Major facilitator superfamily

The major facilitator superfamily ( MFS) is a family of membrane proteins. The members of this family form the largest group of transporters. Transporting dissolved compounds across cell membranes and are present in all organisms. Transport mode can be both secondary active and passive ( facilitated diffusion ).

Design and function

The MF superfamily consists of 58 individual families with previously sequenced approximately 5000 different proteins. This number will continue to grow as part of the ongoing sequencing of organisms. The major facilitator superfamily is ubiquitous - in all organisms and all its biological cells. They work as a uniporter (transport of only one substrate ) symporter (transport of two or more substrates ) or as an antiporter (transport in the opposite direction).

The MFS antiporter - probably even all MFS proteins - have the same three-dimensional structure. They consist of two domains that surround a substrate translocation. In contrast to ABC transporters they have no ATP - binding domains and in contrast to ion channels do not form a continuous connection between the two sides of a membrane. They consist of 400 to 600 amino acids.

A typical MFS transporter is divided into its amino acid sequence in a total of 11 to 12 sections, which are composed primarily of hydrophobic amino acid and are located in the cell membrane. Because the α -helical secondary structure of this region are also referred to as transmembrane helices ( TMH ). The transmembrane helices are connected to one another usually with hydrophilic amino acids that both intra - and extracellularly located.

The transport takes place through a conformational change of the transporter protein. The substrate binding site extends into either the intra-or the extracellular space. A substrate extracellularly bound, the MFS transporters changes its conformation, so that the substrate is transported into the cytoplasm. Then again removes the link between transporter and substrate, the transporter takes its starting conformation again and can thus record the next substrate. The individual steps of the transport cycle balance with each other.

In evolutionary terms, it is a relatively old gene family that encodes the major facilitator superfamily. The corresponding genes are found in bacteria, archaea, animals, plants and fungi occur. For example, there is a close relationship between the glucose transporters of bacteria and mammals. The amino acid sequences are highly conserved.

An important subfamily of the major facilitator superfamily, is the family of solute carrier (SLC ).

Examples of MFS transporters

• GLUT -1 is a glucose transporter, which is encoded by the SLC2A1 gene.
• Glucose- 6-phosphate translocase transports glucose -6-phosphatase in the cytoplasm ( a antiporter ) and SLC37A4 gene encodes