Structure of the two-component S-layer of the archaeon Sulfolobus acidocaldarius

Abstract

Surface layers (S-layers) are resilient two-dimensional protein lattices that encapsulate many bacteria and most archaea. In archaea, S-layers usually form the only structural component of the cell wall and thus act as the final frontier between the cell and its environment. Therefore, S-layers are crucial for supporting microbial life. Notwithstanding their importance, little is known about archaeal S-layers at the atomic level. Here, we combined single particle cryo electron microscopy (cryoEM), cryo electron tomography (cryoET) and Alphafold2 predictions to generate an atomic model of the two-component S-layer of Sulfolobus acidocaldarius. The outer component of this S-layer (SlaA) is a flexible, highly glycosylated, and stable protein. Together with the inner and membrane-bound component (SlaB), they assemble into a porous and interwoven lattice. We hypothesise that jackknife-like conformational changes, changes play important roles in S-layer assembly.

Membraneless channels sieve cations in ammonia-oxidizing marine archaea

“…The N. maritimus genome also encodes a homologue for a cell-anchoring SlaB protein (Extended Data Fig. 5a,b and Supplementary Table 1 ) that is known to bind the S-layer of the archaeon Sulfolobus acidocaldarius to the cell membrane 24 . However, proteomic data on N. maritimus indicate that this protein is considerably less abundant in the cell than Nm SLP 15 .…”

“…Although these SLPs share some structural similarities, they diverge notably at the sequence level, as well as at the overall organizational level containing different number of domains (Extended Data Fig. 5c ), enabling them to assemble into unique two-dimensional sheets 23 , 24 , each with distinctly different glycosylation patterns and cell anchoring mechanisms.…”

Exploring surface structures

“…However, there is much about two-component surface layers that we do not fully understand. Now, in eLife, Bertram Daum from the University of Exeter and co-workers – including Lavinia Gambelli as first author – report details of an in situ atomic model of a two-component surface layer that sheds new light on the dynamics and assembly of these structures ( Gambelli et al, 2024 ). The study was performed with samples from Sulfolobus acidocaldarius , an archaeal species that lives in hot springs, and relied on a combination of experimental techniques – notably cryo electron microscopy and cryo electron tomography – and a software package called Alphafold2 that predicts protein structures.…”