FIGURE 3.

Overall structure of SCL. A, a dimeric form viewed down the crystallographic 2-fold axis. The upper half of the molecules is the superimposition of one subunit in the liganded closed form onto that in the unliganded open form by least-squares fitting of Cα atoms in the large domain. The open form is pink, and the closed form is blue with a red extended lobe. The lower half of the molecule represents the other subunit in the closed form. The small domain, the large domain, and the N-terminal loop are drawn in gray, green, and orange, respectively. The coenzyme PLP and l-cysteine located in the domain interface are represented by CPK models. The extended lobe in the open form of SCL is disordered and, therefore, not shown in the model. B, superpositioning of Cα atoms of SCL onto those of cysteine desulfurases. SCL complexed with l-cysteine, human SCL, T. maritima NifS-like protein complexed with l-cysteine (PDB ID: 1ECX), and E. coli CsdB complexed with l-propargylglycine (1I29) are presented in red, orange, blue, and green, respectively. The extended lobes are shown in thick lines. The PLP moieties, bound ligands, and active site lysine and cysteine residues are represented by stick models. A part of the extended lobe of T. maritima NifS-like protein is disordered and not shown in the model.