Small angle X-ray studies reveal that Aspergillus niger glucoamylase has a defined extended conformation and can form dimers in solution.

Full Abstract

The industrially important glucoamylase 1 is an exo-acting glycosidase with substrate preference for alpha-1,4 and alpha-1,6 linkages at non-reducing ends of starch. It consists of a starch binding and a catalytic domain interspersed by a highly glycosylated polypeptide linker. The linker function is poorly understood and structurally undescribed, and data regarding domain organization and intramolecular functional cooperativity are conflicting or non-comprehensive. Here, we report a combined small angle x-ray scattering and calorimetry study of Aspergillus niger glucoamylase 1, glucoamylase 2, which lacks a starch binding domain, and an engineered low-glycosylated variant of glucoamylase 1 with a short linker. Low resolution solution structures show that the linker adopts a compact structure rendering a well defined extended overall conformation to glucoamylase. We demonstrate that binding of a short heterobidentate inhibitor simultaneously directed toward the catalytic and starch binding domains causes dimerization of glucoamylase and not, as suggested previously, an intramolecular conformational rearrangement mediated by linker flexibility. Our results suggest that glucoamylase functions via transient dimer formation during hydrolysis of insoluble substrates and address the question of the cooperative effect of starch binding and hydrolysis.

Author information

Author/s: Jørgensen, Anders Dysted (AD); Nøhr, Jane (J); Kastrup, Jette Sandholm (JS); Gajhede, Michael (M); Sigurskjold, Bent W (BW); Sauer, Jørgen (J); Svergun, Dmitri I (DI); Svensson, Birte (B); Vestergaard, Bente (B);

Affiliation: Department of Medicinal Chemistry, University of Copenhagen, Copenhagen, Denmark.

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: The Journal of biological chemistry (J Biol Chem), published in United States. (Language: eng)

Reference: 2008-May; vol 283 (issue 21) : pp 14772-80

Dates: Created 2008/05/19; Completed 2008/07/18; Revised 2008/11/21;

PMID: 18378674, status: MEDLINE (last retrieved date: 2/18/2009)

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