title: Coexistence of two protein folding states in the crystal structure of ribosomal protein L20.
abstract: The recent finding of intrinsically unstructured proteins defies the classical structure-function paradigm. However, owing to their flexibility, intrinsically unstructured proteins generally escape detailed structural investigations. Consequently little is known about the extent of conformational disorder and its role in biological functions. Here, we present the X-ray structure of the unbound ribosomal protein L20, the long basic amino-terminal extension of which has been previously interpreted as fully disordered in the absence of RNA. This study provides the first detailed picture of two protein folding states trapped together in a crystal and indicates that unfolding occurs in discrete regions of the whole protein, corresponding mainly to RNA-binding residues. The electrostatic destabilization of the long alpha-helix and a structural communication between the two L20 domains are reminiscent of those observed in calmodulin. The detailed comparison of the two conformations observed in the crystal provides new insights into the role of unfolded extensions in ribosomal assembly.
authors.affiliation: Laboratoire de Cristallographie UPR9080, Institut de Biologie Physico-Chimique CNRS, 13, rue Pierre et Marie Curie, Paris 75005, France. timsit@ibpc.fr
authors.forename: Youri
authors.initials: Y
authors.lastname: Timsit
authors.forename: Fréderic
authors.initials: F
authors.lastname: Allemand
authors.forename: Claude
authors.initials: C
authors.lastname: Chiaruttini
authors.forename: Mathias
authors.initials: M
authors.lastname: Springer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray / Q000379:methods*; D003625:Data Collection / Q000379:methods / Q000706:statistics & numerical data; D034301:Deinococcus / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D009905:Optical Rotatory Dispersion / Q000379:methods; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012338:RNA, Ribosomal, 23S / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry; D012269:Ribosomal Proteins / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; C040045:L20 ribosomal protein, bacteria; D012338:RNA, Ribosomal, 23S; D016601:RNA-Binding Proteins; D012269:Ribosomal Proteins