Protein subunit

Last updated
Rendering of HLA-A11 showing the a (A*1101 gene product) and b (Beta-2 microglobulin) subunits. This receptor has a bound peptide (in the binding pocket) of heterologous origin that also contributes to function. HLA-A11.png
Rendering of HLA-A11 showing the α (A*1101 gene product) and β (Beta-2 microglobulin) subunits. This receptor has a bound peptide (in the binding pocket) of heterologous origin that also contributes to function.

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

Related Research Articles

<span class="mw-page-title-main">Proteasome</span> Protein complexes which degrade unnecessary or damaged proteins by proteolysis

Proteasomes are protein complexes which degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases.

A protein phosphatase is a phosphatase enzyme that removes a phosphate group from the phosphorylated amino acid residue of its substrate protein. Protein phosphorylation is one of the most common forms of reversible protein posttranslational modification (PTM), with up to 30% of all proteins being phosphorylated at any given time. Protein kinases (PKs) are the effectors of phosphorylation and catalyse the transfer of a γ-phosphate from ATP to specific amino acids on proteins. Several hundred PKs exist in mammals and are classified into distinct super-families. Proteins are phosphorylated predominantly on Ser, Thr and Tyr residues, which account for 79.3, 16.9 and 3.8% respectively of the phosphoproteome, at least in mammals. In contrast, protein phosphatases (PPs) are the primary effectors of dephosphorylation and can be grouped into three main classes based on sequence, structure and catalytic function. The largest class of PPs is the phosphoprotein phosphatase (PPP) family comprising PP1, PP2A, PP2B, PP4, PP5, PP6 and PP7, and the protein phosphatase Mg2+- or Mn2+-dependent (PPM) family, composed primarily of PP2C. The protein Tyr phosphatase (PTP) super-family forms the second group, and the aspartate-based protein phosphatases the third. The protein pseudophosphatases form part of the larger phosphatase family, and in most cases are thought to be catalytically inert, instead functioning as phosphate-binding proteins, integrators of signalling or subcellular traps. Examples of membrane-spanning protein phosphatases containing both active (phosphatase) and inactive (pseudophosphatase) domains linked in tandem are known, conceptually similar to the kinase and pseudokinase domain polypeptide structure of the JAK pseudokinases. A complete comparative analysis of human phosphatases and pseudophosphatases has been completed by Manning and colleagues, forming a companion piece to the ground-breaking analysis of the human kinome, which encodes the complete set of ~536 human protein kinases.

<span class="mw-page-title-main">Protein quaternary structure</span> Number and arrangement of multiple folded protein subunits in a multi-subunit complex

Protein quaternary structure is the fourth classification level of protein structure. Protein quaternary structure refers to the structure of proteins which are themselves composed of two or more smaller protein chains. Protein quaternary structure describes the number and arrangement of multiple folded protein subunits in a multi-subunit complex. It includes organizations from simple dimers to large homooligomers and complexes with defined or variable numbers of subunits. In contrast to the first three levels of protein structure, not all proteins will have a quaternary structure since some proteins function as single units. Protein quaternary structure can also refer to biomolecular complexes of proteins with nucleic acids and other cofactors.

<span class="mw-page-title-main">Kinase</span> Enzyme catalyzing transfer of phosphate groups onto specific substrates

In biochemistry, a kinase is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule donates a phosphate group to the substrate molecule. This transesterification produces a phosphorylated substrate and ADP. Conversely, it is referred to as dephosphorylation when the phosphorylated substrate donates a phosphate group and ADP gains a phosphate group. These two processes, phosphorylation and dephosphorylation, occur four times during glycolysis.

<span class="mw-page-title-main">ATP synthase</span> Enzyme

ATP synthase is an enzyme that catalyzes the formation of the energy storage molecule adenosine triphosphate (ATP) using adenosine diphosphate (ADP) and inorganic phosphate (Pi). ATP synthase is a molecular machine. The overall reaction catalyzed by ATP synthase is:

<span class="mw-page-title-main">Protein kinase A</span> Family of enzymes

In cell biology, protein kinase A (PKA) is a family of serine-threonine kinase whose activity is dependent on cellular levels of cyclic AMP (cAMP). PKA is also known as cAMP-dependent protein kinase. PKA has several functions in the cell, including regulation of glycogen, sugar, and lipid metabolism. It should not be confused with 5'-AMP-activated protein kinase.

<span class="mw-page-title-main">Glycogen phosphorylase</span> Class of enzymes

Glycogen phosphorylase is one of the phosphorylase enzymes. Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphorylase is also studied as a model protein regulated by both reversible phosphorylation and allosteric effects.

<span class="mw-page-title-main">Acetyl-CoA carboxylase</span> Enzyme that regulates the metabolism of fatty acids

Acetyl-CoA carboxylase (ACC) is a biotin-dependent enzyme that catalyzes the irreversible carboxylation of acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT). ACC is a multi-subunit enzyme in most prokaryotes and in the chloroplasts of most plants and algae, whereas it is a large, multi-domain enzyme in the cytoplasm of most eukaryotes. The most important function of ACC is to provide the malonyl-CoA substrate for the biosynthesis of fatty acids. The activity of ACC can be controlled at the transcriptional level as well as by small molecule modulators and covalent modification. The human genome contains the genes for two different ACCs—ACACA and ACACB.

<span class="mw-page-title-main">Phosphoinositide 3-kinase</span> Class of enzymes

Phosphoinositide 3-kinases (PI3Ks), also called phosphatidylinositol 3-kinases, are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which in turn are involved in cancer.

<span class="mw-page-title-main">P110α</span> Human protein-coding gene

The phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha, also called p110α protein, is a class I PI 3-kinase catalytic subunit. The human p110α protein is encoded by the PIK3CA gene.

Fatty acid synthase (FAS) is an enzyme that in humans is encoded by the FASN gene.

<span class="mw-page-title-main">Carbamoyl phosphate synthetase</span> Class of enzymes

Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis of carbamoyl phosphate from glutamine or ammonia and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP. Carboxy phosphate reacts with ammonia to give carbamic acid. In turn, carbamic acid reacts with a second ATP to give carbamoyl phosphate plus ADP.

<span class="mw-page-title-main">PRKACA</span> Protein-coding gene in the species Homo sapiens

The catalytic subunit α of protein kinase A is a key regulatory enzyme that in humans is encoded by the PRKACA gene. This enzyme is responsible for phosphorylating other proteins and substrates, changing their activity. Protein kinase A catalytic subunit is a member of the AGC kinase family, and contributes to the control of cellular processes that include glucose metabolism, cell division, and contextual memory. PKA Cα is part of a larger protein complex that is responsible for controlling when and where proteins are phosphorylated. Defective regulation of PKA holoenzyme activity has been linked to the progression of cardiovascular disease, certain endocrine disorders and cancers.

<span class="mw-page-title-main">Calcium/calmodulin-dependent protein kinase type II subunit alpha</span> Protein-coding gene in the species Homo sapiens

Calcium/calmodulin-dependent protein kinase type II subunit alpha (CAMKIIα), a.k.a.Ca2+/calmodulin-dependent protein kinase II alpha, is one subunit of CamKII, a protein kinase (i.e., an enzyme which phosphorylates proteins) that in humans is encoded by the CAMK2A gene.

<span class="mw-page-title-main">PPP2CA</span> Enzyme

Serine/threonine-protein phosphatase 2A catalytic subunit alpha isoform is an enzyme that is encoded by the PPP2CA gene.

<span class="mw-page-title-main">PRKAR2A</span> Protein-coding gene in the species Homo sapiens

cAMP-dependent protein kinase type II-alpha regulatory subunit is an enzyme that in humans is encoded by the PRKAR2A gene.

<span class="mw-page-title-main">PRKAR2B</span> Protein-coding gene in the species Homo sapiens

cAMP-dependent protein kinase type II-beta regulatory subunit is an enzyme that in humans is encoded by the PRKAR2B gene.

<span class="mw-page-title-main">PHKG1</span> Protein-coding gene in the species Homo sapiens

Phosphorylase b kinase gamma catalytic chain, skeletal muscle isoform is an enzyme that in humans is encoded by the PHKG1 gene.

<span class="mw-page-title-main">G beta-gamma complex</span>

The G beta-gamma complex (Gβγ) is a tightly bound dimeric protein complex, composed of one Gβ and one Gγ subunit, and is a component of heterotrimeric G proteins. Heterotrimeric G proteins, also called guanosine nucleotide-binding proteins, consist of three subunits, called alpha, beta, and gamma subunits, or Gα, Gβ, and Gγ. When a G protein-coupled receptor (GPCR) is activated, Gα dissociates from Gβγ, allowing both subunits to perform their respective downstream signaling effects. One of the major functions of Gβγ is the inhibition of the Gα subunit.

<span class="mw-page-title-main">Protein phosphatase 1</span>

Protein phosphatase 1 (PP1) belongs to a certain class of phosphatases known as protein serine/threonine phosphatases. This type of phosphatase includes metal-dependent protein phosphatases (PPMs) and aspartate-based phosphatases. PP1 has been found to be important in the control of glycogen metabolism, muscle contraction, cell progression, neuronal activities, splicing of RNA, mitosis, cell division, apoptosis, protein synthesis, and regulation of membrane receptors and channels.

References

  1. 1 2 Stoker, H. Stephen (1 January 2015). General, Organic, and Biological Chemistry (7th ed.). Boston, MA: Cengage Learning. pp. 709–710. ISBN   978-1-305-68618-2 . Retrieved 15 April 2022.
  2. ↑ Smith, Michael B. (27 April 2020). Biochemistry: An Organic Chemistry Approach. Boca Raton: CRC Press. pp. 269–270. ISBN   978-1-351-25807-4 . Retrieved 15 April 2022.
  3. 1 2 Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2002). The Shape and Structure of Proteins. New York: Garland Science. Retrieved 15 April 2022.
  4. ↑ Kumar, A.; Evarsson, A.; Hol, W. G. J. (1999). "Multi-protein assemblies with point group symmetry". In Vijayan, M.; Yathindra, N.; Kolaskar, A. S. (eds.). Perspectives in Structural Biology: A Volume in Honour of G.N. Ramachandran. Hyderabad, India: Universities Press. pp. 449–466. ISBN   978-81-7371-254-8 . Retrieved 15 April 2022.
  5. ↑ Lesieur, Claire (18 June 2014). Oligomerization of Chemical and Biological Compounds. Croatia: Intech. pp. 240–241. ISBN   978-953-51-1617-2 . Retrieved 15 April 2022.
  6. ↑ Ahmad, Zulfiqar; Okafor, Florence; Azim, Sofiya; Laughlin, Thomas F. (2013). "ATP Synthase: A Molecular Therapeutic Drug Target for Antimicrobial and Antitumor Peptides". Current Medicinal Chemistry. 20 (15): 1956–1973. doi:10.2174/0929867311320150003. ISSN   0929-8673. PMC   4734648 . PMID   23432591.
  7. ↑ Jenkins, A. D.; Kratochvíl, P.; Stepto, R. F. T.; Suter, U. W. (1996). "Glossary of basic terms in polymer science (IUPAC Recommendations 1996)". Pure and Applied Chemistry . 68 (12): 2287–2311. doi: 10.1351/pac199668122287 .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. ↑ Liu, Shijie (7 April 2020). Bioprocess Engineering: Kinetics, Sustainability, and Reactor Design. Elsevier. p. 358. ISBN   978-0-12-822383-3 . Retrieved 15 April 2022.
  9. ↑ Dharan, Adarsh; Campbell, Edward M. (31 July 2018). "Role of Microtubules and Microtubule-Associated Proteins in HIV-1 Infection". Journal of Virology. 92 (16): e00085–18. doi:10.1128/JVI.00085-18. ISSN   0022-538X. PMC   6069196 . PMID   29899089.
  10. ↑ Søberg, Kristoffer; Skålhegg, Bjørn Steen (12 September 2018). "The Molecular Basis for Specificity at the Level of the Protein Kinase a Catalytic Subunit". Frontiers in Endocrinology. 9: 538. doi: 10.3389/fendo.2018.00538 . ISSN   1664-2392. PMC   6143667 . PMID   30258407.
  11. ↑ Daniel M, Peek GW, Tollefsbol TO (2012). "Regulation of the human catalytic subunit of telomerase (hTERT)". Gene . 498 (2): 135–46. doi:10.1016/j.gene.2012.01.095. PMC   3312932 . PMID   22381618.
  12. ↑ Carpenter CL, Duckworth BC, Auger KR, Cohen B, Schaffhausen BS, Cantley LC (November 1990). "Purification and characterization of phosphoinositide 3-kinase from rat liver". J. Biol. Chem. 265 (32): 19704–11. doi: 10.1016/S0021-9258(17)45429-9 . PMID   2174051.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.