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636 a.a.
Key reference
DOI no: 10.1006/jmbi.2001.4944 J Mol Biol 312:119-131 (2001) PubMed id: 11545590
The crystal structure of Thermotoga maritima maltosyltransferase and its implications for the molecular basis of the novel transfer specificity. A.Roujeinikova, C.Raasch, J.Burke, P.J.Baker, W.Liebl, D.W.Rice. ABSTRACT
Maltosyltransferase (MTase) from the hyperthermophile Thermotoga maritima represents a novel maltodextrin glycosyltransferase acting on starch and malto-oligosaccharides. It catalyzes the transfer of maltosyl units from alpha-1,4-linked glucans or malto-oligosaccharides to other alpha-1,4-linked glucans, malto-oligosaccharides or glucose. It belongs to the glycoside hydrolase family 13, which represents a large group of (beta/alpha)(8) barrel proteins sharing a similar active site structure. The crystal structures of MTase and its complex with maltose have been determined at 2.4 A and 2.1 A resolution, respectively. MTase is a homodimer, each subunit of which consists of four domains, two of which are structurally homologous to those of other family 13 enzymes. The catalytic core domain has the (beta/alpha)(8) barrel fold with the active-site cleft formed at the C-terminal end of the barrel. Substrate binding experiments have led to the location of two distinct maltose-binding sites; one lies in the active-site cleft, covering subsites -2 and -1; the other is located in a pocket adjacent to the active-site cleft. The structure of MTase, together with the conservation of active-site residues among family 13 glycoside hydrolases, are consistent with a common double-displacement catalytic mechanism for this enzyme. Analysis of maltose binding in the active site reveals that the transfer of dextrinyl residues longer than a maltosyl unit is prevented by termination of the active-site cleft after the -2 subsite by the side-chain of Lys151 and the stretch of residues 314-317, providing an explanation for the strict transfer specificity of MTase.
Selected figure(s)
Figure 2.
Figure 2. (a) Stereoview of the superposition of the C-terminal domains of MTase (red), B. circulans CGTase (green) and B. cereus oligo-1,6-glucosidase (blue). The N and C-terminal ends of the domains are labelled. (b) Stereoview of the superposition of the C-terminal domain of MTase (red) and the CBD from the cellulosomal scaffoldin subunit of C. thermocellum (see the text). The residues of the CBD forming the planar strip proposed to interact with crystalline cellulose[31] are shown.Figure 4.
Figure 4. Stereoview of the superposition of the invariant residues in the active sites of TAKA amylase A (green), B. circulans CGTase (orange) and B. cereus oligo-1,6-glucosidase (red) and the corresponding residues in MTase (blue). Included are the maltose molecules observed in MTase (grey lines) occupying subsites -2 and -1, and the -2 and -1 sugar units of the substrate bound to CGTase (orange) and the acarbose bound to TAKA amylase A (green), respectively.The above figures are reprinted by permission from Elsevier: J Mol Biol (2001, 312, 119-131) copyright 2001. Figures were selected by an automated process.
Literature references that cite this PDB file's key reference
PubMed id Reference
17459873 M.Nagae, A.Tsuchiya, T.Katayama, K.Yamamoto, S.Wakatsuki, and R.Kato (2007).
Structural basis of the catalytic reaction mechanism of novel 1,2-alpha-L-fucosidase from Bifidobacterium bifidum.J Biol Chem, 282, 18497-18509.
PDB codes: 2eab 2eac 2ead 2eae
17064285 S.B.Conners, E.F.Mongodin, M.R.Johnson, C.I.Montero, K.E.Nelson, and R.M.Kelly (2006).
Microbial biochemistry, physiology, and biotechnology of hyperthermophilic Thermotoga species.FEMS Microbiol Rev, 30, 872-905.
12581203 S.Janecek, B.Svensson, and E.A.MacGregor (2003).
Relation between domain evolution, specificity, and taxonomy of the alpha-amylase family members containing a C-terminal starch-binding domain.Eur J Biochem, 270, 635-645. The most recent references are shown first. Citation data come partly from CiteXplore and partly from an automated harvesting procedure. Note that this is likely to be only a partial list as not all journals are covered by either method. However, we are continually building up the citation data so more and more references will be included with time. Where a reference describes a PDB structure, the PDB codes are shown on the right.
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