title: Insights in the (un)structural organization of Bacillus pasteurii UreG, an intrinsically disordered GTPase enzyme.
abstract: In the past, enzymatic activity has always been expected to be dependent on overall protein rigidity, necessary for substrate recognition and optimal orientation. However, increasing evidence is now accumulating, revealing that some proteins characterized by intrinsic disorder are actually able to perform catalysis. Among them, the only known natural intrinsically disordered enzyme is UreG, a GTPase that, in plants and bacteria, is involved in the protein interaction network leading to Ni(2+) ions delivery into the active site of urease. In this paper, we report a detailed analysis of the unfolding behaviour of UreG from Bacillus pasteurii (BpUreG), following its thermal and chemical denaturation with a combination of fluorescence spectroscopy, calorimetry, CD and NMR. The results demonstrate that BpUreG exists as an ensemble of inter-converting conformations, whose degrees of secondary structure depend on temperature and denaturant concentration. In particular, three major types of conformational ensembles with different degrees of residual structure were identified, with major structural characteristics resembling those of a molten globule (low temperature, absence of denaturant), pre-molten globule (high temperature, absence or presence of denaturant) and random coil (low temperature, presence of denaturant). Transitions among these ensembles of conformational states occur non-cooperatively although reversibly, with a gradual loss or acquisition of residual structure depending on the conditions. A possible role of disorder in the biological function of UreG is envisaged and discussed.
authors.affiliation: Laboratory of Bioinorganic Chemistry, University of Bologna, Bologna, Italy. barbara.zambelli@unibo.it
authors.forename: Barbara
authors.initials: B
authors.lastname: Zambelli
authors.forename: Nunilo
authors.initials: N
authors.lastname: Cremades
authors.forename: Paolo
authors.initials: P
authors.lastname: Neyroz
authors.forename: Paola
authors.initials: P
authors.lastname: Turano
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Uversky
authors.forename: Stefano
authors.initials: S
authors.lastname: Ciurli
mesh_terms: D001407:Bacillus / Q000187:drug effects / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000378:metabolism*; D019791:Guanidine / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D028044:Phosphate-Binding Proteins; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D028044:Phosphate-Binding Proteins; C082270:ureG protein, Bacteria; D020558:GTP Phosphohydrolases; D019791:Guanidine