The archaeal protein SepF is essential for cell division in Haloferax volcanii

Abstract

In most bacteria, cell division depends on the tubulin homolog FtsZ and other proteins, such as SepF, that form a complex termed the divisome. Cell division also depends on FtsZ in many archaea, but other components of the divisome are unknown. Here, we demonstrate that a SepF homolog plays important roles in cell division in Haloferax volcanii, a halophilic archaeon that is known to have two FtsZ homologs with slightly different functions (FtsZ1 and FtsZ2). SepF co-localizes with both FtsZ1 and FtsZ2 at midcell. Attempts to generate a sepF deletion mutant were unsuccessful, suggesting an essential role. Indeed, SepF depletion leads to severe cell division defects and formation of large cells. Overexpression of FtsZ1-GFP or FtsZ2-GFP in SepF-depleted cells results in formation of filamentous cells with a high number of FtsZ1 rings, while the number of FtsZ2 rings is not affected. Pull-down assays support that SepF interacts with FtsZ2 but not with FtsZ1, although SepF appears delocalized in the absence of FtsZ1. Archaeal SepF homologs lack a glycine residue known to be important for polymerization and function in bacteria, and purified H. volcanii SepF forms dimers, suggesting that polymerization might not be important for the function of archaeal SepF.

Targeting the Achilles Heel of FtsZ: The Interdomain Cleft

“…The Z–ring is anchored to the membrane with the help of other essential cell division proteins, such as FtsA and ZipA of E. coli ( Pichoff and Lutkenhaus, 2002 ). In Gram positive bacteria as well as FtsZ-containing archaea, SepF is the key membrane anchor for FtsZ ( Duman et al, 2013 ; Nussbaum et al, 2021 ; White and Eswara, 2021 ).…”

The cell biology of archaea

“…Recent data has added further information on the FtsZ-based cell division machinery in archaea by showing for the first time that a homologue of SepF anchors the Z-ring to the membrane, as it does in many bacteria 102 , 103 ( Figure 4F ). Interestingly, however, the structure of SepF in complex with FtsZ show striking differences from its bacterial counterpart; this may reflect the early evolutionary divergence of the cell envelopes in the two prokaryotic domains and/or differences in SepF/FtsZ function required to deform such very different types of cell walls 102 , 103 . Curiously, and differently from bacteria, none of the MinD homologues identified in H. volcanii are involved in localizing FtsZ at midcell 104 .…”

Structural Insights into the Interaction between Bacillus subtilis SepF Assembly and FtsZ by Solid-State NMR Spectroscopy

“…The function of SepF in cell division was first discovered in Streptococcus pneumonia , that the depletion of SepF leads to highly deformed septa . Similarly, the depletion of SepF in Haloferax volcanii or Mycobacterium tuberculosis results in the formation of large cells or defective growth. Further studies indicated an additional function of SepF in Bacillus subtilis to shape the cell wall due to its intrinsic property of forming ring structures .…”

“…SepF is located at the Z-ring forming area and has a direct interaction with FtsZ during division. It interacts with the C-terminus of FtsZ like many other regulating proteins and is a candidate for FtsZ membrane tethering. − In SepF-deleted cells, FtsZ failed to localize to the site of division. , Meanwhile, copolymerization of FtsZ and SepF in vitro lead to a promotion of the assembly and protofilament bundling of FtsZ . The action mode between SepF and FtsZ has been suggested by crystal structures obtained from bacteria Corynebacterium glutamicum and archaea Methanobrevibacter smithii .…”