Glycoside Hydrolase Family 77

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Glycoside Hydrolase Family GH77
Clan GH-H
Mechanism retaining
Active site residues known
CAZy DB link

Substrate specificities

Glycoside hydrolase family GH77 is the member of the α-amylase clan GH-H [1], together with GH13 and GH70 [2]. The family is monospecific with the 4-α-glucanotransferase (EC, that is known as disproportionating enzyme (D-enzyme) in plants [3] or amylomaltase in bacteria [4] and archaeons [5]. Around 2,000 members [6] originates almost exclusively from Bacteria; and the family contains also a few tens of additional sequences from each Archaea and Eucarya (plants and green algae).

Amylomaltase catalyses the glucan-chain transfer from one α-1,4-glucan to another α-1,4-glucan (or to 4-hydroxyl group of glucose) or within a single linear glucan molecule to produce a cyclic α-1,4-glucan with degree of polymerization starting from 17 [3, 4, 5]. Cyclodextrin glucanotransferase, a member of the α-amylase family GH13, also produces cyclic α-1,4-glucans, but with a small degree of polymerization (6-8), called cyclodextrins [7].

Five tertiary structures have already been determined and only several tens enzymes have been biochemically characterized [6]. The main structural feature that discriminates the family GH77 amylomaltases from typical α-amylase family GH13 members is the lack of domain C [8] that succeeds the catalytic (β/α)8-barrel in the family GH13. The eight-fold symmetry of the catalytic barrel is disrupted by several insertions between the barrel β-strands that form the so-called subdomains B1, B2 and B3 [8]. Subdomain B1 consists of a highly twisted four-stranded antiparallel β-sheet with two α-helices and it is also present in other enzymes from the α-amylase clan GH-H (known as domain B). Subdomain B2 has predominantly an α-helical structure and it is unique to amylomaltases. Subdomain B3 could have a role of domain C from the α-amylase family [8].

Interestingly, primary structures of amylomaltases from borreliae contain unique sequence features [9], i.e. natural mutations in functionally important positions, such as extremely well-conserved and functional arginine in position i-2 with respect to the catalytic nucleophile is replaced naturally by a lysine. It is worth mentioning that this arginine positioned two residues before the catalytic nucleophile in the conserved sequence region II was considered to belong to the four residues conserved invariantly throughout the α-amylase family [10]. Its substitution is therefore of a special interest because the GH77 protein from Borrelia burgdorferi does exhibit the real amylomaltase activity [11]. Since, however, the lysine could eventually play the role of the original arginine, it is not possible to say unambiguously that the catalytic triad alone is enough for a GH-H protein to be a real functional member of the α-amylase family.

Kinetics and Mechanism

The GH77 members employ the retaining reaction mechanism as used in the family GH13.

Catalytic Residues

They fold into a (β/α)8-barrel with the catalytic machinery consisting of a strand β4-aspartic acid (catalytic nucleophile), β5-glutamic acid (proton donor) and β7-aspartic acid (transition-state stabilizer), and they share their own 4-7 characteristic conserved sequence regions.

Three-dimensional structures

Family Firsts

First stereochemistry determination
Cite some reference here, with a short (1-2 sentence) explanation.
First catalytic nucleophile identification
Cite some reference here, with a short (1-2 sentence) explanation.
First general acid/base residue identification
Cite some reference here, with a short (1-2 sentence) explanation.
First 3-D structure
The first 3-D structure of a GH77 member was that of the amylomaltase from Thermus aquaticus solved first as a free enzyme [8] and subsequently also as a complex with acarbose [12].


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  2. MacGregor EA, Janecek S, and Svensson B. (2001). Relationship of sequence and structure to specificity in the alpha-amylase family of enzymes. Biochim Biophys Acta. 2001;1546(1):1-20. DOI:10.1016/s0167-4838(00)00302-2 | PubMed ID:11257505 [MacGregor2001]
  3. Takaha T, Yanase M, Okada S, and Smith SM. (1993). Disproportionating enzyme (4-alpha-glucanotransferase; EC of potato. Purification, molecular cloning, and potential role in starch metabolism. J Biol Chem. 1993;268(2):1391-6. | Google Books | Open Library PubMed ID:7678257 [Takaha1993]
  4. Terada Y, Fujii K, Takaha T, and Okada S. (1999). Thermus aquaticus ATCC 33923 amylomaltase gene cloning and expression and enzyme characterization: production of cycloamylose. Appl Environ Microbiol. 1999;65(3):910-5. DOI:10.1128/AEM.65.3.910-915.1999 | PubMed ID:10049841 [Terada1999]
  5. Kaper T, Talik B, Ettema TJ, Bos H, van der Maarel MJ, and Dijkhuizen L. (2005). Amylomaltase of Pyrobaculum aerophilum IM2 produces thermoreversible starch gels. Appl Environ Microbiol. 2005;71(9):5098-106. DOI:10.1128/AEM.71.9.5098-5106.2005 | PubMed ID:16151092 [Kaper2005]
  6. Lombard V, Golaconda Ramulu H, Drula E, Coutinho PM, and Henrissat B. (2014). The carbohydrate-active enzymes database (CAZy) in 2013. Nucleic Acids Res. 2014;42(Database issue):D490-5. DOI:10.1093/nar/gkt1178 | PubMed ID:24270786 [Lombard2014]
  7. Leemhuis H, Kelly RM, and Dijkhuizen L. (2010). Engineering of cyclodextrin glucanotransferases and the impact for biotechnological applications. Appl Microbiol Biotechnol. 2010;85(4):823-35. DOI:10.1007/s00253-009-2221-3 | PubMed ID:19763564 [Leemhuis2010]
  8. Przylas I, Tomoo K, Terada Y, Takaha T, Fujii K, Saenger W, and Sträter N. (2000). Crystal structure of amylomaltase from thermus aquaticus, a glycosyltransferase catalysing the production of large cyclic glucans. J Mol Biol. 2000;296(3):873-86. DOI:10.1006/jmbi.1999.3503 | PubMed ID:10677288 [Przylas2000a]
  9. Machovic M, and Janecek S. The invariant residues in the α-amylase family: just the catalytic triad. Biologia 2003; 58(6) 1127-32. (PDF)

  10. Janecek S. How many conserved sequence regions are there in the α-amylase family? Biologia 2002; 57(Suppl. 11) 29-41. (PDF)

  11. Godány A, Vidová B, and Janecek S. (2008). The unique glycoside hydrolase family 77 amylomaltase from Borrelia burgdorferi with only catalytic triad conserved. FEMS Microbiol Lett. 2008;284(1):84-91. DOI:10.1111/j.1574-6968.2008.01191.x | PubMed ID:18494783 [Godany2008]
  12. Przylas I, Terada Y, Fujii K, Takaha T, Saenger W, and Sträter N. (2000). X-ray structure of acarbose bound to amylomaltase from Thermus aquaticus. Implications for the synthesis of large cyclic glucans. Eur J Biochem. 2000;267(23):6903-13. DOI:10.1046/j.1432-1033.2000.01790.x | PubMed ID:11082203 [Przylas2000b]
  13. Srisimarat W, Murakami S, Pongsawasdi P, and Krusong K. (2013). Crystallization and preliminary X-ray crystallographic analysis of the amylomaltase from Corynebacterium glutamicum. Acta Crystallogr Sect F Struct Biol Cryst Commun. 2013;69(Pt 9):1004-6. DOI:10.1107/S1744309113020319 | PubMed ID:23989149 [Srisimarat2013]
  14. Hoon-Hanks LL, Morton EA, Lybecker MC, Battisti JM, Samuels DS, and Drecktrah D. (2012). Borrelia burgdorferi malQ mutants utilize disaccharides and traverse the enzootic cycle. FEMS Immunol Med Microbiol. 2012;66(2):157-65. DOI:10.1111/j.1574-695X.2012.00996.x | PubMed ID:22672337 [Hoon-Hanks2012]
  15. Jung JH, Jung TY, Seo DH, Yoon SM, Choi HC, Park BC, Park CS, and Woo EJ. (2011). Structural and functional analysis of substrate recognition by the 250s loop in amylomaltase from Thermus brockianus. Proteins. 2011;79(2):633-44. DOI:10.1002/prot.22911 | PubMed ID:21117235 [Jung2011]
  16. van der Maarel MJ and Leemhuis H. (2013). Starch modification with microbial alpha-glucanotransferase enzymes. Carbohydr Polym. 2013;93(1):116-21. DOI:10.1016/j.carbpol.2012.01.065 | PubMed ID:23465909 [vanderMaarel2013]

All Medline abstracts: PubMed