Lewis Janina P, Plata Konrad, Yu Fan, Rosato Adriana, Anaya Cecilia
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA, USA.
The Philips Institute, Virginia Commonwealth University, Richmond, VA, USA.
Microbiology (Reading). 2006 Nov;152(Pt 11):3367-3382. doi: 10.1099/mic.0.29011-0.
Porphyromonas gingivalis, an oral bacterium associated with periodontal disease, requires haemin for growth. Although several multigenic clusters encoding haemin-uptake systems are present on the genome of P. gingivalis, little is known regarding their transcriptional organization and expression. This study identified a 23 kDa iron-regulated haemin-binding protein encoded by a larger than previously reported variant of hmuY. It was shown that the hmu locus is larger than previously reported and is composed of six genes, hmuYRSTUV, encoding a novel hybrid haemin-uptake system. The locus has an operonic organization and the transcriptional start site is located 292 bp upstream of hmuY. The data indicate that the regulation of the operon is iron-dependent. Interestingly, differential regulation within the operon was demonstrated, resulting in excess of the hmuYR message encoding the outer-membrane proteins when compared to the full-length transcript. In addition, the hmuY transcript is more prevalent than the hmuR transcript. Secondary structure analysis of the hmuYRSTUV mRNA predicted the formation of several potential stem-loops in the 5' ends of hmuR- and hmuS-specific mRNAs, consistent with the differential regulation observed. Finally, it was demonstrated that haemin binding and uptake are elevated in iron-depleted conditions and are reduced 45 % and 70 %, respectively, in an hmu-deficient strain when compared to the parental strain, indicating that the hmu locus plays a major role in haemin acquisition in P. gingivalis. Since homologues of the hmu locus were also found in Bacteroides fragilis, Bacteroides thetaiotaomicron and Prevotella intermedia, these findings may have implications for a better understanding of haemin acquisition in those organisms as well.
牙龈卟啉单胞菌是一种与牙周疾病相关的口腔细菌，其生长需要血红素。尽管牙龈卟啉单胞菌的基因组上存在几个编码血红素摄取系统的多基因簇，但对其转录组织和表达了解甚少。本研究鉴定出一种由比先前报道的hmuY变体更大的基因编码的23 kDa铁调节血红素结合蛋白。结果表明，hmu基因座比先前报道的更大，由六个基因hmuYRSTUV组成，编码一种新型的混合血红素摄取系统。该基因座具有操纵子结构，转录起始位点位于hmuY上游292 bp处。数据表明该操纵子的调节是铁依赖性的。有趣的是，操纵子内存在差异调节，与全长转录本相比，编码外膜蛋白的hmuYR信息过量。此外，hmuY转录本比hmuR转录本更普遍。hmuYRSTUV mRNA的二级结构分析预测在hmuR和hmuS特异性mRNA的5'端形成几个潜在的茎环，这与观察到的差异调节一致。最后，结果表明，在缺铁条件下血红素结合和摄取增加，与亲本菌株相比，hmu缺陷菌株中的血红素结合和摄取分别降低45%和70%，表明hmu基因座在牙龈卟啉单胞菌获取血红素中起主要作用。由于在脆弱拟杆菌、嗜热栖热菌和中间普雷沃菌中也发现了hmu基因座的同源物，这些发现可能也有助于更好地理解这些生物体中血红素的获取。
