Medical Proteomics Laboratory, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
Biochemistry. 2011 Aug 30;50(34):7311-20. doi: 10.1021/bi200493h. Epub 2011 Aug 4.
Antibiotic resistance is increasingly seen as a serious problem that threatens public health and erodes our capacity to effectively combat disease. So-called non-iron metalloporhyrins have shown promising antibacterial properties against a number of pathogenic bacteria including Staphylococcus aureus. However, little is known about the molecular mechanism(s) of action of these compounds and in particular how they reach the interior of the bacterial cells. A popular hypothesis indicates that non-iron metalloporphyrins infiltrate into bacterial cells like a "Trojan horse" using heme transport systems. Iron-regulated surface determinant (Isd) is the best characterized heme transport system of S. aureus. Herein we studied the molecular mechanism by which the extracellular heme-receptor IsdH-NEAT3 of Isd recognizes antimicrobial metalloporphyrins. We found that potent antibacterial porphyrins Ga(III)-protoporphyrin IX (PPIX) and Mn(III)-PPIX closely mimicked the properties of the natural ligand heme, namely (i) stable binding to IsdH-NEAT3 with comparable affinities for the receptor, (ii) nearly undistinghuishable three-dimensional structure when complexed with IsdH-NEAT3, and (iii) similar transfer properties to a second receptor IsdA. On the contrary, weaker antibacterial porphyrins Mg(II)-PPIX, Zn(II)-PPIX, and Cu(II)-PPIX were not captured effectively by IsdH-NEAT3 under our experimental conditions and displayed lower affinities. Moreover, reduction of Fe(III)-PPIX to Fe(II)-PPIX with dithionite abrogated stable binding to receptor. These data revealed a clear connection between oxidation state of metal and effective attachment to IsdH-NEAT3. Also, the strong correlation between binding affinity and reported antimicrobial potency suggested that the Isd system may be used by these antibacterial compounds to gain access to the interior of the cells. We hope these results will increase our understanding of Isd system of S. aureus and highlight its biomedical potential to deliver new and more efficient antibacterial treatments.
抗生素耐药性日益被视为严重威胁公众健康、削弱我们有效对抗疾病能力的问题。所谓的非铁金属卟啉对包括金黄色葡萄球菌在内的多种致病菌显示出有希望的抗菌特性。然而，人们对这些化合物的作用机制知之甚少，特别是它们如何进入细菌细胞内部。一个流行的假设表明，非铁金属卟啉通过血红素转运系统像“特洛伊木马”一样渗透到细菌细胞中。铁调节表面决定簇（Isd）是金黄色葡萄球菌中最好表征的血红素转运系统。在此，我们研究了细胞外血红素受体 IsdH-NEAT3 识别抗菌金属卟啉的分子机制。我们发现，有效的抗菌卟啉 Ga(III)-原卟啉 IX（PPIX）和 Mn(III)-PPIX 非常类似于天然配体血红素的性质，即（i）与 IsdH-NEAT3 稳定结合，对受体具有相当的亲和力，（ii）与 IsdH-NEAT3 复合时几乎无法区分三维结构，以及（iii）与第二个受体 IsdA 具有相似的转移特性。相反，在我们的实验条件下，较弱的抗菌卟啉 Mg(II)-PPIX、Zn(II)-PPIX 和 Cu(II)-PPIX 不能被 IsdH-NEAT3 有效捕获，并且显示出较低的亲和力。此外，用连二亚硫酸钠将 Fe(III)-PPIX 还原为 Fe(II)-PPIX 会破坏与受体的稳定结合。这些数据揭示了金属氧化态与有效附着到 IsdH-NEAT3 之间的明确联系。此外，结合亲和力与报道的抗菌效力之间的强相关性表明，Isd 系统可能被这些抗菌化合物用于进入细胞内部。我们希望这些结果将提高我们对金黄色葡萄球菌 Isd 系统的理解，并强调其在提供新的、更有效的抗菌治疗方面的生物医学潜力。
