candidate for development.     

Design of potent, non-toxic antimicrobial agents based upon the structure of the frog skin peptide, temporin-1CEb from Chinese brown frog, Rana chensinensis

Temporin‐1CEb shows antimicrobial activity against Gram‐positive bacteria, but its therapeutic potential is limited by its haemolysis. In this study, eight temporin‐1CEb analogues with altered cationicities and hydrophobicities were synthesized. Increasing cationicity and amphipathicity by substituting neutral and non‐polar amino acid residues on the hydrophilic face of the α‐helix by five or six lysines increased antimicrobial potency approximately 10‐fold to 40‐fold, although when the number of positive charges was increased from +6 to +7, the antimicrobial potency was not additionally enhanced. The substitution of an l ‐lysine with a d ‐lysine, meanwhile maintaining the net charge and the mean hydrophobicity values, had only a minor effect on its antimicrobial activity, whereas significantly led a decrease in its haemolytic activity. Of all the peptides, l ‐K6 has the best potential as an antimicrobial agent because its antimicrobial activity against both Gram‐positive and Gram‐negative bacteria is substantial, and its haemolytic activity is negligible. l ‐K6 adopts an α‐helix in 50% trifluoroethanol/water and 30 mm SDS solutions. l ‐K6 killed 99.9% of E. coli and S. aureus at 4× MIC in 60 min, and its postantibiotic effect was >5 h. l ‐K6 affects the integrity of E. coli and S. aureus plasma membranes by rapidly inducing membrane depolarization.     

Design,synthesis, and antimicrobial activities of novel functional peptides against Gram‐positive and Gram‐negative bacteria

The extensive use of antibiotics in medicine results in the multidrug resistance of bacteria, making the development of new antimicrobial agents an urgent need. Antimicrobial peptides (AMPs) are considered as a new class of antibiotic with characteristics including an ability to kill target cells rapidly and a broad spectrum of activity. We have developed a potent antimicrobial peptide MAP‐0403 (MIC = 5 μM), but it exhibited a high hemolytic side‐effect (70.7%). To reduce its hemolytic effect and increase antimicrobial activity, three peptides derivatives of MAP‐0403 (J‐1, J‐2, and J‐3) were designed, synthesized by solid phase synthesis, purified by RP‐HPLC, and characterized by MALDI‐TOF MS. Structure–activity relationships of these peptides were studied by using circular dichroism and antimicrobial assays. The percentage of helical structure in J‐1, J‐2, and J‐3 was lower than that of MAP‐0403. The antimicrobial activity of J‐1 was the same as that of MAP‐0403 (MIC = 5 μM), J‐2 exhibited the highest activity (MIC = 2.5 μM), while J‐3 showed decreased activity (MIC = 10 μM). Compared to MAP‐0403, J‐2 showed significantly reduced hemolytic effect (3.4%), while J‐1 and J‐3 showed slightly decreased hemolytic effect (46.2%, 55.6%, respectively). Peptide J‐2 was discovered as a novel and potent antimicrobial agents.     

Antimicrobial peptide from the skin secretion of the frog Leptodactylus syphax.

Antimicrobial peptides are considered part of the innate immune system of the majority of living organisms. Most of these molecules are small, cationic and show amphiphilic nature. The skin secretions of Leptodactylus syphax were extracted by mild electrical stimulation and its semipreparative reverse-phase chromatography was resolved in more than 40 fractions. Among these fractions, an antimicrobial peptide was isolated and its amino acid sequence determined by de novo sequencing. Six other truncated forms were characterized in skin secretion. The longest one (25 amino acid residues), named syphaxin (SPX), is amidated at the C-terminal, and shares strong sequence similarity with antimicrobial peptides found in the skin secretion of leptodactylid frogs. Two of the truncated peptides (SPX(1-22) and SPX(1-16)) were tested against Escherichia coli and Staphylococcus aureus, showing low minimal inhibitory concentration (MIC) and no significant toxicity towards blood cells, including both leukocytes and erythrocytes, based on their direct incubation in whole blood at the highest MIC concentration (64 microg/mL).     

AaeAP1 and AaeAP2: Novel Antimicrobial Peptides from the Venom of the Scorpion,Androctonus aeneas: Structural Characterisation,Molecular Cloning of Biosynthetic Precursor-Encoding cDNAs and Engineering of Analogues with Enhanced Antimicrobial and Anticancer Activities

The main functions of the abundant polypeptide toxins present in scorpion venoms are the debilitation of arthropod prey or defence against predators. These effects are achieved mainly through the blocking of an array of ion channel types within the membranes of excitable cells. However, while these ion channel-blocking toxins are tightly-folded by multiple disulphide bridges between cysteine residues, there are additional groups of peptides in the venoms that are devoid of cysteine residues. These non-disulphide bridged peptides are the subject of much research interest, and among these are peptides that exhibit antimicrobial activity. Here, we describe two novel non-disulphide-bridged antimicrobial peptides that are present in the venom of the North African scorpion, Androctonus aeneas. The cDNAs encoding the biosynthetic precursors of both peptides were cloned from a venom-derived cDNA library using 3''- and 5''-RACE strategies. Both translated precursors contained open-reading frames of 74 amino acid residues, each encoding one copy of a putative novel nonadecapeptide, whose primary structures were FLFSLIPSVIAGLVSAIRN and FLFSLIPSAIAGLVSAIRN, respectively. Both peptides were C-terminally amidated. Synthetic versions of each natural peptide displayed broad-spectrum antimicrobial activities, but were devoid of antiproliferative activity against human cancer cell lines. However, synthetic analogues of each peptide, engineered for enhanced cationicity and amphipathicity, exhibited increases in antimicrobial potency and acquired antiproliferative activity against a range of human cancer cell lines. These data clearly illustrate the potential that natural peptide templates provide towards the design of synthetic analogues for therapeutic exploitation.     

Synthesis and characterization of the colistin peptide polymyxin E1 and related antimicrobial peptides

Abstract: Two strategies were developed to synthesize the acylated cyclic peptides know as polymyxins. Synthesis of polymyxin E1 and several analogs enabled us to evaluate the minimum inhibitory concentration of individual compounds against Gram‐negative bacteria. In this study we also report the first identification of two component peptides in the complex polymyxin fermentation product colistin, a Thr2Ser isoform and an acyl group isomer. Both of these peptides, as well as a known component peptide, Leu7Ile, were similar to polymyxin E1 in potency, suggesting that conservative mutations in the colistin family are functionally inconsequential. In contrast, the acyclic analogs of all of these peptides were inactive, indicating that the characteristic lariat structure of the polymyxins is necessary for antimicrobial activity.     

Hydrophobic interactions in complexes of antimicrobial peptides with bacterial polysaccharides

Biofilms of Pseudomonas aeruginosa are responsible for chronic lung infections in cystic fibrosis patients, where they are characterized by overproduction of the exopolysaccharide alginate and are recalcitrant to treatment with conventional antibiotics. Cationic antimicrobial peptides (CAPs) are potential alternatives for the treatment of multi-drug-resistant P. aeruginosa. However, alginate in P. aeruginosa biofilms has been proposed to bind these peptides through hydrophobic interactions, consequently reducing their activity [Chan et al., J Biol Chem 2004; 279: 38749-38754]. Here we perform biophysical analyses of the interactions of alginate with a series of novel peptide antibiotics (alpha-CAPs) of prototypic sequence KK-AAAXAAAAAXAAWAAXAAA-KKKK (where X = Phe, Trp or Leu). The hydrophobic interaction interface in alginate was investigated by examining (i) the effects of polysaccharide composition with respect to D-mannuronate and L-guluronate content; (ii) glycan chain length; (iii) alpha-CAP Trp fluorescence; and (iv) 1-anilinonaphthalene-8-sulfonate fluorescence. The results show that, while M and G residues produce equivalent effects, hydrophobic interactions between alginate and alpha-CAPs require a minimal glycan chain length. Peptide interactions with alginate are deduced to be mediated by hydrophobic microdomains comprised of pyranosyl C-H groups that are inducible upon formation of alpha-CAP-alginate complexes due to charge neutralization between the two species.     

Simplified,serine‐rich theta‐defensin analogues as antitumour peptides

θ‐defensins belong to the family of host defence peptides. They are the only known example of cyclic polypeptides in animal proteomes. This study presents the synthesis of simplified θ‐defensin analogues with pairs of cysteine replaced either by alanine, leucine or serine residues. Cytotoxicity tests were performed on human mammary epithelial (HB2) and breast cancer (SKBR3, MDA‐MB‐231) cell lines to determine whether peptides are selectively targeting cancer cells. The effect of these peptides was also evaluated in 3D Matrigel cultures, which are based on extracellular matrix components and therefore closely represent in vivo conditions. Finally, to determine whether analogues are able to sensitize MDA‐MB‐231 triple‐negative breast cancer cells to chemotherapeutics, we co‐administrated peptides with cisplatin or doxorubicin hydrochloride also in 3D Matrigel cultures. Additionally, cytotoxicity towards peripheral blood mononuclear cells and haemolytic effect were examined for a chosen representative of synthesized compounds. The results showed that positively charged serine‐containing θ‐defensin derivatives were more cytotoxic towards breast cancer cells (SKBR3, MDA‐MB‐231) than towards mammary epithelial cells (HB2). Analogues enhanced the effect of cisplatin and doxorubicin hydrochloride on triple‐negative breast cancer cell line (MDA‐MB‐231).     

Stability of Antimicrobial Decapeptide (KSL) and Its Analogues for Delivery in the Oral Cavity

Purpose To investigate the stability of KSL, an antimicrobial decapeptide, and its analogues, in human saliva and simulated gastric fluid for delivery in the oral cavity. Materials and Methods The degradation products of KSL in human saliva and simulated gastric fluid were separated by reversed-phase HPLC and their structures were identified by electrospray ionization-mass spectrometry. Analogues of KSL were synthesized by solid-phase synthesis procedure. Their enzymatic stabilities and antimicrobial activities were studied. Results KSL was degraded by the peptide bond cleavages at Lys⁶–Val⁷ in the human saliva and Phe⁵–Lys⁶ in simulated gastric fluids. Three analogues of KSL were synthesized; the Lys⁶ residue was either methylated (KSL-M), or replaced with Trp (KSL-W), or the d-form of Lys (KSL-D). The KSL analogues were much more stable than the native KSL, with the rank order of stability being KSL-D > KSL-W > KSL-M > KSL in human saliva. However, in simulated gastric fluid, while KSL-D was still stable, KSL-W was significantly degraded. In addition, KSL-D significantly lost the antimicrobial activity, whereas KSL-W completely preserved the activity against several oral bacteria. In a chewing gum formulation, KSL-W showed a more sustained release profile as compared with the native KSL. Conclusion This study suggests that KSL-W could be used as an antiplaque agent in a chewing gum formulation.     

Effects of Hydrophobicity on the Antifungal Activity of α‐Helical Antimicrobial Peptides

We utilized a series of analogs of D‐V13K (a 26‐residue amphipathic α‐helical antimicrobial peptide, denoted D1) to compare and contrast the role of hydrophobicity on antifungal and antibacterial activity to the results obtained previously with Pseudomonas aeruginosa strains. Antifungal activity for zygomycota fungi decreased with increasing hydrophobicity (D‐V13K/A12L/A20L/A23L, denoted D4, the most hydrophobic analog was sixfold less active than D1, the least hydrophobic analog). In contrast, antifungal activity for ascomycota fungi increased with increasing hydrophobicity (D4, the most hydrophobic analog was fivefold more active than D1). Hemolytic activity is dramatically affected by increasing hydrophobicity with peptide D4 being 286‐fold more hemolytic than peptide D1. The therapeutic index for peptide D1 is 1569‐fold and 62‐fold better for zygomycota fungi and ascomycota fungi, respectively, compared with peptide D4. To reduce the hemolytic activity of peptide D4 and improve/maintain the antifungal activity of D4, we substituted another lysine residue in the center of the non‐polar face (V16K) to generate D5 (D‐V13K/V16K/A12L/A20L/A23L). This analog D5 decreased hemolytic activity by 13‐fold, enhanced antifungal activity to zygomycota fungi by 16‐fold and improved the therapeutic index by 201‐fold compared with D4 and represents a unique approach to control specificity while maintaining high hydrophobicity in the two hydrophobic segments on the non‐polar face of D5.