Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Organismic Interactions, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
Proteome Center Tübingen, University of Tübingen, Auf der Morgenstelle 15, 72076 Tübingen, Germany.
Mol Microbiol. 2018 Apr;108(2):187-203. doi: 10.1111/mmi.13929. Epub 2018 Mar 2.
Heterocyst-forming cyanobacteria are organized as multicellular filaments of tightly interacting, functionally specialized cells. N -fixing heterocysts differentiate from vegetative cells under nitrogen limitation in a semi-regular pattern along the filament. Diazotrophic growth requires metabolite exchange between neighboring cells within the filament. This exchange occurs via cell-cell junction complexes that span the gap between the plasma membranes and thereby cross the septal peptidoglycan through an array of uniform nanopores formed by AmiC-type cell wall hydrolases. We investigated how the lytic hydrolase AmiC1 (Alr0092) from Anabaena sp. PCC 7120, whose activity needs to be tightly controlled to avoid cell lysis, is regulated by the LytM factor Alr3353. Inactivation of alr3353 resulted in significantly fewer nanopores and as a consequence, a lower rate of fluorescent tracer exchange between cells. The mutant was not able to grow with N as sole nitrogen source, although heterocysts were formed. Alr3353 localized mainly to fully developed intercellular septa of vegetative cells. The purified protein bound to peptidoglycan and enhanced the hydrolytic activity of AmiC1 in vitro. Our data show that the LytM factor Alr3353 regulates nanopore formation and cell-cell communication by directly interacting with AmiC1.
异形胞形成的蓝藻以紧密相互作用、功能专业化的细胞组成多细胞丝。在氮限制下，固氮异形胞从营养细胞中以半规则的模式沿着丝状体分化。固氮生长需要丝状体中相邻细胞之间的代谢物交换。这种交换通过跨越质膜间隙的细胞-细胞连接复合物发生，从而穿过由 AmiC 型细胞壁水解酶形成的一系列均匀纳米孔的隔膜肽聚糖。我们研究了来自 Anabaena sp. PCC 7120 的裂解水解酶 AmiC1（Alr0092）如何受到 LytM 因子 Alr3353 的调节，其活性需要严格控制以避免细胞裂解。Alr3353 的失活导致纳米孔明显减少，因此细胞之间荧光示踪剂交换的速度降低。尽管形成了异形胞，但突变体不能以 N 作为唯一氮源生长。Alr3353 主要定位于营养细胞完全发育的细胞间隔膜上。纯化的蛋白质与肽聚糖结合，并在体外增强了 AmiC1 的水解活性。我们的数据表明，LytM 因子 Alr3353 通过直接与 AmiC1 相互作用来调节纳米孔形成和细胞间通讯。
