F. Musiani, E. Ippoliti, C. Micheletti, P. Carloni and S. Ciurli
Conformational fluctuations of UreG, an intrinsically disordered enzyme
Biochemistry., 2013, 52 2949–2954

Abstract
UreG are small GTP-binding (G) proteins that catalyse the hydrolysis of GTP necessary for the maturation of urease, a virulence factor in bacterial pathogenesis. UreG proteins are the first documented cases of intrinsically disordered enzymes. The comprehension of the dynamics of folding/unfolding events occurring in this protein could shed light on the enzymatic mechanism of UreG. Here, we used the recently developed replica exchange with solute tempering (REST2) computational methodology to explore the conformational space of UreG from Helicobacter pylori (HpUreG) and to identify its structural fluctuations. The same simulation and analysis protocol has been also applied to HypB from Methanocaldococcus jannaschii (MjHypB), which is closely related to UreG for both sequence and function, even though it is not intrinsically disordered. A comparison of the two systems reveals that both HpUreG and MjHypB feature a substantial rigidity of the protein regions involved in catalysis, justifying its residual catalytic activity. On the other hand, HpUreG tends to unfold more than MjHypB in portions involved in protein-protein interactions with metallo-chaperones necessary for the formation of multi-protein complexes known to be involved in urease activation.