title: Crystal structure of a periplasmic solute binding protein in metal-free, intermediate and metal-bound states from Candidatus Liberibacter asiaticus.
abstract: The Znu system, a member of ABC transporter family, is critical for survival and pathogenesis of Candidatus Liberibacter asiaticus (CLA). Two homologues of this system have been identified in CLA. Here, we report high resolution crystal structure of a periplasmic solute binding protein from second of the two gene clusters of Znu system in CLA (CLas-ZnuA2) in metal-free, intermediate and metal-bound states. CLas-ZnuA2 showed maximum sequence identity to the Mn/Fe-specific solute binding proteins (SBPs) of cluster A-I family. The overall fold of CLas-ZnuA2 is similar to the related cluster A-I family SBPs. The sequence and structure analysis revealed the unique features of CLas-ZnuA2. The comparison of CLas-ZnuA2 structure in three states showed that metal binding and release is facilitated by a large displacement along with a change in orientation of the side chain for one of the metal binding residue (His39) flipped away from metal binding site in metal-free form. The crystal structure captured in intermediate state of metal binding revealed the changes in conformation and interaction of the loop hosting His39 during the metal binding. A rigid body movement of C-domain along with partial unfolding of linker helix at its C-terminal during metal binding, as reported for PsaA, was not observed in CLas-ZnuA2. The present results suggest that despite showing maximum sequence identity to the Mn/Fe-specific SBPs, the mechanistic resemblance of CLas-ZnuA2 seems to be closer to Zn-specific SBPs of cluster A-I family.
authors: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247 667, India.
authors: Nidhi
authors: N
authors: Sharma
authors: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247 667, India.
authors: Purushotham
authors: P
authors: Selvakumar
authors: Plant Virology Laboratory, National Research Centre for Citrus, Indian Council of Agriculture Research (ICAR), Nagpur 440 010, India.
authors: Sumit
authors: S
authors: Bhose
authors: Plant Virology Laboratory, National Research Centre for Citrus, Indian Council of Agriculture Research (ICAR), Nagpur 440 010, India.
authors: Dilip Kumar
authors: DK
authors: Ghosh
authors: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247 667, India.
authors: Pravindra
authors: P
authors: Kumar
authors: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247 667, India. Electronic address: aksbsfbs@yahoo.co.in.
authors: Ashwani Kumar
authors: AK
authors: Sharma
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D008670:Metals / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019897:Periplasm / Q000378:metabolism; D033902:Periplasmic Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012230:Rhizobiaceae / Q000737:chemistry* / Q000472:pathogenicity; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D008670:Metals; D033902:Periplasmic Binding Proteins; D006639:Histidine
keywords: ABC transporters; Candidatus Liberibacter asiaticus; Crystal structure; Periplasmic solute binding protein