送交者: 红旗飘飘 于 2006-1-24, 10:03:10:
丘 教 授可能 对 抗 生 素 不 了一定 了 解因此 贴 了一文章 给 他。读 完此文以后，更是 觉 得丘 教 授 可能 部分 改了 数 据。比如 说colicin Ia其实就是 类似 ionphore antibiotics，因为它本身就可以 插 入
到 Cell Membrane 中，其所以 没有抗 Staphylococcus aureus 活性可能是由于 它 不能 通 过细 胞壁的
原因，你能相信加上了那 个玩艺儿它 就能 过？
Antimicrobial Agents and Chemotherapy, August 2005, p. 3114-3121, Vol. 49, No. 8
Functional Interrelationships between Cell Membrane and Cell Wall in Antimicrobial Peptide-Mediated Killing of Staphylococcus aureus
Yan Q. Xiong,1,2,3*, Kasturi Mukhopadhyay, Michael R. Yeaman,1,2,3 Jill Adler-Moore,4 and Arnold S. Bayer1,2,3
The LA Biomedical Research Institute at Harbor—UCLA, Torrance, California,1 Department of Medicine, Harbor—UCLA Medical Center, Torrance, California,2 The David Geffen School of Medicine at UCLA, Los Angeles, California,3 Department of Microbiology, California Polytechnical State University at Pomona, Pomona, California4
ABSTRACT
Perturbation of the Staphylococcus aureus cytoplasmic membrane (CM) is felt to play a key role in the microbicidal mechanism of many antimicrobial peptides (APs). However, it is not established whether membrane permeabilization (MP) alone is sufficient to kill susceptible staphylococci or if the cell wall (CW) and/or intracellular targets contribute to AP-induced lethality. We hypothesized that the relationships between MP and killing may differ for distinct APs. In this study, we investigated the association between AP-induced MP and lethality in S. aureus whole cells versus CW-free protoplasts, and in comparison to the MP of liposomes modeled after whole CMs in terms of phospholipid composition, fluidity and charge. Four APs with different structure-activity relationships were examined: thrombin-induced platelet microbicidal protein 1 (tPMP-1), human neutrophil protein 1 (hNP-1), gramicidin D, and polymyxin B. MP was quantified fluorometrically by calcein release. All APs tested, except polymyxin B, caused concentration-dependent MP and killing of whole cells, but not of protoplasts. The reduced AP susceptibility of protoplasts was associated with increased cardiolipin and lysyl-phosphatidylglycerol content and reduced fluidity of their CMs. However, liposomal MP induced by tPMP-1, hNP-1, and gramicidin D paralleled that of whole cells. Collectively, these results indicate that (i) structurally distinct APs likely exert their staphylocidal effects by differing mechanisms, (ii) MP is not the sole event leading to AP-induced staphylocidal activity, (iii) a complex interrelationship exists between the CM and CW in AP-induced killing, and (iv) liposomes modeled upon whole cell or protoplast CMs can recapitulate the respective susceptibilities to killing by distinct APs.
Introduction: Endogenous antimicrobial peptides (APs) are believed to play a major role in innate host defense against infection in species ranging from invertebrates to humans. Despite considerable variation in composition, structure, charge, and putative mechanism(s) of action, many APs appear to initially interact with and perturb microbial cytoplasmic membranes (CMs) (50). Recent data have suggested that the microbial cell wall (CW) may also be involved in AP-induced microbicidal pathways (39). However, the relative contributions of CM, CW, and other targets beyond these sites (e.g., intracellular targets in the lethal mechanisms of APs have not been clearly established.
Over the last decade, a number of target CM characteristics have been shown to impact the in vitro activity of APs against microbial cells, including fatty acid and phospholipid content, CM fluidity, and transmembrane potential. In addition, such parameters appear to influence AP activity in artificial model membrane systems (i.e., membrane vesicles and planar lipid bilayers). Likewise, CW characteristics have been shown to affect AP susceptibility in selected organisms (e.g., Staphylococcus aureus). However, few studies have investigated the relationship among the CM, CW, and microbicidal mechanisms of APs differing in structure and activity.
In the present study, we investigated AP-induced membrane permeabilization (MP) and killing in S. aureus whole cells versus CW-free protoplasts. In addition, liposomes were strategically designed to simulate the S. aureus CM. For these analyses, four different CM-targeting APs were selected on the basis of their diverse sources (mammalian, bacterial), structures, and putative mechanisms of action: thrombin-induced platelet microbicidal protein 1 (tPMP-1), human neutrophil peptide 1 (hNP-1), gramicidin D, and polymyxin B. The goals of this investigation were threefold: (i) to delineate the relationships between MP and killing among different APs, (ii) to characterize the CW contributions to AP-induced S. aureus killing, and (iii) to assess whether AP-induced MP in whole cells can be modeled in strategic liposomes. Our results indicated that distinct interrelationships exist between CM, CW, and killing of S. aureus by the individual APs studied. Moreover, use of whole cells, protoplasts, and liposomes provided complementary insights into AP-S. aureus interactions.