LaCross Nathan C, Marrs Carl F, Gilsdorf Janet R
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI 48109, USA.
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI 48109, USA.
Infect Genet Evol. 2014 Aug;26:47-57. doi: 10.1016/j.meegid.2014.05.002. Epub 2014 May 10.
Nontypeable Haemophilus influenzae (NTHi) colonize the human pharynx asymptomatically, and are also an important cause of otitis media (OM). Previous studies have demonstrated that some genes are more prevalent in OM-causing NTHi strains than in commensal strains, suggesting a role in virulence. These studies, however, are unable to investigate the possible associations between gene polymorphisms and disease. This study examined amino acid polymorphisms and sequence diversity in a potential virulence gene, the hemin receptor hemR, from a previously characterized NTHi strain collection containing both commensal and OM organisms to identify possible associations between the polymorphisms and otitis media. The full open reading frame of hemR was sequenced from a total of 146 NTHi isolates, yielding a total of 47 unique HemR amino acid sequences. The predicted structure of HemR showed substantial similarity to a class of monomeric TonB dependent, ligand-gated channels involved in iron acquisition in other gram negative bacteria. Fifteen amino acid polymorphisms were significantly more prevalent at the 90% confidence level among commensal compared to OM isolates. Upon controlling for the confounding effect of population structure, over half of the polymorphism-otitis media relationships lost statistical significance, emphasizing the importance of assessing the effect of population structure in association studies. The seven polymorphisms that retained significance were dispersed throughout the protein in various functional and structural domains, including the signal peptide, N-terminal plug domain, and intra- and extracellular loops. The alternate amino acid of only one of these seven polymorphisms was more common among OM isolates, demonstrating a strong trend toward the consensus sequence among disease causing NTHi. We hypothesize that variability at these positions in HemR may result in a reduced ability to acquire iron, rendering NTHi with such versions of the gene less fit for survival in the middle ear environment.
不可分型流感嗜血杆菌（NTHi）无症状地定植于人类咽部，也是中耳炎（OM）的重要病因。先前的研究表明，某些基因在引起中耳炎的NTHi菌株中比在共生菌株中更普遍，提示其在毒力方面发挥作用。然而，这些研究无法调查基因多态性与疾病之间的可能关联。本研究检测了来自先前鉴定的包含共生菌和引起中耳炎的菌株的NTHi菌株集合中，一个潜在毒力基因——血红素受体hemR中的氨基酸多态性和序列多样性，以确定这些多态性与中耳炎之间的可能关联。从总共146株NTHi分离株中对hemR的完整开放阅读框进行测序，共产生47个独特的HemR氨基酸序列。HemR的预测结构与一类参与其他革兰氏阴性菌铁摄取的单体型TonB依赖性配体门控通道显示出高度相似性。与引起中耳炎的分离株相比，15种氨基酸多态性在共生菌中以90%的置信水平显著更普遍。在控制了群体结构的混杂效应后，超过一半的多态性与中耳炎的关系失去了统计学意义，强调了在关联研究中评估群体结构效应的重要性。保留显著性的7种多态性分布在整个蛋白质的各种功能和结构域中，包括信号肽、N端塞结构域以及细胞内和细胞外环。这7种多态性中只有一种的替代氨基酸在引起中耳炎的分离株中更常见，表明在引起疾病的NTHi中存在强烈的趋向于共有序列的趋势。我们假设HemR中这些位置的变异性可能导致铁摄取能力降低，使具有该基因此类版本的NTHi在中耳环境中生存适应性更差。
