PDBsum entry 2c3h

Carbohydrate-binding module

PDB id: 2c3h

Contents

Protein chains

(+ 2 more) 93 a.a. *

Ligands

GLC-GLC ×8

SO4 ×9

GLC

Waters ×804

* Residue conservation analysis

PDB id:

2c3h

Name:

Carbohydrate-binding module

Title:

Structure of cbm26 from bacillus halodurans amylase in complex with maltose

Structure:

Alpha-amylase g-6. Chain: a, b, c, d, e, f, g, h. Fragment: carbohydrate-binding module, residues 771-863. Synonym: family 26 carbohydrate-binding module. Engineered: yes

Source:

Bacillus halodurans. Organism_taxid: 272558. Strain: c-125. Atcc: baa-125. Expressed in: escherichia coli. Expression_system_taxid: 469008.

Resolution:

2.24Å R-factor: 0.207 R-free: 0.279

Authors:

A.B.Boraston,M.Healey,J.Klassen,E.Ficko-Blean,A.Lammerts Van Bueren, V.Law

Key ref:

A.B.Boraston et al. (2006). A structural and functional analysis of alpha-glucan recognition by family 25 and 26 carbohydrate-binding modules reveals a conserved mode of starch recognition. J Biol Chem, 281, 587-598. PubMed id: 16230347 DOI: 10.1074/jbc.M509958200

Date:

07-Oct-05 Release date: 17-Oct-05

Protein chains

Q9KFR4  (Q9KFR4_BACHD) -  Alpha-amylase G-6 from Halalkalibacterium halodurans (strain ATCC BAA-125 / DSM 18197 / FERM 7344 / JCM 9153 / C-125)

Seq: 958 a.a.

Struc: 93 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

DOI no: 10.1074/jbc.M509958200

J Biol Chem 281:587-598 (2006)

PubMed id: 16230347

A structural and functional analysis of alpha-glucan recognition by family 25 and 26 carbohydrate-binding modules reveals a conserved mode of starch recognition.

A.B.Boraston, M.Healey, J.Klassen, E.Ficko-Blean, A.Lammerts van Bueren, V.Law.

ABSTRACT

Starch-hydrolyzing enzymes lacking alpha-glucan-specific carbohydrate-binding modules (CBMs) typically have lowered activity on granular starch relative to their counterparts with CBMs. Thus, consideration of starch recognition by CBMs is a key factor in understanding granular starch hydrolysis. To this end, we have dissected the modular structure of the maltohexaose-forming amylase from Bacillus halodurans (C-125). This five-module protein comprises an N-terminal family 13 catalytic module followed in order by two modules of unknown function, a family 26 CBM (BhCBM26), and a family 25 CBM (BhCBM25). Here we present a comprehensive structure-function analysis of starch and alpha-glucooligosaccharide recognition by BhCBM25 and BhCBM26 using UV methods, isothermal titration calorimetry, and x-ray crystallography. The results reveal that the two CBMs bind alpha-glucooligosaccharides, particularly those containing alpha-1,6 linkages, with different affinities but have similar abilities to bind granular starch. Notably, these CBMs appear to recognize the same binding sites in granular starch. The enhanced affinity of the tandem CBMs for granular starch is suggested to be the main biological advantage for this enzyme to contain two CBMs. Structural studies of the native and ligand-bound forms of BhCBM25 and BhCBM26 show a structurally conserved mode of ligand recognition but through non-sequence-conserved residues. Comparison of these CBM structures with other starch-specific CBM structures reveals a generally conserved mode of starch recognition.

Selected figure(s)

Figure 5.
FIGURE 5. Phasing and structures of BhCBM25 and BhCBM26. A, anomalous difference peaks (red) and representative electron density (blue; 0.39 electrons/Å3) contoured around the iodotyrosine heavy atom sites used for SAD phasing of BhCBM25. B, anomalous difference peaks (red) and representative electron density (blue; 0.37 electrons/Å3) contoured around the cadmium sites used for SAD phasing of BhCBM26. C, the overall secondary structure of BhCBM25 as representative of the fold and topology of both BhCBM25 and BhCBM26. Selected amino acid side chains are shown in a "licorice" representation. Electron density maps are maximum likelihood (29)/ [A] (44) weighted 2F[o] - F[c] electron density maps.

Figure 6.
FIGURE 6. Observed electron density for maltotetraose bound to BhCBM25 in the P2[1] crystal form (A), maltotetraose bound to BhCBM25 in the P4[3]2[1]2 crystal form (symmetry-related molecules are colored blue and green) (B), and maltose bound to BhCBM26 (C). The mobile binding loop of BhCBM26 discussed throughout is shown in violet. Relevant amino acid side chains are shown in a "licorice" representation and labeled. All maps are maximum likelihood (29)/ [A] (44) weighted 2F[o] - F[c] electron density maps contoured at 1 (0.30, 0.15, and 0.14 electrons/Å3 in A, B, and C, respectively).

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2006, 281, 587-598) copyright 2006.

Figures were selected by an automated process.