Prosthetic group

A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being tightly linked to the apoprotein.

Not to be confused with the cosubstrate that binds to the enzyme apoenzyme (either a holoprotein or heteroprotein) by non-covalent binding a non-protein (non-amino acid)

This is a component of a conjugated protein that is required for the protein's biological activity.^[1] The prosthetic group may be organic (such as a vitamin, sugar, RNA, phosphate or lipid) or inorganic (such as a metal ion). Prosthetic groups are bound tightly to proteins and may even be attached through a covalent bond. They often play an important role in enzyme catalysis. A protein without its prosthetic group is called an apoprotein, while a protein combined with its prosthetic group is called a holoprotein. A non-covalently bound prosthetic group cannot generally be removed from the holoprotein without denaturating the protein. Thus, the term "prosthetic group" is a very general one and its main emphasis is on the tight character of its binding to the apoprotein. It defines a structural property, in contrast to the term "coenzyme" that defines a functional property.

Prosthetic groups are a subset of cofactors. Loosely bound metal ions and coenzymes are still cofactors, but are generally not called prosthetic groups.^[2][3][4] In enzymes, prosthetic groups are involved in the catalytic mechanism and required for activity. Other prosthetic groups have structural properties. This is the case for the sugar and lipid moieties in glycoproteins and lipoproteins or RNA in ribosomes. They can be very large, representing the major part of the protein in proteoglycans for instance.

The heme group in hemoglobin is a prosthetic group. Further examples of organic prosthetic groups are vitamin derivatives: thiamine pyrophosphate, pyridoxal-phosphate and biotin. Since prosthetic groups are often vitamins or made from vitamins, this is one of the reasons why vitamins are required in the human diet. Inorganic prosthetic groups are usually transition metal ions such as iron (in heme groups, for example in cytochrome c oxidase and hemoglobin), zinc (for example in carbonic anhydrase), copper (for example in complex IV of the respiratory chain) and molybdenum (for example in nitrate reductase).

List of prosthetic groups

The table below contains a list of some of the most common prosthetic groups.

Prosthetic group	Function	Distribution
Flavin mononucleotide ^[5]	Redox reactions	Bacteria, archaea and eukaryotes
Flavin adenine dinucleotide ^[5]	Redox reactions	Bacteria, archaea and eukaryotes
Pyrroloquinoline quinone ^[6]	Redox reactions	Bacteria
Pyridoxal phosphate ^[7]	Transamination, decarboxylation and deamination	Bacteria, archaea and eukaryotes
Biotin ^[8]	Carboxylation	Bacteria, archaea and eukaryotes
Methylcobalamin ^[9]	Methylation and isomerisation	Bacteria, archaea and eukaryotes
Thiamine pyrophosphate ^[10]	Transfer of 2-carbon groups, α cleavage	Bacteria, archaea and eukaryotes
Heme ^[11]	Oxygen binding and redox reactions	Bacteria, archaea and eukaryotes
Molybdopterin ^[12]^[13]	Oxygenation reactions	Bacteria, archaea and eukaryotes
Lipoic acid ^[14]	Redox reactions	Bacteria, archaea and eukaryotes
Cofactor F430	Methanogenesis	Archaea

References

1. de Bolster, M.W.G. (1997). . International Union of Pure and Applied Chemistry. Archived from the original on 2012-11-28. Retrieved 2007-10-30.
2. Metzler DE (2001) Biochemistry. The chemical reactions of living cells, 2nd edition, Harcourt, San Diego.
3. Nelson DL and Cox M.M (2000) Lehninger, Principles of Biochemistry, 3rd edition, Worth Publishers, New York
4. Campbell MK and Farrell SO (2009) Biochemistry, 6th edition, Thomson Brooks/Cole, Belmont, California
5. Joosten V, van Berkel WJ (2007). "Flavoenzymes". Curr Opin Chem Biol. 11 (2): 195–202. doi:10.1016/j.cbpa.2007.01.010. PMID 17275397.
6. Salisbury SA, Forrest HS, Cruse WB, Kennard O (1979). "A novel coenzyme from bacterial primary alcohol dehydrogenases". Nature. 280 (5725): 843–4. Bibcode:1979Natur.280..843S. doi:10.1038/280843a0. PMID 471057. S2CID 3094647.{{cite journal}}: CS1 maint: multiple names: authors list (link) PMID 471057
7. Eliot AC, Kirsch JF (2004). "Pyridoxal phosphate enzymes: mechanistic, structural, and evolutionary considerations". Annu. Rev. Biochem. 73: 383–415. doi:10.1146/annurev.biochem.73.011303.074021. PMID 15189147.
8. Jitrapakdee S, Wallace JC (2003). "The biotin enzyme family: conserved structural motifs and domain rearrangements". Curr. Protein Pept. Sci. 4 (3): 217–29. doi:10.2174/1389203033487199. PMID 12769720.
9. Banerjee R, Ragsdale SW (2003). "The many faces of vitamin B12: catalysis by cobalamin-dependent enzymes". Annu. Rev. Biochem. 72: 209–47. doi:10.1146/annurev.biochem.72.121801.161828. PMID 14527323. S2CID 37393683.
10. Frank RA, Leeper FJ, Luisi BF (2007). "Structure, mechanism and catalytic duality of thiamine-dependent enzymes". Cell. Mol. Life Sci. 64 (7–8): 892–905. doi:10.1007/s00018-007-6423-5. PMID 17429582. S2CID 20415735.{{cite journal}}: CS1 maint: multiple names: authors list (link)
11. Wijayanti N, Katz N, Immenschuh S (2004). "Biology of heme in health and disease". Curr. Med. Chem. 11 (8): 981–6. doi:10.2174/0929867043455521. PMID 15078160.{{cite journal}}: CS1 maint: multiple names: authors list (link)
12. Mendel RR, Hänsch R (2002). "Molybdoenzymes and molybdenum cofactor in plants". J. Exp. Bot. 53 (375): 1689–98. doi:10.1093/jxb/erf038. PMID 12147719.
13. Mendel RR, Bittner F (2006). "Cell biology of molybdenum". Biochim. Biophys. Acta. 1763 (7): 621–35. doi:10.1016/j.bbamcr.2006.03.013. PMID 16784786.
14. Bustamante J, Lodge JK, Marcocci L, Tritschler HJ, Packer L, Rihn BH (1998). "Alpha-lipoic acid in liver metabolism and disease". Free Radic. Biol. Med. 24 (6): 1023–39. doi:10.1016/S0891-5849(97)00371-7. PMID 9607614.{{cite journal}}: CS1 maint: multiple names: authors list (link)

External links

• Cofactors PowerPoint lecture