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![[Figure 4]](jc5051fig4mag.jpg)
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Figure 4
The chitin-binding surface of CbpD. (a) Looking at the chitin-binding surface from the perspective of the crystalline substrate, equivalent residues to those identified in SmAA10 that interact with chitin (Vaaje-Kolstad, Houston et al., 2005  ; Aachmann et al., 2012; Bissaro et al., 2018) are labeled. For reference and orientation, copper is modeled into the active-site His brace as a sphere (sphere_scale 0.6) and Phe176 is labeled and shown as sticks. Residues in the putative chitin-specific L2 motif are underlined. Ser172 and Tyr40, which are phosphorylated when CbpD is expressed and secreted by P. aeruginosa (Ouidir et al., 2014), are marked with an asterisk. (b) Side view of the chitin-binding surface showing the relatively flat substrate-binding surface of the CbpD AA10 domain and the large role that the L2 region (slate) plays in substrate binding. The substrate tunnel gating pair Asn46/Glu174 are indicated with a dashed oval. (c) Based on the modeling of SmAA10 interacting with β-chitin (Bissaro et al., 2018), CbpD was manually docked onto crystalline anhydrous β-chitin (Nishiyama et al., 2011; Crystallography Open Database entry 1501776) so that the substrate-binding surface of CbpD (O and N atoms of side chains in red and blue, respectively) was parallel to the chitin surface and aligned such that the chitin runs from one end of the surface (Glu171) across the active site to the opposite end (Tyr40/Glu20). A chito-octaose (NAG8) fragment interacting with subsites −6 to +2 is shown as sticks. Subsites are numbered following the standard practice for glycoside hydrolases (Sunna et al., 1997). |
![[Figure 4]](jc5051fig4.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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