Protein subunit explained

In structural biology, a protein subunit is a polypeptide chain or single protein molecule that assembles (or "coassembles") with others to form a protein complex.[1] [2] [3] Large assemblies of proteins such as viruses often use a small number of types of protein subunits as building blocks.[4]

A subunit is often named with a Greek or Roman letter, and the numbers of this type of subunit in a protein is indicated by a subscript.[5] For example, ATP synthase has a type of subunit called α. Three of these are present in the ATP synthase molecule, leading to the designation α3. Larger groups of subunits can also be specified, like α3β3-hexamer and c-ring.[6]

Naturally occurring proteins that have a relatively small number of subunits are referred to as oligomeric.[7] For example, hemoglobin is a symmetrical arrangement of two identical α-globin subunits and two identical β-globin subunits.[3] [8] Longer multimeric proteins such as microtubules and other cytoskeleton proteins may consist of very large numbers of subunits. For example, dynein is a multimeric protein complex involving two heavy chains (DHCs), two intermediate chains (ICs), two light-intermediate chains (LICs) and several light chains (LCs).[9]

The subunits of a protein complex may be identical, homologous or totally dissimilar and dedicated to disparate tasks.[1] In some protein assemblies, one subunit may be a "catalytic subunit" that enzymatically catalyzes a reaction, whereas a "regulatory subunit" will facilitate or inhibit the activity.[10] Although telomerase has telomerase reverse transcriptase as a catalytic subunit, regulation is accomplished by factors outside the protein.[11]

An enzyme composed of both regulatory and catalytic subunits when assembled is often referred to as a holoenzyme. For example, class I phosphoinositide 3-kinase is composed of a p110 catalytic subunit and a p85 regulatory subunit.[12] One subunit is made of one polypeptide chain. A polypeptide chain has one gene coding for it – meaning that a protein must have one gene for each unique subunit.

See also

Notes and References

  1. Book: Stoker . H. Stephen . General, Organic, and Biological Chemistry . 1 January 2015 . Cengage Learning . Boston, MA . 978-1-305-68618-2 . 709–710 . 7th . 15 April 2022 . en.
  2. Book: Smith . Michael B. . Biochemistry: An Organic Chemistry Approach . 27 April 2020 . CRC Press . Boca Raton . 978-1-351-25807-4 . 269–270 . 15 April 2022 . en.
  3. Book: Alberts . Bruce . Johnson . Alexander . Lewis . Julian . Raff . Martin . Roberts . Keith . Walter . Peter . The Shape and Structure of Proteins . 2002 . Garland Science . New York . 15 April 2022 . en.
  4. Book: Vijayan . M. . Yathindra . N. . Kolaskar . A. S. . Kumar . A. . Evarsson . A. . Hol . W. G. J. . Perspectives in Structural Biology: A Volume in Honour of G.N. Ramachandran . Multi-protein assemblies with point group symmetry . 1999 . Universities Press . Hyderabad, India . 978-81-7371-254-8 . 449–466 . https://books.google.com/books?id=xTy_M3B5sf4C&pg=PA462 . 15 April 2022 . en.
  5. Book: Lesieur . Claire . Oligomerization of Chemical and Biological Compounds . 18 June 2014 . Intech . Croatia . 978-953-51-1617-2 . 240–241 . 15 April 2022 . en.
  6. Ahmad . Zulfiqar . Okafor . Florence . Azim . Sofiya . Laughlin . Thomas F. . ATP Synthase: A Molecular Therapeutic Drug Target for Antimicrobial and Antitumor Peptides . Current Medicinal Chemistry . 2013 . 20 . 15 . 1956–1973 . 10.2174/0929867311320150003 . 23432591 . 4734648 . 0929-8673.
  7. Glossary of basic terms in polymer science (IUPAC Recommendations 1996). Pure and Applied Chemistry. 1996. 68. 12. 2287–2311. 10.1351/pac199668122287. Jenkins. A. D.. Kratochvíl. P.. Stepto. R. F. T.. Suter. U. W.. free. Quote: Oligomer molecule: A molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass.
  8. Book: Liu . Shijie . Bioprocess Engineering: Kinetics, Sustainability, and Reactor Design . 7 April 2020 . Elsevier . 978-0-12-822383-3 . 358 . 15 April 2022 . en.
  9. Dharan . Adarsh . Campbell . Edward M. . Role of Microtubules and Microtubule-Associated Proteins in HIV-1 Infection . Journal of Virology . 31 July 2018 . 92 . 16 . e00085–18 . 10.1128/JVI.00085-18 . 29899089 . 6069196 . 0022-538X.
  10. Søberg . Kristoffer . Skålhegg . Bjørn Steen . The Molecular Basis for Specificity at the Level of the Protein Kinase a Catalytic Subunit . Frontiers in Endocrinology . 12 September 2018 . 9 . 538 . 10.3389/fendo.2018.00538 . 30258407 . 6143667 . 1664-2392. free .
  11. Daniel M, Peek GW, Tollefsbol TO . Regulation of the human catalytic subunit of telomerase (hTERT) . . 498 . 2 . 2012 . 135–46 . 10.1016/j.gene.2012.01.095 . 3312932 . 22381618.
  12. Carpenter CL, Duckworth BC, Auger KR, Cohen B, Schaffhausen BS, Cantley LC . Purification and characterization of phosphoinositide 3-kinase from rat liver . J. Biol. Chem. . 265 . 32 . 19704–11 . November 1990 . 10.1016/S0021-9258(17)45429-9 . 2174051 . free .

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