Antimicrobial polypeptides such as the defensins kill a wide range of organisms, including bacteria, fungi, viruses, and tumor cells. Because of the recent finding that intestinal defensins, also known as cryptdins, are synthesized by the Paneth cells of the small intestinal crypts and released into the lumen, we asked whether defensins and other small cationic antimicrobial peptides could kill the trophozoites of Giardia lamblia, which colonize the small intestine. Four mouse cryptdins, two neutrophil defensins (HNP-1 [human] and NP-2 [rabbit]), and the unique tryptophan-rich bovine neutrophil polypeptide indolicidin each had some antigiardial activity against trophozoites in vitro. Cryptdins 2 and 3, indolicidin, and NP-2 each reduced viability by more than 3 log units in 2 h, and killing by all peptides was dose and time dependent. Exposure of trophozoites to peptides frequently resulted in cell aggregation and dramatic changes in morphology. The mechanism of binding and lysis appeared to involve charge interactions, since 150 mM NaCl as well as millimolar levels of Ca2' and Mg2' inhibited killing by most of the peptides. Our studies show that G. lamblia is sensitive to defensins and indolicidin and suggest that these small polypeptides could play a role in nonimmune host defenses.

This study addresses the molecular basis for protein kinase C's specific activation by phosphatidylserine. Specifically, we ask whether protein kinase C's phospholipid specificity arises from specific protein/lipid interactions or whether it arises from unique membrane-structuring properties of phosphatidylserine. We measured the interaction of protein kinase C betaII to membranes that differed only in being enantiomers to one another: physical properties such as acyl chain composition, membrane fluidity, surface curvature, microdomains, headgroup packing, and H-bonding with water were identical. Binding and activity measurements reveal that protein kinase C specifically recognizes 1, 2-sn-phosphatidyl-L-serine, independently of membrane structure. High-affinity binding and activation are abolished in the presence of enantiomeric membranes containing 2,3-sn-phosphatidyl-L-serine, 2, 3-sn-diacylglycerol, and 2,3-sn-phosphatidylcholine. Our data also show that the stereoselectivity for 1,2-sn-diacylglycerol is not absolute; 2,3-sn-diacylglycerol modestly increases the membrane affinity of protein kinase C provided that 1, 2-sn-phosphatidyl-L-serine is present. We also find that the stereochemistry of the bulk phospholipid, in this case phosphatidylcholine, has no significant influence on protein kinase C's membrane interaction. These data reveal that specific molecular determinants on protein kinase C stereospecifically recognize structural determinants of phosphatidylserine.

Despite the growing interest in social media and user-generated content, both academics and practitioners are struggling to understand the value and consequences of social media (e.g., blogs). This study employed a 2 (media source: mainstream/ social media) × 2 (message valence: positive/negative) × 2 (team identification: high/low) between-subjects design on source credibility and attitude toward an article. Positive and negative messages about the university’s varsity men’s basketball team were presented in either the mainstream media (sport magazine) or a user-generated format (blog). The results revealed that message valence had a significant main impact on triggering biased source evaluation and attitude toward the message. In turn, media source had a significant main effect on source expertise, but no main effects were found for trustworthiness and attitude. Team identification moderated the effect of media source on cognitive processing, suggesting that highly identified fans evaluated mainstream content more favorably, whereas less identified fans preferred user-generated content.

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