Flavoprotein Explained

Symbol:	Flavoprotein
Flavoprotein
Pfam:	PF02441
Interpro:	IPR003382
Scop:	1e20

Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin. These proteins are involved in a wide array of biological processes, including removal of radicals contributing to oxidative stress, photosynthesis, and DNA repair. The flavoproteins are some of the most-studied families of enzymes.

Flavoproteins have either FMN (flavin mononucleotide) or FAD (flavin adenine dinucleotide) as a prosthetic group or as a cofactor. The flavin is generally tightly bound (as in adrenodoxin reductase, wherein the FAD is buried deeply).^[1] About 5-10% of flavoproteins have a covalently linked FAD.^[2] Based on the available structural data, FAD-binding sites can be divided into more than 200 different types.^[3]

90 flavoproteins are encoded in the human genome; about 84% require FAD and around 16% require FMN, whereas 5 proteins require both.^[4] Flavoproteins are mainly located in the mitochondria. Of all flavoproteins, 90% perform redox reactions and the other 10% are transferases, lyases, isomerases, ligases.^[5]

Discovery

Flavoproteins were first mentioned in 1879, when they isolated as a bright-yellow pigment from cow's milk. They were initially termed lactochrome. By the early 1930s, this same pigment had been isolated from a range of sources, and recognised as a component of the vitamin B complex. Its structure was determined and reported in 1935 and given the name riboflavin, derived from the ribityl side chain and yellow colour of the conjugated ring system.^[6]

The first evidence for the requirement of flavin as an enzyme cofactor came in 1935. Hugo Theorell and coworkers showed that a bright-yellow-coloured yeast protein, identified previously as essential for cellular respiration, could be separated into apoprotein and a bright-yellow pigment. Neither apoprotein nor pigment alone could catalyse the oxidation of NADH, but mixing of the two restored the enzyme activity. However, replacing the isolated pigment with riboflavin did not restore enzyme activity, despite being indistinguishable under spectroscopy. This led to the discovery that the protein studied required not riboflavin but flavin mononucleotide to be catalytically active.^[7]

Similar experiments with D-amino acid oxidase^[8] led to the identification of flavin adenine dinucleotide (FAD) as a second form of flavin utilised by enzymes.^[9]

Examples

The flavoprotein family contains a diverse range of enzymes, including:

• Adrenodoxin reductase that is involved in steroid hormone synthesis in vertebrate species, and has a ubiquitous distribution in metazoa and prokaryotes
• Cytochrome P450 reductase that is a redox partner of cytochrome P450 proteins located in endoplasmic reticulum^{[10] [11]}
• Epidermin biosynthesis protein, EpiD, which has been shown to be a flavoprotein that binds FMN. This enzyme catalyses the removal of two reducing equivalents from the cysteine residue of the C-terminal meso-lanthionine of epidermin to form a --C

C-- double bond^[12]

• The B chain of dipicolinate synthase, an enzyme which catalyses the formation of dipicolinic acid from dihydroxydipicolinic acid^[13]
• Phenylacrylic acid decarboxylase, an enzyme which confers resistance to cinnamic acid in yeast^[14]
• Phototropin and cryptochrome, light-sensing proteins^[15]

References

1. Hanukoglu I . Conservation of the Enzyme-Coenzyme Interfaces in FAD and NADP Binding Adrenodoxin Reductase-A Ubiquitous Enzyme . Journal of Molecular Evolution . 85 . 5 . 205–218 . 2017 . 29177972 . 10.1007/s00239-017-9821-9 . 2017JMolE..85..205H . 7120148 .
2. Abbas. Charles A.. Sibirny. Andriy A.. 2011-06-01. Genetic Control of Biosynthesis and Transport of Riboflavin and Flavin Nucleotides and Construction of Robust Biotechnological Producers. Microbiology and Molecular Biology Reviews. en. 75. 2. 321–360. 10.1128/MMBR.00030-10. 1092-2172. 3122625. 21646432.
3. Garma. Leonardo D.. Medina. Milagros. Juffer. André H.. 2016-11-01. Structure-based classification of FAD binding sites: A comparative study of structural alignment tools. Proteins: Structure, Function, and Bioinformatics. en. 84. 11. 1728–1747. 10.1002/prot.25158. 27580869. 26066208. 1097-0134.
4. Lienhart. Wolf-Dieter. Gudipati. Venugopal. Macheroux. Peter. 2013-07-15. The human flavoproteome. Archives of Biochemistry and Biophysics. 535. 2. 150–162. 10.1016/j.abb.2013.02.015. 3684772. 23500531.
5. Macheroux. Peter. Kappes. Barbara. Ealick. Steven E.. 2011-08-01. Flavogenomics – a genomic and structural view of flavin-dependent proteins. FEBS Journal. en. 278. 15. 2625–2634. 10.1111/j.1742-4658.2011.08202.x. 21635694. 22220250. 1742-4658. free.
6. 10961912 . The chemical and biological versatility of riboflavin . 2000 . Massey . V . Biochemical Society Transactions . 28 . 4 . 283–96 . 10.1042/0300-5127:0280283.
7. Theorell . H. . 1935 . Preparation in pure state of the effect group of yellow enzymes . Biochemische Zeitschrift . 275 . 344–46.
8. Warburg . O. . Christian . W. . 1938 . Isolation of the prosthetic group of the amino acid oxydase . Biochemische Zeitschrift . 298 . 150–68.
9. 10.1039/JR9540000046 . Nucleotides. Part XXV. A synthesis of flavin?adenine dinucleotide . Journal of the Chemical Society . 46–52 . 1954 . Christie . S. M. H. . Kenner . G. W. . Todd . A. R. .
10. 2013-05-01. NADPH P450 oxidoreductase: Structure, function, and pathology of diseases. Pharmacology & Therapeutics. en. 138. 2. 229–254. 10.1016/j.pharmthera.2013.01.010. 0163-7258. Pandey . Amit V. . Flück . Christa E. . 23353702 .
11. Jensen. Simon Bo. Thodberg. Sara. Parween. Shaheena. Moses. Matias E.. Hansen. Cecilie C.. Thomsen. Johannes. Sletfjerding. Magnus B.. Knudsen. Camilla. Del Giudice. Rita. Lund. Philip M.. Castaño. Patricia R.. 2021-04-15. Biased cytochrome P450-mediated metabolism via small-molecule ligands binding P450 oxidoreductase. Nature Communications. en. 12. 1. 2260. 10.1038/s41467-021-22562-w . 33859207 . 8050233 . 2021NatCo..12.2260J . 2041-1723. free.
12. 1644762 . 206373 . 1992 . Kupke . T . Purification and characterization of EpiD, a flavoprotein involved in the biosynthesis of the lantibiotic epidermin . Journal of Bacteriology . 174 . 16 . 5354–61 . Stevanović . S . Sahl . H. G. . Götz . F . 10.1128/jb.174.16.5354-5361.1992 .
13. 10.1006/jmbi.1993.1403 . 8345520 . Cloning, DNA Sequence, Functional Analysis and Transcriptional Regulation of the Genes Encoding Dipicolinic Acid Synthetase Required for Sporulation in Bacillus subtilis . Journal of Molecular Biology . 232 . 2 . 468–83 . 1993 . Daniel . R.A. . Errington . J. .
14. 10.1016/0378-1119(94)90363-8 . 8181743 . PAD1 encodes phenylacrylic acid decarboxylase which confers resistance to cinnamic acid in Saccharomyces cerevisiae . Gene . 142 . 1 . 107–12 . 1994 . Clausen . Monika . Lamb . Christopher J. . Megnet . Roland . Doerner . Peter W. .
15. Zhuang . Bo . Liebl . Ursula . Vos . Marten H. . 2022-05-05 . Flavoprotein Photochemistry: Fundamental Processes and Photocatalytic Perspectives . The Journal of Physical Chemistry B . en . 126 . 17 . 3199–3207 . 10.1021/acs.jpcb.2c00969 . 35442696 . 248296520 . 1520-6106.

External links

• The menu "science" of the program STRAP provides A comprehensive collection of all flavo-proteins with known 3D-structure. It compares the protein structures to elucidate phylogenetic relationships.