Abstract. A motivational community visualization was designed to encourage users to participate more actively and to bring more contributions in an online community. The visualization is inspired by the theory of social comparison in social psychology. It evolved through two designs: a fixed and a customizable one for two different communities of students sharing papers -one of graduate students in a research lab and another one for students in an undergraduate class. The paper discusses the features of the two communities, each of the two visualization designs, their advantages and disadvantages.
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 a-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 a-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.Key words: cationicity, depolarization, haemolytic activity, hydrophobicity, membrane integrity Received 23 May 2011, revised 9 January 2012 and accepted for publication 10 January 2012Antimicrobial peptides (AMPs) with broad-spectrum antibacterial activities are synthesized in the skins of frogs and components of the innate immune systems of frogs (1). These compounds have potential as therapeutic agents against microorganisms (2). To date, approximately 200 AMPs, belonging to more than 20 different families, have been identified from more than 40 different amphibians (3-5). Among the AMP families, the members of the temporin family are short (10-13 amino acids), hydrophobic and C-terminally amidated AMPs found in frog skin that have haemolytic activity as well as antimicrobial activity. The first temporin was identified in the skin of the Asian frog Rana erythraea on the basis of its haemolytic activity (6). More than 50 different temporins have subsequently been isolated from the skins of North American and Eurasian frogs of the genus Rana and display potent antimicrobial activity against bacteria, fungi and even certain viruses (7,8). The antimicrobial mechanism of temporins is thought to be based on the leakage of water and ions through pores in the bacterial cell membrane (9). Although the use of the naturally occurring temporin-1CEb as antibiotics is limited because of their substantial haemolytic activities against human erythrocytes, temporins modified according to amphipathicity, charge and secondary structure may still represent promising drug candidates.Temporin-1CEb is a naturally occurring 12-residue peptide derived from skin secretions of Rana amurensis (th...
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