The crystal structure of Thermotoga maritima maltosyltransferase and its implications for the molecular basis of the novel transfer specificity

Anna Roujeinikova, Carsten Raasch, Jacky Burke, Patrick J. Baker, Wolfgang Liebl, David W. Rice

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15 Citations (Scopus)

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 α-1,4-linked glucans or malto-oligosaccharides to other α-1,4-linked glucans, malto-oligosaccharides or glucose. It belongs to the glycoside hydrolase family 13, which represents a large group of (β/α)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 Å and 2.1 Å 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 (β/α)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.

Original languageEnglish
Pages (from-to)119-131
Number of pages13
JournalJournal of Molecular Biology
Volume312
Issue number1
DOIs
Publication statusPublished - 7 Sep 2001
Externally publishedYes

Keywords

  • α-amylase family
  • Maltosyltransferase
  • Structure comparison
  • Thermotoga maritima
  • Transfer specificity

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