Functional and Structural Characterization of a Novel Isoamylase from Ostreococcus tauri and Role of the N-Terminal Domain

Nicolas Hedín1, Julieta Barchiesi1, Diego F. Gomez-Casati1, *, María V. Busi1, *
1 Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), CONICET - Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina

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© 2020 Hedín et al

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: ( This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), CONICET - Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina; Fax: +54-0341-4370044; Tel: +54-0341-4371955; E-mails:,



The debranching starch enzymes, isoamylase 1 and 2 are well-conserved enzymes present in almost all the photosynthetic organisms. These enzymes are involved in the crystallization process of starch and are key components which remove misplaced α-1,6 ramifications on the final molecule.


In this work, we performed a functional and structural study of a novel isoamylase from Ostreococcus tauri.


We identified conserved amino acid residues possibly involved in catalysis. We also identified a region at the N-terminal end that resembles a Carbohydrate Binding Domain (CBM), which is more related to the family CBM48, but has no spatial conservation of the residues involved in carbohydrate binding.


The cloning, expression and biochemical characterization of this N-terminal region confirmed that it binds to polysaccharides, showing greater capacity for binding to amylopectin rather than total starch or amylose.


This module could be a variant of the CBM48 family or it could be classified within a new CBM family.

Keywords: Carbohydrate Binding Domain (CBM), Debranching starch enzymes, Amino acid residues, Polysaccharides, Biochemical characterization, Carbohydrates.