What is S layer Protein in Bacteria?

What are S layers (Surface layer) in bacterial cell envelope?
S-layer (surface layer proteins) is a regularly structured crystalline layer present on the surface of many bacteria and archaebacteria.

Chemical nature:
The S-layer is composed of protein or glycoprotein.

S layer glycoprotein

Location: In Gram positive bacteria, S-layer is associated with peptidoglycan surface.
In Gram negative bacteria, it is associated with the outer membrane (lipopolysaccharide layer)

In archaebacteria, S layer proteins are arranged in different ways in the cell envelope.

Biological Functions:
  • Protecting cell against ion and pH fluctuations, osmotic stress, degrading enzymes or predacious bacteria.
  • Helps in maintaining shape and envelope rigidity of the cell
  • It promote cell adhesion to surfaces
  • It contributes to the virulence of bacteria.
  • Widely studied recently especially in connection with nanotechnology due to their ability to self assemble protein units without the aid of enzymes.
Future prospects: S-layer could be used technologies such as drug delivery systems and novel detection systems for toxic chemicals.

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