Bactofilins are rigid, nonpolar bacterial cytoskeletal filaments that link cellular processes to specific curvatures of the cytoplasmic membrane. Although homologs of bactofilins have been identified in archaea and eukaryotes, functional studies have remained confined to bacterial systems. Here, we characterize representatives of two families of archaeal bactofilins from the pleomorphic archaeon Haloferax volcanii , halofilin A (HalA) and halofilin B (HalB). HalA and HalB polymerize in vitro, assembling into straight bundles. HalA polymers are highly dynamic and accumulate at positive membrane curvatures in vivo, whereas HalB forms more static foci that localize in areas of local negative curvatures on the outer cell surface. Gene deletions and live-cell imaging show that halofilins are critical in maintaining morphological integrity during shape transition from disk (sessile) to rod (motile). Morphological defects in Δ halA result in accumulation of highly positive curvatures in rods but not in disks. Conversely, disk-shaped cells are exclusively affected by halB deletion, resulting in flatter cells. Furthermore, while Δ halA and Δ halB cells imprecisely determine the future division plane, defects arise predominantly during the disk-to-rod shape remodeling. The deletion of halA in the haloarchaeon Halobacterium salinarum , whose cells are consistently rod-shaped, impacted morphogenesis but not cell division. Increased levels of halofilins enforced drastic deformations in cells devoid of the S-layer, suggesting that HalB polymers are more stable at defective S-layer lattice regions. Our results suggest that halofilins might play a significant mechanical scaffolding role in addition to possibly directing envelope synthesis.

中文翻译：

---

Halofilins 作为古细菌细胞形状可塑性协调器的新兴细菌素家族


Bactofilins 是刚性的、非极性的细菌细胞骨架丝，将细胞过程与细胞质膜的特定曲率连接起来。尽管已在古细菌和真核生物中鉴定出细菌素的同系物，但功能研究仍仅限于细菌系统。在这里，我们描述了来自多形古菌 Haloferax volcanii 的两个古细菌 bactofilin 家族的代表，halofilin A (HalA) 和 halofilin B (HalB)。 HalA 和 HalB 在体外聚合，组装成直束。 HalA 聚合物具有高度动态性，并在体内以正膜曲率积累，而 HalB 则形成更多静态焦点，定位于细胞外表面局部负曲率区域。基因删除和活细胞成像表明，halofilins 在形状从盘（无柄）到杆（活动）转变过程中对于维持形态完整性至关重要。 Δ halA 的形态缺陷导致杆中高度正曲率的积累，但盘中却没有。相反，盘形细胞仅受 halB 缺失的影响，从而产生更扁平的细胞。此外，虽然 Δ halA 和 Δ halB 细胞不精确地确定未来的分割平面，但缺陷主要出现在盘状到棒状的形状重塑过程中。盐古菌盐杆菌（其细胞始终呈杆状）中 halA 的缺失影响形态发生，但不影响细胞分裂。 halofilins 水平的增加会导致缺乏 S 层的细胞发生剧烈变形，这表明 HalB 聚合物在有缺陷的 S 层晶格区域更加稳定。我们的结果表明，halofilins 除了可能指导包膜合成外，还可能发挥重要的机械支架作用。