Department of Energy, Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Microbiology (Reading). 2010 Mar;156(Pt 3):731-741. doi: 10.1099/mic.0.035410-0. Epub 2009 Dec 3.
We have characterized a Fremyella diplosiphon TonB protein (FdTonB) and investigated its function during complementary chromatic adaptation. Sequence similarity analysis of FdTonB (571 aa) led to identification of several conserved domains characteristic of TonB proteins, including an N-terminal transmembrane domain, a central proline-rich spacer and a C-terminal TonB-related domain (TBRD). We identified a novel glycine-rich domain containing (Gly-X)(n) repeats. To assess FdTonB function, we constructed a DeltatonB mutant through homologous recombination based upon truncation of the central proline-rich spacer, glycine-rich domain and TBRD. Our DeltatonB mutant exhibited an aberrant cellular morphology under green light, with expanded cell width compared to the parental wild-type (WT) strain. The cellular morphology of the DeltatonB mutant recovered upon WT tonB expression. Interestingly, tonB expression was found to be independent of RcaE. As DeltatonB and WT strains respond in the same way when grown under iron-replete versus iron-limited conditions, our results suggest that FdTonB is not involved in the classic TonB function of mediating cellular adaptation to iron limitation, but exhibits a novel function related to the photoregulation of cellular morphology in F. diplosiphon.
我们对 Fremyella diplosiphon 的 TonB 蛋白（FdTonB）进行了特征描述，并研究了其在互补色适应过程中的功能。FdTonB（571 aa）的序列相似性分析导致了几个特征 TonB 蛋白的保守结构域的鉴定，包括 N 端跨膜结构域、富含脯氨酸的中央间隔区和 C 端 TonB 相关结构域（TBRD）。我们还鉴定了一个含有（Gly-X）（n）重复序列的新型甘氨酸丰富结构域。为了评估 FdTonB 的功能，我们通过基于中央富含脯氨酸间隔区、甘氨酸丰富结构域和 TBRD 截断的同源重组构建了 DeltatonB 突变体。与亲本野生型（WT）菌株相比，我们的 DeltatonB 突变体在绿光下表现出异常的细胞形态，细胞宽度扩大。WT tonB 表达使 DeltatonB 突变体的细胞形态恢复正常。有趣的是，发现 tonB 表达独立于 RcaE。由于 DeltatonB 和 WT 菌株在铁充足和铁限制条件下生长时表现出相同的反应，我们的结果表明，FdTonB 不参与 TonB 介导细胞对铁限制适应的经典功能，而是表现出与 Fremyella diplosiphon 细胞形态的光调控相关的新功能。
