“Bitopic protein”的意思、由来-开放百科全书

词条

Bitopic protein

释义

Topology-based classification
Databases
References

Bitopic proteins (also known as single-pass or single-spanning proteins) are transmembrane proteins that span the lipid bilayer only one time.^[1] These proteins may constitute up to 50% of all transmembrane proteins, depending on the organism, and contribute significantly to the network of interactions between different proteins in cells, including interactions via transmembrane helices.^[2] They usually include one or several water-soluble domains situated at the different sides of biological membranes, for example in single-pass transmembrane receptors. Some of them are small and serve as regulatory or structure-stabilizing subunits in large multi-protein transmembrane complexes, such as photosystems or the respiratory chain.

Topology-based classification

Bitopic proteins are classified into 4 types, depending on their transmembrane topology and location of the transmembrane helix in the amino acid sequence of the protein. According to Uniprot^[3]:

Type I is bitopic protein with its N-terminus on the extracellular side of the membrane and removed signal peptide;
Type II is bitopic protein with its N-terminus on the cytoplasmic side of the membrane and the transmembrane helix located close to the N-terminus, where it works as an anchor;
Type III is bitopic protein with its N-terminus on the extracellular side of the membrane and no signal peptide;
Type IV is bitopic protein with its N-terminus on the cytoplasmic side of the membrane, and the transmembrane helix located close to the C-terminus, where it works as an anchor.

Hence type I proteins are anchored to the lipid membrane with a stop-transfer anchor sequence and have their N-terminal domains targeted to the ER lumen during synthesis (and the extracellular space, if mature forms are located on plasmalemma). Type II and III are anchored with a signal-anchor sequence, with type II being targeted to the ER lumen with its C-terminal domain, while type III have their N-terminal domains targeted to the ER lumen. Type IV is subdivided into IV-A, with their N-terminal domains targeted to the cytosol and IV-B, with an N-terminal domain targeted to the lumen.^[4] The implications for the division in the four types are especially manifest at the time of translocation and ER-bound translation, when the protein has to be passed through the ER membrane in a direction dependent on the type.

Databases

Membranome database is a database of bitopic proteins from several model organisms.
Bitopic proteins in OPM database

References

1. ^Membrane Structural Biology: With Biochemical and Biophysical Foundations, by Mary Luckey, 2014, Cambridge University Press, page 91.
2. ^{{cite journal|title=How important are transmembrane helices of bitopic membrane proteins?|first1=Moti|last1=Zviling|first2=Uzi|last2=Kochva|first3=Isaiah T.|last3=Arkin|journal=Biochimica et Biophysica Acta (BBA) - Biomembranes|volume=1768|issue=3|doi=10.1016/j.bbamem.2006.11.019}}
3. ^Topology definitions in Uniprot, see [https://www.uniprot.org/locations/SL-9905],[https://www.uniprot.org/locations/SL-9908]
4. ^Harvey Lodish etc.; Molecular Cell Biology, Sixth edition, p.546

1 : Single-pass transmembrane proteins

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