Fungal Cell Envelope

The fungal cell envelope is the layered boundary surrounding the cytoplasm. In most fungi, it consists principally of an inner plasma membrane and an external, mechanically strong cell wall; some fungi also produce an outer capsule or extracellular matrix.

Cell wall framework

The fungal cell wall is a dynamic, porous structure that maintains shape, resists osmotic pressure and supports interactions with the environment.

• Chitin consists of chains of N-acetylglucosamine and forms strong microfibrils that reinforce the wall.
• Beta-glucans, especially beta-1,3-glucans associated with beta-1,6 linkages, provide the main polysaccharide framework in many fungi.
• Mannoproteins and other glycoproteins are concentrated toward the outer wall and contribute to adhesion, wall porosity and surface properties.
• The proportions and arrangement of chitin, glucans and glycoproteins vary among fungal groups and between growth forms.

Plasma membrane

Beneath the wall lies a phospholipid bilayer containing proteins and the characteristic fungal sterol ergosterol. The membrane controls transport, signalling and synthesis of several cell-wall components; ergosterol also helps regulate membrane stability and fluidity.

Additional external layers

Some fungi possess an external polysaccharide capsule, mucilaginous layer or extracellular matrix. These structures are not universal components of the fungal envelope, but where present they can promote adhesion, retain water and protect the cell from environmental or host defences.