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Figure 3
The tentative active site and working mode of MltB. (a) Sequence alignment of abMltB with its structural homologs, paSltB1 and ecSlt35. Mostly conserved and partially conserved residues are colored in red and blue, respectively. Hash marks indicate conserved residues that are involved in the substrate binding. An asterisk indicates the conserved glutamic acid at the catalytic domain of MltB, which is the critical residue for enzymatic reaction. (b) Active site comparison of ecSlt35 and abMltB. Eight residues that are involved in the substrate recognition are labeled. The most critical residue directly involved in the cleavage of the substrate, Glu162 (ecSlt35)/Glu129 (abMltB), is highlighted using a red box. (c) Cartoon representation of abMltB colored according to the degree of amino-acid sequence conservation analyzed by the Consurf server. (d) Close-up view of the tentative active site shown in Consurf analysis (c), highlighting the conserved residues. Residues predicted to be involved in substrate binding are marked with black boxes, while the residue expected to play a critical role in catalysis is indicated with red box. (e) Comparison of the Ca2+-binding site of abMltB with that of paSltB1. (f) The experimental result of the ITC experiment. (g) Tentative working model of abMltB. The location of NTD–CD connecting loop is indicated.

IUCrJ
Volume 13| Part 3| May 2026| Pages 228-234
ISSN: 2052-2525
https://doi.org/10.1107/S2052252526002770