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146 a.a.
_CA
Key reference
DOI no: 10.1074/jbc.M706513200 J Biol Chem 283:12415-12425 (2008) PubMed id: 18025086
Molecular basis for the selectivity and specificity of ligand recognition by the family 16 carbohydrate-binding modules from Thermoanaerobacterium polysaccharolyticum ManA. B.Bae, S.Ohene-Adjei, S.Kocherginskaya, R.I.Mackie, M.A.Spies, I.K.Cann, S.K.Nair. ABSTRACT
Enzymes that hydrolyze complex polysaccharides into simple sugars are modular in architecture and consist of single or multiple catalytic domains fused to targeting modules called carbohydrate-binding modules (CBMs). CBMs bind to their ligands with high affinity and increase the efficiency of the catalytic components by targeting the enzymes to its substrate. Here we utilized a multidisciplinary approach to characterize each of the two family 16 carbohydrate-binding domain components of the highly active mannanase from the thermophile Thermoanaerobacterium polysaccharolyticum. These represent the first crystal structures of family 16 CBMs. Calorimetric analysis showed that although these CBMs demonstrate high specificity toward beta-1,4-linked sugars, they can engage both cello- and mannopolysaccharides. To elucidate the molecular basis for this specificity and selectivity, we have determined high resolution crystal structures of each of the two CBMs, as well as of binary complexes of CBM16-1 bound to either mannopentaose or cellopentaose. These results provide detailed molecular insights into ligand recognition and yield a framework for rational engineering experiments designed to expand the natural repertoire of these targeting modules.
Selected figure(s)
Figure 2.
FIGURE 2. A, ribbon diagram of the overall structures of TpolCBM16-1 bound to the β-1,4-glucan polysaccharide substrate, cellopentaose. The protein is colored as in Fig. 1A, and the polysaccharide is shown in a ball-and-stick representation. B, surface representation of TpolCBM16-1, with the corresponding electrostatic potential, shows that the β-1,4-glucan binds in a surface cleft that is perpendicular to the orientation of the β-sheet structure.Figure 3.
FIGURE 3. A, difference Fourier electron density maps (contoured at 3over background) calculated with coefficients F[obs] - F[calc] at the ligand-binding site for the 1.2 Å resolution TpolCBM16-1-cellopentaose complex. B, direct hydrogen bonding interactions between residues of TpolCBM16-1 and cellopentaose. C, difference Fourier electron density maps (contoured at 3
The above figures are reprinted by permission from the ASBMB: J Biol Chem (2008, 283, 12415-12425) copyright 2008. Figures were selected by an automated process.
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