PDBsum entry: 1sma

Hydrolase

PDB-id: 1sma

Biological unit* = asymmetric unit, as shown
(*as deduced by PQS)

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Protein chains

588 a.a. *

Waters ×191

* Residue conservation analysis

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Clefts Calculation

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PDB id:

1sma

Name:

Hydrolase

Title:

Crystal structure of a maltogenic amylase

Structure:

Maltogenic amylase. Chain: a, b. Fragment: n-domain, barrel, c-domain

Source:

Thermus sp. Im6501. Organism_taxid: 75891. Strain: m6501

Biological unit:

Dimer (from PQS)

UniProt:

Chains A, B: O69007 (O69007_9DEIN)

Seq:

Struc:

Seq:

Struc:

Seq:

588 a.a.

Struc:

588 a.a.

Key:	PfamA domain
Secondary structure	CATH domain

Resolution:

2.80Å

R-factor:

0.209

R-free:

0.267

Authors:

J.S.Kim,S.S.Cha,B.H.Oh

Key ref:

J.S.Kim et al. (1999). Crystal structure of a maltogenic amylase provides insights into a catalytic versatility.. J Biol Chem, 274, 26279-26286. [PubMed id: 10473583] [DOI: 10.1074/jbc.274.37.26279]

Date:

21-Apr-99

Release date:

26-Apr-00

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Clefts

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Key reference

DOI no: 10.1074/jbc.274.37.26279

J Biol Chem 274:26279-26286 (1999)

PubMed id: 10473583

Crystal structure of a maltogenic amylase provides insights into a catalytic versatility.

J.S.Kim, S.S.Cha, H.J.Kim, T.J.Kim, N.C.Ha, S.T.Oh, H.S.Cho, M.J.Cho, M.J.Kim, H.S.Lee, J.W.Kim, K.Y.Choi, K.H.Park, B.H.Oh.

ABSTRACT

Amylases catalyze the hydrolysis of starch material and play central roles in carbohydrate metabolism. Compared with many different amylases that are able to hydrolyze only alpha-D-(1,4)-glycosidic bonds, maltogenic amylases exhibit catalytic versatility: hydrolysis of alpha-D-(1,4)- and alpha-D-(1,6)-glycosidic bonds and transglycosylation of oligosaccharides to C3-, C4-, or C6-hydroxyl groups of various acceptor mono- or disaccharides. It has been speculated that the catalytic property of the enzymes is linked to the additional approximately 130 residues at the N terminus that are absent in other typical alpha-amylases. The crystal structure of a maltogenic amylase from a Thermus strain was determined at 2.8 A. The structure, an analytical centrifugation, and a size exclusion column chromatography proved that the enzyme is a dimer in solution. The N-terminal segment of the enzyme folds into a distinct domain and comprises the enzyme active site together with the central (alpha/beta)(8) barrel of the adjacent subunit. The active site is a narrow and deep cleft suitable for binding cyclodextrins, which are the preferred substrates to other starch materials. At the bottom of the active site cleft, an extra space, absent in the other typical alpha-amylases, is present whose size is comparable with that of a disaccharide. The space is most likely to host an acceptor molecule for the transglycosylation and to allow binding of a branched oligosaccharide for hydrolysis of alpha-D-(1,4)-glycosidic or alpha-D-(1,6)-glycosidic bond. The (alpha/beta)(8) barrel of the enzyme is the preserved scaffold in all the known amylases. The structure represents a novel example of how an enzyme acquires a different substrate profile and a catalytic versatility from a common active site and represents a framework for explaining the catalytic activities of transglycosylation and hydrolysis of alpha-D-(1,6)-glycosidic bond.

Selected figure(s)

Figure 4.
Fig. 4. Schematic drawings of products from reaction of acarbose with ThMA . Acarbose is hydrolyzed to PTS and glucose. Three different products can be generated by transglycosylation of PTS to glucose. One of those generated by -D-(1,4)-transglycosylation is acarbose. The activity of -D-(1,4)-transglycosylation can be detected by using an acceptor molecule such as -methylglucoside.

Figure 6.
Fig. 6. Proposed mechanism for competition of transglycosylation and hydrolysis reaction at the active site of ThMA . A proposal for a double-displacement reaction is followed. The third conserved residue Asp-424, which may play a role in raising the pK[a] of Glu-357 (30), is not drawn.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (1999, 274, 26279-26286) copyright 1999.

Figures were selected by an automated process.