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Publication Abstract from PubMed

Substrate-binding proteins (SBPs), selectively capture ligand(s) and ensure their translocation via its cognate ATP-binding cassette (ABC) import system. SBPs bind their cognate ligand(s) via an induced-fit mechanism known as the "Venus Fly-trap"; however, this mechanism lacks the atomic details of all conformational landscape as the confirmatory evidence(s) in its support. In this study, we delineate the atomic details of an SBP, beta-glucosides-binding protein (betaGlyBP) from Thermus thermophilus HB8. The protein betaGlyBP is multi-specific and binds to different types of beta-glucosides varying in their glycosidic linkages viz. beta-1,2; beta-1,3; beta-1,4 and beta-1,6 with a degree of polymerization of 2-5 glucosyl units. Structurally, the protein betaGlyBP possesses four subdomains (N1, N2, C1 and C2). The unliganded protein betaGlyBP remains in an open state, which closes upon binding to sophorose (SOP2), laminari-oligosaccharides (LAMn), cello-oligosaccharides (CELn), and gentiobiose (GEN2). This study reports, for the first time, four different structural states (open-unliganded, partial-open-unliganded, open-liganded and closed-liganded) of the protein betaGlyBP, revealing its conformational changes upon ligand binding and suggesting a two-step induced-fit mechanism. Further, results suggest that the conformational changes of N1 and C1 subdomains drive the ligand binding, unlike that of the whole N- and C-terminal domains (NTD and CTD) as known in the "Venus Fly-trap" mechanism. Additionally, profiling of stereo-selection mechanism for alpha- and beta-glucosides reveals that in the ligand-binding site four secondary structural elements (L1, H1, H2 and H3) drive the ligand selection. In summary, results demonstrate that the details of conformational changes and ligand selection are pre-encoded in the SBPs.

Conformational Trapping of a beta-Glucosides-Binding Protein Unveils the Selective Two-Step Ligand-Binding Mechanism of ABC Importers.,Chandravanshi M, Samanta R, Kanaujia SP J Mol Biol. 2020 Aug 28. pii: S0022-2836(20)30515-5. doi:, 10.1016/j.jmb.2020.08.021. PMID:32866452^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.