Peek Mary E, Bhatnagar Abhinav, McCarty Nael A, Zughaier Susu M
School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Interdiscip Perspect Infect Dis. 2012;2012:843509. doi: 10.1155/2012/843509. Epub 2012 Sep 2.
Pseudomonas aeruginosa is the most common pathogen that persists in the cystic fibrosis lungs. Bacteria such as P. aeruginosa secrete siderophores (iron-chelating molecules) and the host limits bacterial growth by producing neutrophil-gelatinase-associated lipocalin (NGAL) that specifically scavenges bacterial siderophores, therefore preventing bacteria from establishing infection. P. aeruginosa produces a major siderophore known as pyoverdine, found to be important for bacterial virulence and biofilm development. We report that pyoverdine did not bind to NGAL, as measured by tryptophan fluorescence quenching, while enterobactin bound to NGAL effectively causing a strong response. The experimental data indicate that pyoverdine evades NGAL recognition. We then employed a molecular modeling approach to simulate the binding of pyoverdine to human NGAL using NGAL's published crystal structures. The docking of pyoverdine to NGAL predicted nine different docking positions; however, neither apo- nor ferric forms of pyoverdine docked into the ligand-binding site in the calyx of NGAL where siderophores are known to bind. The molecular modeling results offer structural support that pyoverdine does not bind to NGAL, confirming the results obtained in the tryptophan quenching assay. The data suggest that pyoverdine is a stealth siderophore that evades NGAL recognition allowing P. aeruginosa to establish chronic infections in CF lungs.
铜绿假单胞菌是在囊性纤维化肺部持续存在的最常见病原体。像铜绿假单胞菌这样的细菌会分泌铁载体（铁螯合分子），而宿主通过产生中性粒细胞明胶酶相关脂质运载蛋白（NGAL）来限制细菌生长，NGAL能特异性清除细菌铁载体，从而防止细菌建立感染。铜绿假单胞菌产生一种主要的铁载体称为绿脓菌素，已发现其对细菌毒力和生物膜形成很重要。我们报告称，通过色氨酸荧光猝灭测量发现绿脓菌素不与NGAL结合，而肠杆菌素与NGAL有效结合并引发强烈反应。实验数据表明绿脓菌素能逃避NGAL的识别。然后我们采用分子建模方法，利用已发表的NGAL晶体结构来模拟绿脓菌素与人类NGAL的结合。绿脓菌素与NGAL的对接预测出九个不同的对接位置；然而，无论是绿脓菌素的脱辅基形式还是铁离子形式都没有对接进NGAL萼部中已知铁载体结合的配体结合位点。分子建模结果为绿脓菌素不与NGAL结合提供了结构支持，证实了色氨酸猝灭试验所得结果。数据表明绿脓菌素是一种能逃避NGAL识别的隐形铁载体，使铜绿假单胞菌能够在囊性纤维化肺部建立慢性感染。
