China 
Africa 
Explore chapters and articles related to this topic
pH-Responsive Polymers for Delivery of Nucleic Acid Therapeutics
Published in Severian Dumitriu, Valentin Popa, Polymeric Biomaterials, 2020
pH-specific fusogenic or lytic peptides do not have high efficiency at any cases. Various peptides have been compared for the promotion of polyplex-based gene transfer (Futaki et al. 2005; Lim et al. 2000; Wagner 1999). Results showed that the improvement also depends on the characteristics of the cationic carriers. Peptide HA-2 and other synthetic or natural sequences such as the amphipathic peptides GALA, KALA, EGLA, JTS1, and gramicidin S have been tested. Introduction of membrane-active peptides in ligand-PLL-mediated gene delivery could improve the transfection up to more than 1000-fold. Whereas other PCs like dendrimers or PEI as well as several cationic lipids are only slightly enhanced by endosomolytic peptides or adenoviruses, clearly demonstrating differences in the bottlenecks of the delivery processes. Electroneutral cationic lipid–DNA complexes however can be strongly improved by the addition of membrane-active peptides.
Enzyme Catalysis
Published in Harvey W. Blanch, Douglas S. Clark, Biochemical Engineering, 1997
Harvey W. Blanch, Douglas S. Clark
The rate of growth of the cell population X1+X2 follows a Monod-type dependence on substrate (S), while the rate of product formation is assumed to be proportional to the number of mature cells. The cell yield coefficient is 1/γ, and the rate of product formation is proportional to the rate of formation of mature cells. This model can simulate the production kinetics of the cyclic decapeptide gramicidin S, a bacterial antibiotic produced by Bacillus brevis. Gramicidin S synthetase activity increases dramatically in the late logarithmic phase of growth, resulting in gramicidin S production in the late logarithmic and stationary phases of growth. The kinetics of growth and product formation are illustrated in Figure 3.30.
Bacillus subtilis ME22 and Its Application to Biological Control
Published in Yoshikatsu Murooka, Tadayuki Imanaka, Recombinant Microbes for Industrial and Agricultural Applications, 2020
Although the biosynthetic pathway for iturin production has not yet been studied, it is postulated that it is synthesized through nonribosomal mechanism, similar to most of the polypeptide antibiotics, such as gramicidin S, tyrocidine, and bacitracin [35,36], because it contains residues of d-α-amino acids in its structure. In our preliminary experiments on the biosynthetic enzymes of iturin, an ATP-inorganic orthophosphate (Pi)-exchange reaction was suggested (unpublished observation), which has been found in the biosyntheses of mycobacillin, and surfactin [40,41].
Studies on a new antimicrobial peptide from Vibrio proteolyticus MT110
Published in Preparative Biochemistry & Biotechnology, 2023
Himanshu Verma, Kanti N. Mihooliya, Jitender Nandal, Debendra K. Sahoo
Antimicrobial peptides (AMPs) are short-cationic and amphiphilic molecules because of hydrophobic and positively charged residues, and some of these AMPs are known to exhibit immunomodulatory activity.[1,2] Many naturally occurring AMPs are found in diverse forms of life (e.g., http://aps.unmc.edu/AP/main.php), and being a part of the innate immune system, these peptides are also called natures antibiotics.[3] AMPs, though produced by every form of life, show immense diversity in sequence and antimicrobial activity because of differences in the pathogenic challenges and virulence strategy the producer organisms face. Generally, AMPs show broad-spectrum activity against Gram-positive and Gram-negative bacteria, viruses, parasites, and fungi. However, only a few AMPs are used for medicinal purposes (such as polymyxin B and gramicidin S) because of their broad-spectrum and weakened antimicrobial activity under physiological conditions.[1,4]
The purification and functional study of new compounds produced by Escherichia coli that influence the growth of sulfate reducing bacteria
Published in Egyptian Journal of Basic and Applied Sciences, 2020
Oluwafemi Adebayo Oyewole, Julian Mitchell, Sarah Thresh, Vitaly Zinkevich
Several studies have described some inhibitors of SRB growth that are derived from bacteria; for example, Jayaraman et al. [69] and Zuo [29] reported that indolicidin, bactenecin, and polymyxin produced by Paenibacillus polymyxa are capable of inhibiting SRB growth. Bacillus brevis produces a compound referred to as gramicidin-S that inhibits the growth of Desulfovibrio orientis, D. vulgaris and D. gigas [29,31,70] and thereby reduced corrosion caused by the SRB. In addition, Bacillus licheniformis secretes γ-polyglutamate and polyaspartate that reduce SRB growth [29,71,72]. The mechanism of SRB growth prevention by these organisms has been suggested and include either the production of antimicrobial agents [29,73] or attack on the adenosine 5ʹ- phosphosulphate (APS) and bisulfate reductase (DSR) responsible for hydrogen sulfide production in SRBs [14]. Similarly, the SGE may function in SRB induction by increasing their growth rate while the SGI may function by causing damage in the cells as observed in this study. The MALDI-TOF spectra showed the presence of low molecular weight compounds in the range of 1700 Da for SGE and 2400 Da for SGI. The spectra showed equal and repeating units of ~213 m/z between the peaks. According to Wallace and Guttman [74], the equal and repeating units are characteristic spectra of condensation homopolymers. MALDI-TOF spectra revealed that the compounds are small molecular weight biomolecules and that the two molecules are very closely related.
Effect of glutamic acid elimination/substitution on the biological activities of S3 cationic amphiphilic peptides
Published in Preparative Biochemistry & Biotechnology, 2020
Mina Sepahi, Reza Ahangari Cohan, Shahin Hadadian, Dariush Norouzian
Improved binding affinity to LPS could be the reason for decreased MIC values of new variants. Most of studies related to AMP modifications have been performed by increasing the positive charges of AMPS by substitution amino acids by lysine or arginine. Unfortunately, increasing the amounts of lysine or arginine affects the cytotoxicity of CAPs directly. Kondejewski and coworkers studied the effect of adding lysine and cyclic residues to gramicidin S antimicrobial peptide (GS). The new analogs had higher positive charge, higher endotoxin neutralization activity, higher amphipathicity, and higher hemolytic activity. Then, they could restrict the amphipathicity by substitution of D-enantiomers of some residues. In this case, they reached to the same antimicrobial activity with lower hemolytic effects.[36] Colon and coworkers reported the same effects for analogs of alyteserin-2a antimicrobial peptide derived from the frog skin. They enhanced the charge of this peptide by substitution of glycine with L-lysine and observed higher antimicrobial activities, higher amphipathicity and hence higher hemolytic properties.[37] Tan and coworkers enhanced the positive charge of the S3 peptide by replacing its G276 and E278 with lysine. The modified variant (SΔ3) showed stronger LPS neutralization activity, a minor enhanced LPS binding affinity,[12] conserved antimicrobial, and higher hemolytic (3.6-fold) activities than S3 peptide.[17] Other similar studies have also reported a direct relationship between hydrophobicity and amphipathicity with antimicrobial activity and hemolytic property.[9,26,36,38,39] The risk of hemolysis usually restricts applications of CAPs for clinical or even biotechnological purposes. In this research, S3 peptide was successfully modified while conserving its low hemolytic activity. Hemolytic activities of S3 peptide and its new variants at 500 µg/ml concentration were less than 25%, as a threshold for risk of hemolytic property[32] and were also less than the hemolysis activity of SΔ3 (37% hemolysis at 100 µg/ml).[17] S3E3 was the best-modified variant with 68.5% higher LPS binding affinity and 40.4% lower MIC, and conserved hemolytic activity compared to S3. Our findings revealed that slightly increasing of mean hydrophobicity did not have any undesirable effect on hemolytic activity.