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Figure 3
Dual substrate-binding properties of the conserved lectin domain. (a) Strong structural conservation of the lectin domain. The 20 identical calreticulin residues are shown as sticks. The glucose-binding (GBS) and peptide-like-binding (PBS) subsite residues are highlighted in pink and yellow, respectively. (b) First example of a dual substrate-binding interaction in TcCRT, with Glc–GBS (left) and peptide-like–PBS (right) interactions. (c) Details of lectin-domain interactions with the flexible P-domain of a neighbouring molecule in EhCRT. A Cl− ion is shown in orange. (d) Simplified scheme illustrating the dual binding property of the lectin domain and how the GBS and PBS subsites can anchor interactions with glycans and peptides, respectively. (e) Global view of the large interface with the closed EhCRT conformer (dark blue), an exception among the lectin crystal-packing interactions. (f) Details of the interaction of Glc with GBS in EhCRT. (g) Superposition of Glc molecules bound in GBS in diverse contexts. The lectin-domain colour code is cyan for TcCRT, green for EhCRT and grey for HsCRT or MmCRT. The Glc colour code is salmon for EhCRT, grey for MmCRT (Kozlov et al., 2010BB24; PDB entry 3o0x) and light and dark blue for TcCRT. Several van der Waals and polar contacts are highlighted with yellow and red dashed lines, respectively.

IUCrJ
Volume 3| Part 6| November 2016| Pages 408-419
ISSN: 2052-2525
https://doi.org/10.1107/S2052252516012847