Tamura Glen S, Nittayajarn Aphakorn, Schoentag Deborah L
Children's Hospital and Regional Medical Center and the University of Washington, Seattle, Washington 98105, USA.
Infect Immun. 2002 Jun;70(6):2877-85. doi: 10.1128/IAI.70.6.2877-2885.2002.
Group B streptococci (GBS) are a leading cause of neonatal sepsis and meningitis. GBS adhere to fibronectin when it is attached to a solid phase. We isolated a Tn917 transposon mutant, COH1-GT1, which shows decreased adherence to fibronectin. COH1-GT1 also shows decreased adherence to and invasion of respiratory epithelial cells in vitro and decreased virulence in vivo. COH1-GT1 contains a Tn917 insertion in a homolog of glnQ, a gene from Escherichia coli which is required for glutamine transport and codes for a cytoplasmic ATP-binding cassette protein. To confirm that the decreased fibronectin adherence of COH1-GT1 was due to the mutation in glnQ, we constructed COH1-GT2, a strain with a nonpolar site-directed mutation in glnQ. COH1-GT2 showed decreased binding to fibronectin. We also demonstrated that complementation of glnQ in trans restored fibronectin adherence to COH1-GT1. COH1-GT1 shows decreased uptake of radiolabeled glutamine and is resistant to the toxic glutamine analog gamma-L-glutamylhydrazide, demonstrating that the glnQ gene is required for glutamine transport in GBS. glnQ lacks a signal sequence and is a cytoplasmic protein in E. coli and thus is unlikely to act as a fibronectin adhesin. glnQ is transcribed in an operon with a putative glutamine permease gene, glnP, which has a novel predicted structure containing three distinct domains linked in a single gene. The first two domains are putative glutamine binding domains with homology to the E. coli periplasmic glutamine binding gene glnH. The third is a putative permease domain with homology to the E. coli glutamine permease gene glnP. RT-PCR analysis demonstrated that glnP and glnQ are contained within a single transcript. Transcription of scpB, encoding the only known fibronectin-binding adhesin of GBS, is unaffected. We speculate that glnQ may regulate expression of fibronectin adhesins by affecting cytoplasmic glutamine levels and that regulation may be posttranscriptional.
B族链球菌（GBS）是新生儿败血症和脑膜炎的主要病因。当纤连蛋白附着于固相时，GBS会与之黏附。我们分离出了一个Tn917转座子突变体COH1-GT1，它对纤连蛋白的黏附能力下降。COH1-GT1在体外对呼吸道上皮细胞的黏附和侵袭能力也下降，并且在体内的毒力降低。COH1-GT1在谷氨酰胺转运所需的大肠杆菌基因glnQ的一个同源物中含有一个Tn917插入，该基因编码一种细胞质ATP结合盒蛋白。为了证实COH1-GT1对纤连蛋白黏附能力的下降是由于glnQ中的突变，我们构建了COH1-GT2，这是一个在glnQ中具有非极性定点突变的菌株。COH1-GT2对纤连蛋白的结合能力下降。我们还证明，通过反式互补glnQ可恢复COH1-GT1对纤连蛋白的黏附。COH1-GT1对放射性标记谷氨酰胺的摄取减少，并且对有毒的谷氨酰胺类似物γ-L-谷氨酰肼具有抗性，这表明glnQ基因是GBS中谷氨酰胺转运所必需的。glnQ缺乏信号序列，在大肠杆菌中是一种细胞质蛋白，因此不太可能作为纤连蛋白黏附素起作用。glnQ与一个假定的谷氨酰胺通透酶基因glnP在一个操纵子中转录。glnP具有一种新颖的预测结构，包含在单个基因中相连的三个不同结构域。前两个结构域是假定的谷氨酰胺结合结构域，与大肠杆菌周质谷氨酰胺结合基因glnH具有同源性。第三个是假定的通透酶结构域，与大肠杆菌谷氨酰胺通透酶基因glnP具有同源性。逆转录聚合酶链反应（RT-PCR）分析表明，glnP和glnQ包含在单个转录本中。编码GBS唯一已知的纤连蛋白结合黏附素的scpB的转录不受影响。我们推测，glnQ可能通过影响细胞质谷氨酰胺水平来调节纤连蛋白黏附素的表达，并且这种调节可能是转录后水平的。
