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93 a.a.
Key reference
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)/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.
Literature references that cite this PDB file's key reference
PubMed id Reference
19682075 C.Christiansen, M.Abou Hachem, S.Janecek, A.Viksø-Nielsen, A.Blennow, and B.Svensson (2009).
The carbohydrate-binding module family 20--diversity, structure, and function.FEBS J, 276, 5006-5029.
19052787 R.Rodríguez-Sanoja, N.Oviedo, L.Escalante, B.Ruiz, and S.Sánchez (2009).
A single residue mutation abolishes attachment of the CBM26 starch-binding domain from Lactobacillus amylovorus alpha-amylase.J Ind Microbiol Biotechnol, 36, 341-346.
18200608 O.Okhrimenko, and I.Jelesarov (2008).
A survey of the year 2006 literature on applications of isothermal titration calorimetry.J Mol Recognit, 21, 1.
17187076 A.L.van Bueren, M.Higgins, D.Wang, R.D.Burke, and A.B.Boraston (2007).
Identification and structural basis of binding to host lung glycogen by streptococcal virulence factors.Nat Struct Mol Biol, 14, 76-84.
PDB codes: 2j43 2j44
17468268 D.Guillén, M.Santiago, L.Linares, R.Pérez, J.Morlon, B.Ruiz, S.Sánchez, and R.Rodríguez-Sanoja (2007).
Alpha-amylase starch binding domains: cooperative effects of binding to starch granules of multiple tandemly arranged domains.Appl Environ Microbiol, 73, 3833-3837.
17090949 H.Watanabe, T.Nishimoto, M.Kubota, H.Chaen, and S.Fukuda (2006).
Cloning, sequencing, and expression of the genes encoding an isocyclomaltooligosaccharide glucanotransferase and an alpha-amylase from a Bacillus circulans strain.Biosci Biotechnol Biochem, 70, 2690-2702. 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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