Glycoside hydrolase family 22 explained

In molecular biology, glycoside hydrolase family 22 is a family of glycoside hydrolases., which are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families.[1] [2] [3] This classification is available on the CAZy web site,[4] [5] and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.[6] [7]

Glycoside hydrolase family 22 CAZY GH_22 comprises lysozyme type C lysozyme type i and alpha-lactalbumins. Asp and/or the carbonyl oxygen of the C-2 acetamido group of the substrate acts as the catalytic nucleophile/base.

Alpha-lactalbumin,[8] [9] is a milk protein that acts as the regulatory subunit of lactose synthetase, acting to promote the conversion of galactosyltransferase to lactose synthase, which is essential for milk production. In the mammary gland, alpha-lactalbumin changes the substrate specificity of galactosyltransferase from N-acetylglucosamine to glucose.

Lysozymes act as bacteriolytic enzymes by hydrolyzing the beta(1->4) bonds between N-acetylglucosamine and N-acetylmuramic acid in the peptidoglycan of bacterial cell walls. It has also been recruited for a digestive role in certain ruminants and colobine monkeys.[10] There are at least five different classes of lysozymes:[11] C (chicken type), G (goose type), phage-type (T4), fungi (Chalaropsis), and bacterial (Bacillus subtilis). There are few similarities in the sequences of the different types of lysozymes.

Lysozyme type C and alpha-lactalbumin are similar both in terms of primary sequence and structure, and probably evolved from a common ancestral protein.[12] Around 35 to 40% of the residues are conserved in both proteins as well as the positions of the four disulphide bonds. There is, however, no similarity in function. Another significant difference between the two enzymes is that all lactalbumins have the ability to bind calcium,[13] while this property is restricted to only a few lysozymes.[14]

The binding site was deduced using high resolution X-ray structure analysis and was shown to consist of three aspartic acid residues. It was first suggested that calcium bound to lactalbumin stabilised the structure, but recently it has been claimed that calcium controls the release of lactalbumin from the golgi membrane and that the pattern of ion binding may also affect the catalytic properties of the lactose synthetase complex.

Notes and References

  1. Henrissat B, Callebaut I, Fabrega S, Lehn P, Mornon JP, Davies G . Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases . Proceedings of the National Academy of Sciences of the United States of America . 92 . 15 . 7090–4 . July 1995 . 7624375 . 41477 . 10.1073/pnas.92.15.7090 . 1995PNAS...92.7090H . free .
  2. Davies G, Henrissat B . Structures and mechanisms of glycosyl hydrolases . Structure . 3 . 9 . 853–9 . September 1995 . 8535779 . 10.1016/S0969-2126(01)00220-9 . free .
  3. Henrissat B, Bairoch A . Updating the sequence-based classification of glycosyl hydrolases . The Biochemical Journal . 316 . Pt 2 . 695–6 . June 1996 . 8687420 . 1217404 . 10.1042/bj3160695.
  4. Web site: Home. CAZy.org. en. 2018-03-06.
  5. Lombard V, Golaconda Ramulu H, Drula E, Coutinho PM, Henrissat B . The carbohydrate-active enzymes database (CAZy) in 2013 . Nucleic Acids Research . 42 . Database issue . D490-5 . January 2014 . 24270786 . 10.1093/nar/gkt1178 . 3965031 .
  6. Web site: Glycoside Hydrolase Family 22. CAZypedia.org. en. 2018-03-06.
  7. Ten years of CAZypedia: a living encyclopedia of carbohydrate-active enzymes . Glycobiology . 28 . 1 . 3–8 . December 2018 . 29040563 . 10.1093/glycob/cwx089 . CAZypedia Consortium . free . 21.11116/0000-0003-B7EB-6 . free .
  8. Shewale JG, Sinha SK, Brew K . Evolution of alpha-lactalbumins. The complete amino acid sequence of the alpha-lactalbumin from a marsupial (Macropus rufogriseus) and corrections to regions of sequence in bovine and goat alpha-lactalbumins . The Journal of Biological Chemistry . 259 . 8 . 4947–56 . April 1984 . 10.1016/S0021-9258(17)42938-3 . 6715332 . free .
  9. Hall L, Campbell PN . Alpha-lactalbumin and related proteins: a versatile gene family with an interesting parentage . Essays in Biochemistry . 22 . 1–26 . 1986 . 3104032 .
  10. Irwin DM, Wilson AC . Multiple cDNA sequences and the evolution of bovine stomach lysozyme . The Journal of Biological Chemistry . 264 . 19 . 11387–93 . July 1989 . 10.1016/S0021-9258(18)60476-4 . 2738070 . free .
  11. Kamei K, Hara S, Ikenaka T, Murao S . Amino acid sequence of a lysozyme (B-enzyme) from Bacillus subtilis YT-25 . Journal of Biochemistry . 104 . 5 . 832–6 . November 1988 . 3148618 . 10.1093/oxfordjournals.jbchem.a122558.
  12. Nitta K, Sugai S . The evolution of lysozyme and alpha-lactalbumin . European Journal of Biochemistry . 182 . 1 . 111–8 . June 1989 . 2731545 . 10.1111/j.1432-1033.1989.tb14806.x . free .
  13. Stuart DI, Acharya KR, Walker NP, Smith SG, Lewis M, Phillips DC . Alpha-lactalbumin possesses a novel calcium binding loop . Nature . 324 . 6092 . 84–7 . 1986 . 3785375 . 10.1038/324084a0 . 1986Natur.324...84S . 4349973 .
  14. Nitta K, Tsuge H, Sugai S, Shimazaki K . The calcium-binding property of equine lysozyme . FEBS Letters . 223 . 2 . 405–8 . November 1987 . 3666156 . 10.1016/0014-5793(87)80328-9 . 12630658 . free .

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Glycoside hydrolase family 22".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy.