S-layer

S-layer is a part of the cell envelope found in almost all archaea, as well as in many types of bacteria. The S-layer is directly attached to the outermost part of the cell, and it provides a rigid but flexible covering over the entire cell surface. This layer is composed of a single type of protein or glycoprotein that self-assembles into a two-dimensional crystalline lattice.

Structure

The S-layer is typically 5-25 nm thick, with a pore size of 2-8 nm. The individual proteins or glycoproteins are typically 40-200 kDa in size, and they form a lattice with a unit cell of 3-30 nm. The lattice can be oblique (p1, p2), square (p4), or hexagonal (p3, p6) in symmetry.

Function

The S-layer provides a protective coat to the cell and can act as a barrier against large molecules and ions. It also plays a role in cell adhesion and surface recognition. In some bacteria, the S-layer is involved in pathogenicity.

S-layer in Archaea

In archaea, the S-layer is the only component of the cell wall and it is composed of proteins or glycoproteins. The S-layer in archaea is attached to the plasma membrane via lipid anchors.

S-layer in Bacteria

In bacteria, the S-layer is attached to the peptidoglycan layer by secondary cell wall polymers. In some bacteria, the S-layer is associated with the outer membrane.

See also

• Cell wall
• Archaea
• Bacteria
• Protein
• Glycoprotein

References

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