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. 2010 Aug 4;285(41):31603–31615. doi: 10.1074/jbc.M110.149310

FIGURE 4.

FIGURE 4.

The dynamic loops for chitin binding. A, the electrostatic molecular surface of ChiNCTU2 is shown in gray with the dynamic loop (Ile-106–Val-112) shown in red and green colors for native and mutant E145G/Y227F+(NAG)4 complex structures, respectively, after superimposition. Upon the substrate binding, the loop moved from the native open form (red) to the binding close form (green). B, shown is a close view of the chitin-binding mode. The native (in red sticks) and E145G/Y227F+(NAG)4 (in green sticks) structures show that the side chain of Glu-68 and Gln-109 alters its position ∼4.0 Å (about the length of the monosaccharide) and 4.6 Å, respectively, to interact with chitin in the active site. The swing of the dynamic loop (Ile-106–Val-112) between the native and complex structure allows Gln-109 to swing over the −2-(NAG). The two dynamic loops in the structure of D143A+(NAG)2 (blue) are in the position similar to the native open form (pre-catalyzing-stage position). The structure of D143A+(NAG)2 also showed the main chain of catalytic residue Glu-145 relocated its position (blue). The side chain of Phe43 is fixed among three structures and positioned close to the potential −3 subsite. C, shown is a scheme of (NAG)4 and residue Gln-109 (red, native open form; green, binding close form). The boat-form −1-(NAG) shifts the linear +1 and +2-(NAG) from the horizontal (gray) to the vertical (black) position, which shortens the distance between −2 and +1 to the distance corresponding to a mono-(NAG) moiety (∼4.6 A) related to Gln-109.