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Publication Abstract from PubMed

The amino acid-binding receptors, a component of ABC transporters, have evolved to cater to different specificities and functions. Of particular interest are cystine-binding receptors, which have shown broad specificity. In the present study, a putative periplasmic cystine-binding protein from Candidatus Liberibacter asiaticus (CLasTcyA) was characterized. Analysis of the CLasTcyA sequence and crystal structures in the ligand-bound state revealed novel features of CLasTcyA in comparison to related proteins. One of the unique features found in CLasTcyA structure was the positioning of the C-terminal extended loop of one chain very close to the substrate-binding site of the adjacent monomer in the asymmetric unit. The presence of a disulphide bond, unique to Candidatus Liberibacter family, holds the C-terminal extended loop in position. Analysis of the substrate-binding pocket of CLasTcyA suggested a broad specificity and a completely different orientation of the bound substrates in comparison to related protein structures. The open conformation for one of the two chains of the asymmetric unit in the Arg-bound structure revealed a limited open state (18.4 degrees ) for CLasTcyA as compared to open state of other related proteins (~ 60 degrees ). The strong interaction between Asp126 on helix-alpha5 of small domain and Arg82 (bigger domain) restricts the degree of opening in ligand-free open state. The dissociation constant of 1.26 mum by SPR and 3.7 mum by MST exhibited low affinity for the cystine. This is the first structural characterization of an l-cystine ABC transporter from plant pathogen and our results suggest that CLasTcyA may have evolved to cater to its specific needs for its survival in the host.

Crystal structures of a putative periplasmic cystine-binding protein from Candidatus Liberibacter asiaticus: insights into an adapted mechanism of ligand binding.,Kumar P, Kesari P, Kokane S, Ghosh DK, Kumar P, Sharma AK FEBS J. 2019 May 7. doi: 10.1111/febs.14921. PMID:31063259^[1]

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