Chen, Jia-LiangYang, YinZhang, Lin-LinLiang, HaoboHuber, ThomasSu, Xun-ChengOtting, Gottfried2018-10-182018-10-181463-9076http://hdl.handle.net/1885/148501A large number of crystal structures of bacteriophage T4 lysozyme (T4-L) have shown that it contains two subdomains, which can arrange in a compact conformation (closed state) or, in mutants of T4-L, more extended structures (open state). In solution, wild-type T4-L displays only a single set of nuclear magnetic resonance (NMR) signals, masking any conformational heterogeneity. To probe the conformational space of T4-L, we generated a site-specific lanthanide binding site by attaching 4-mercaptomethyl dipicolinic acid via a disulfide bond to Cys44 in the triple-mutant C54T/C97A/S44C of T4-L and measured pseudocontact shifts (PCS) and magnetically induced residual dipolar couplings (RDC). The data indicate that, in solution and in the absence of substrate, the structure of T4-L is on average more open than suggested by the closed conformation of the crystal structure of wild-type T4-L. A slightly improved fit was obtained by assuming a population-weighted two-state model involving an even more open conformation and the closed state, but paramagnetic relaxation enhancements measured with Gd(3+) argue against such a conformational equilibrium. The fit could not be improved by including a third conformation picked from the hundreds of crystal structures available for T4-L mutants.Financial support by the 973 program (grant 2013CB910200), the National Science Foundation of China (grants 21073101 and 21273121), and the Australian Research Council is greatly acknowledged.application/pdfhttp://www.sherpa.ac.uk/romeo/issn/1463-9076/..."author can archive post-print (ie final draft post-refereeing). 12 months embargo" from SHERPA/RoMEO site (as at 18/10/18).bacteriophage t4crystallography, x-raylanthanoid series elementsmuramidaseprotein conformationsolutionsmagnetic resonance spectroscopymodels, molecular2016-02-1710.1039/c5cp07196h