Role of the S layer in morphogenesis and cell division of the archaebacterium Methanocorpusculum sinense

Abstract

Thin sections, freeze-etched, and negatively stained preparations of Methanocorpusculum sinense cells reveal a highly lobed cell structure with a hexagonally arranged surface layer (S layer). Digital image processing of negatively stained envelope fragments show that the S layer forms a porous but strongly interconnected network. Since the S layer is the exclusive cell envelope component outside the cytoplasmic membrane it must have a cell shape determining and maintaining function. Although lattice faults such as disclinations and dislocations are a geometrical necessity on the surface of a closed protein crystal, our data indicate that they also play important roles as sites for the incorporation of new morphological units, in the formation of the lobed cell structure, and in the cell division process. In freeze-etched preparations of intact cells numerous positive and negative 600 wedge disclinations can be detected which form pentagons and heptagons in the hexagonal array. Complementary pairs of pentagons and heptagons are the termination points of edge dislocations. They can be expected to function both as sites for incorporation of new morphological units into the lattice and as initiation points for the cell division process. The latter is determined by the ratio between the increase of protoplast volume and the increase in actual S-layer surface area during cell growth. We postulate that this mode of cell fission represents a common feature in lobed archaebacteria which possess an S layer as the exclusive wall component. Two-dimensional crystalline surface layers, termed S layers (36), have been observed as the outermost cell envelope component in many strains of walled eubacteria and represent an almost universal feature of archaebacterial cell envelopes (for recent compilations, see references 24, 33, and 36). Most of the presently known S layers are composed of a single protein (in some cases, a glycoprotein) species with molecular weights ranging from 40,000 to 200,000. S layers cover the bacterial cell completely and are organized in the form of crystalline lattices exhibiting oblique (p2), trigonal (p3), square (p4), or hexagonal (p6) symmetry. Isolated S-layer subunits have shown the inherent ability to self-assemble into two-dimensional arrays, either in the presence or absence of surfaces suitable for adhesion (for reviews, see references 31 and 35). These self-assembly studies have shown that all the information required for generating the two-dimensional crystalline arrays is entirely contained in the individual protomeric units (30). Considering S layers as porous crystalline arrays covering the cell surface completely, they have the potential to function as (i) protective coats, molecular sieves, and molecule and ion traps, (ii) structures involved in cell adhesion and surface recognition, and (iii) frameworks which determine and maintain cell shape (for reviews see references 1, 2, 21, 24, 34, and 37).The present study deals with the dynamic process of assembly of the S layer of the archaeb...

Analysis of the Intact Surface Layer of Caulobacter crescentus by Cryo-Electron Tomography

“…Moreover, the fact that hexagonal structures were not observed in the entire surface, even though RsaA covers the entire cell surface, reinforces the idea of a dynamic process to create new S layer (40). Figure 2 shows several ridges on the S-layer surface where different growth areas may have merged.…”

Surface-Layer (S-Layer) Proteins Sap and EA1 Govern the Binding of the S-Layer-Associated Protein BslO at the Cell Septa of Bacillus anthracis

“…Perfect S-layer networks that assemble into closed crystal structures are thought to expand by the incorporation of additional monomers at gliding dislocations in a process termed "intussusception" (26). However, the spectrum of SLH domain proteins predicted to occupy the cell surface alone implies that this heterogeneity prevents the formation of closed crystalline structures.…”

S-Layer Proteins

“…Analysis of the lattice faults in S-layers of lobed archaea possessing hexagonal arrays as the exclusive wall component provided strong evidence that complementary pairs of pentagons and heptagons play an important role as sites for the incorporation of new subunits in the formation and maintenance of the cell structure and in the fission process. The latter was assumed to be dependent on the ratio of the increase in protoplast volume to the increase in actual S-layer surface area during cell growth (106).…”