MoeB-MoaD complex

Fig. 3.4. Structure of the MoaD-MoeB complex. (A) Overall structure of the hetero-tetramer. MoaD subunits are shown in yellow, MoeB subunits in red and light blue. The twofold axis of symmetry is running vertically in the plane of the paper. The AMP is shown in...

Following the formation of the acyl adenylate the reactions will proceed along different paths. In the MoaD-MoeB complex a thiocarboxylate will be formed and the current knowledge regarding this step has been summarized (Section 3.3.5.). 

Fig. 3.7. Adenylation reaction. (A) Stereo representation of a superposition of the MoaD-MoeB complex in its apo-state (red), in complex with ATP (yellow) and after formation of the acyl adenylate (blue). (B) Proposed reaction scheme for the formation of the acyl adenylate. Arg refers to the second arginine originating either from the second subunit in case of MoeB and hetereodimeric El enzymes,...

Figure 19 The MPT synthase reaction. Precursor Z (52) is converted into MPT (53) by the transfer of two sulfur groups from the C-terminal thiocarbocylate of the MoaD subunit of MPT synthase. For the regeneration of the sulfur on MoaD, a complex is formed with MoeB. ATP consumption yields adenylated MoaD. MoaD-AMP is susceptible to sulfuration by a protein-bound persulfide group from a sulfur transferase. After the formation of the thiocarboxylate group, MoaD dissociates from the MoeB-dimer and associates with MoaE. Initial attack by the first MoaD thiocarboxylate could occur at either the Cl or C2 position of precursor Z to produce a hemisulfurated precursor Z intermediate (58).

The crystal structure of the MoeB-MoaD complex (Figure 3.4) was determined by multiple isomorphous replacement in its apo-state at 1.7-A resolution, with bound ATP at 2.9-A resolution and after formation of the covalent MoaD-adenylate at 2.1-A resolution [38]. The latter two structures were obtained by soaking either ATP or Mg-ATP into crystals of the apo-complex. 

Lake, M. W., Wuebbens, M. M., Rajagopalan, K. V., and Sghindelin, H. Mechanism of ubiquitin activation revealed by the structure of a bacterial MoeB-MoaD complex. Nature 2001, 434, 325-329. 

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