Mokry David Z, Nadia-Albete Angela, Johnson Michael K, Lukat-Rodgers Gudrun S, Rodgers Kenton R, Lanzilotta William N
Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, USA.
Department of Chemistry, University of Georgia, Athens, GA 30602, USA.
Biochim Biophys Acta. 2014 Oct;1840(10):3058-66. doi: 10.1016/j.bbagen.2014.06.009. Epub 2014 Jun 23.
For many pathogenic microorganisms, iron acquisition represents a significant stress during the colonization of a mammalian host. Heme is the single most abundant source of soluble iron in this environment. While the importance of iron assimilation for nearly all organisms is clear, the mechanisms by which heme is acquired and utilized by many bacterial pathogens, even those most commonly found at sites of infection, remain poorly understood.
An alternative protocol for the production and purification of the outer membrane hemoglobin receptor (HmbR) from the pathogen Neisseria meningitidis has facilitated a biophysical characterization of this outer membrane transporter by electronic absorption, circular dichroism, electron paramagnetic resonance, and resonance Raman techniques.
HmbR co-purifies with 5-coordinate high spin ferric heme bound. The heme binding site accommodates exogenous imidazole as a sixth ligand, which results in a 6-coordinate, low-spin ferric species. Both the 5- and 6-coordinate complexes are reduced by sodium hydrosulfite. Four HmbR variants with a modest decrease in binding efficiency for heme have been identified (H87C, H280A, Y282A, and Y456C). These findings are consistent with an emerging paradigm wherein the ferric iron center of bound heme is coordinated by a tyrosine ligand.
In summary, this study provides the first spectroscopic characterization for any heme or iron transporter in Neisseria meningitidis, and suggests a coordination environment heretofore unobserved in a TonB-dependent hemin transporter.
A detailed understanding of the nutrient acquisition pathways in common pathogens such as N. meningitidis provides a foundation for new antimicrobial strategies.
对于许多致病微生物而言，获取铁是其在哺乳动物宿主体内定殖过程中的一项重大应激。血红素是这种环境中最丰富的可溶性铁来源。虽然铁同化对几乎所有生物体的重要性是明确的，但许多细菌病原体获取和利用血红素的机制，甚至是那些在感染部位最常见的病原体，仍知之甚少。
一种用于从病原体脑膜炎奈瑟菌中生产和纯化外膜血红蛋白受体（HmbR）的替代方案，通过电子吸收、圆二色性、电子顺磁共振和共振拉曼技术，促进了对这种外膜转运蛋白的生物物理表征。
HmbR与结合的五配位高自旋铁血红素共纯化。血红素结合位点可容纳外源性咪唑作为第六个配体，这会形成一个六配位、低自旋的铁物种。五配位和六配位复合物均被连二亚硫酸钠还原。已鉴定出四种与血红素结合效率略有降低的HmbR变体（H87C、H280A、Y282A和Y456C）。这些发现与一种新出现的模式一致，即结合的血红素的铁中心由酪氨酸配体配位。
总之，本研究为脑膜炎奈瑟菌中的任何血红素或铁转运蛋白提供了首次光谱表征，并揭示了一种迄今在依赖TonB的血红素转运蛋白中未观察到的配位环境。
详细了解脑膜炎奈瑟菌等常见病原体的营养获取途径为新的抗菌策略奠定了基础。
