S-layer Totally Explained

Everything about S-layer totally explained

An S-layer (surface layer) is a part of the cell envelope commonly found in bacteria, as well as among archaea. It consists of a monomolecular layer composed of identical proteins or glycoproteins. This two dimensional structure is built via self-assembly and encloses the whole cell surface. Thus, the S-layer protein can represent up to 10-15% of the whole protein content of a cell
. S-layer proteins are poorly or not conserved at all and can differ markedly even between related species. Depending on species the S-layers have a thickness between 5 and 25 nm and possess identical pores with 2-8 nm in diameter . S-layers exhibit either an oblique (p1, p2), square (p4) or hexagonal (p3, p6) lattice symmetry. Depending on the lattice symmetry the S-layer is composed of one (P1), two (P2), three (P3), four (P4) or six (P6) identical protein subunits, respectively. The centre to centre spacings (or unit cell dimensions) between these subunits range between 2.5 and 35 nm.

Fixation of S-layers in the cell wall

In Gram-negative bacteria S-layers are associated to the LPS via ionic, carbohydrate-carbohydrate, protein carbohydrate interactions and/or protein-protein interactions.
In Gram-positive bacteria whose S-layers contain surface layer homology (SLH) domains the binding occurs to the peptidoglycan and to a secondary cell wall polymer (for example teichuronic acids). In the absence of SLH domains the binding occurs via electrostatic interactions between the positively charged N-terminus of the S-layer protein and a negatively charged secondary cell wall polymer.
In Gram-negative archaea S-layer proteins possess a hydrophobic anchor that's associated with the underlying lipid membrane.
In Gram-positive archaea the S-layer proteins bind pseudomurein or to methanochondritin.

Biological functions of the S-layer

As for many bacteria the S-layer represents the outermost interaction zone with their respective environment, its functions are very diverse and vary from species to species. In Gram-negative archaea the S-layer is the only cell wall component and therefore is important for mechanical stabilisation. Additional functions associated with S-layers include:

protection against bacteriophages and phagocytosis

resistance against low pH

barrier against high molecular weight substances (for example lytic enzymes)

adhesion (for glycosylated S-layers)

stabilisation of the membrane

provide adhesion sites for exoproteins

provide a periplasmic compartment in Gram-positive prokaryotes together with the peptidoglycan and the cytoplasmic membrane

Further Information

Get more info on 'S-layer'.

External Link Exchanges

Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:

<a href="http://s-layer.totallyexplained.com">S-layer Totally Explained</a>

Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned.