The structure of this domain is known and is similar to the periplasmic binding proteins [1]. This domain binds a variety of ligands that caries in size and structure, such as amino acids, sugar phosphates, organic acids, metal cations, flavonoids, C6-ring carboxylic acids, H2O2, HOCl, homocysteine, NADPH, ATP, sulphate, muropeptides, acetate, salicylate, citrate, phenol- and quinolone derivatives, acetylserines, fatty acid CoA, shikimate, chorismate, homocysteine, indole-3-acetic acid, Na(I), c-di-GMP, ppGpp and hydrogen peroxide (Matilla et. al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: The structure of the cofactor-binding fragment of the LysR family member, CysB: a familiar fold with a surprising subunit arrangement. Tyrrell R, Verschueren KH, Dodson EJ, Murshudov GN, Addy C, Wilkinson AJ; Structure 1997;5:1017-1032. PMID:9309218