Structure of Geobacter OmcZ filaments suggests extracellular cytochrome polymers evolved independently multiple times.
Structure of Geobacter OmcZ filaments suggests extracellular cytochrome polymers evolved independently multiple times.
复制标题
DOI：
10.7554/elife.81551
复制
发表时间：
2022-09-05
期刊：
影响因子：
7.7
通讯作者：
Bond, Daniel R.
中科院分区：
文献类型：
--
作者：
Wang, Fengbin;Chan, Chi Ho;Suciu, Victor;Mustafa, Khawla;Ammend, Madeline;Si, Dong;Hochbaum, Allon, I;Egelman, Edward H.;Bond, Daniel R.
虽然早期的遗传学和低分辨率结构观察表明，金属还原生物(如地质杆菌)上的胞外传导细丝由IV型菌毛组成，但现在已经证实，细菌的c型细胞色素可以聚合形成能够远程电子传输的胞外细丝。存在两种这样的细胞色素细丝的原子结构，它们是由六铁血红素细胞色素OMCs和四铁血红素细胞色素OMCs形成的。由于中心OMCs和OMCE核心中高度保守的血红素堆积，以及亚单位之间共同的血红素配位模式，人们认为这些聚合物具有共同的起源。我们现在已经使用冷冻电子显微镜(CRYO-EM)来确定第三个胞外细丝的结构，该细丝由硫磺还原地质杆菌八种血红素细胞色素OmcZ形成。与同一生物体的OMCs和OMCE中的线性血红素链相比，OMCZ中的血红素的堆积、血红素：血红素的角度和亚基间的血红素配位有很大的不同。OmcZ内的分支血红素排列导致每个亚基中都有高度表面暴露的血红素，这可能是形成导电生物膜网络的原因，并解释了OmcZ细丝测量到的较高电导率。这一新的结构证据表明，导电细胞色素聚合物不止一次独立地出现在不同的祖先多血红素蛋白中。
While early genetic and low-resolution structural observations suggested that extracellular conductive filaments on metal-reducing organisms such as Geobacter were composed of type IV pili, it has now been established that bacterial c-type cytochromes can polymerize to form extracellular filaments capable of long-range electron transport. Atomic structures exist for two such cytochrome filaments, formed from the hexaheme cytochrome OmcS and the tetraheme cytochrome OmcE. Due to the highly conserved heme packing within the central OmcS and OmcE cores, and shared pattern of heme coordination between subunits, it has been suggested that these polymers have a common origin. We have now used cryo-electron microscopy (cryo-EM) to determine the structure of a third extracellular filament, formed from the Geobacter sulfurreducens octaheme cytochrome, OmcZ. In contrast to the linear heme chains in OmcS and OmcE from the same organism, the packing of hemes, heme:heme angles, and between-subunit heme coordination is quite different in OmcZ. A branched heme arrangement within OmcZ leads to a highly surface exposed heme in every subunit, which may account for the formation of conductive biofilm networks, and explain the higher measured conductivity of OmcZ filaments. This new structural evidence suggests that conductive cytochrome polymers arose independently on more than one occasion from different ancestral multiheme proteins.