FIGURE 1.

Crystal packing of Vp-MtlR monomers and Vp-MtlR dimer. A, the four Vp-MtlR monomers in one asymmetric unit. The monomers A and B form a dimer, and monomers C and D form a dimer. Both dimers are of 2-fold pseudosymmetry. For clarity, only the front helices of the AB-dimer are labeled. The AB-dimer and CD-dimer form extensive interactions across their interface and potentially form a tetramer, as discussed under “MtlR and YggD Dimers and Tetramers.” B, a ribbon drawing of a Vp-MtlR dimer (AB-dimer). The orientation of the dimer is related to its position in A by a rotation about 90° around the horizontal axis. All helices of the novel layered α-helical fold are labeled. The α8 helix is missing in Vp-MtlR in comparison with the structure of Sf-YggD shown in Fig. 2. This figure and other ribbon diagram figures were prepared using the program PyMOL (available on the World Wide Web).