DeRocco Amanda J, Yost-Daljev Mary Kate, Kenney Christopher D, Cornelissen Cynthia Nau
Department of Microbiology, Virginia Commonwealth University Medical Center, PO Box 980678, Richmond, VA 23298-0678, USA.
Biometals. 2009 Jun;22(3):439-51. doi: 10.1007/s10534-008-9179-y. Epub 2008 Dec 2.
The transferrin iron acquisition system of Neisseria gonorrhoeae consists of two dissimilar transferrin binding proteins (Tbp) A and B. TbpA is a TonB dependent transporter while TbpB is a lipoprotein that makes iron acquisition from transferrin (Tf) more efficient. In an attempt to further define the individual roles of these receptors in the process of Tf-iron acquisition, the kinetics of the receptor proteins in regards to ligand association and dissociation were evaluated. Tf association with TbpB was rapid as compared to TbpA. Tf dissociation from the wild-type receptor occurred in a biphasic manner; an initial rapid release was followed by a slower dissociation over time. Both TbpA and TbpB demonstrated a two-phase release pattern; however, TbpA required both TonB and TbpB for efficient Tf dissociation from the cell surface. The roles of TbpA and TbpB in Tf dissociation were further examined, utilizing previously created HA fusion proteins. Using a Tf-utilization deficient TbpA-HA mutant, we concluded that the slower rate of ligand dissociation demonstrated by the wild-type transporter was a function of successful iron internalization. Insertion into the C-terminus of TbpB decreased the rate of Tf dissociation, while insertion into the N-terminus had no effect on this process. From these studies, we propose that TbpA and TbpB function synergistically during the process of Tf iron acquisition and that TbpB makes the process of Tf-iron acquisition more efficient at least in part by affecting association and dissociation of Tf from the cell surface.
淋病奈瑟菌的转铁蛋白铁获取系统由两种不同的转铁蛋白结合蛋白（Tbp）A和B组成。TbpA是一种依赖TonB的转运蛋白，而TbpB是一种脂蛋白，可提高从转铁蛋白（Tf）获取铁的效率。为了进一步明确这些受体在Tf-铁获取过程中的各自作用，评估了受体蛋白在配体结合和解离方面的动力学。与TbpA相比，Tf与TbpB的结合迅速。Tf从野生型受体的解离呈双相方式；最初快速释放，随后随着时间推移解离较慢。TbpA和TbpB均表现出双相释放模式；然而，TbpA需要TonB和TbpB才能使Tf从细胞表面有效解离。利用先前构建的HA融合蛋白，进一步研究了TbpA和TbpB在Tf解离中的作用。使用Tf利用缺陷型TbpA-HA突变体，我们得出结论，野生型转运蛋白显示出的较慢配体解离速率是成功内化铁的结果。插入TbpB的C末端降低了Tf解离速率，而插入N末端对该过程没有影响。从这些研究中，我们提出TbpA和TbpB在Tf铁获取过程中协同发挥作用，并且TbpB至少部分地通过影响Tf与细胞表面的结合和解离，使Tf-铁获取过程更有效。
