IglG, a DUF4280-containing protein, is a structural homologue of PAAR proteins with four conserved cysteines potentially implicated in metal ion binding.

(A) Protein sequence alignment of IglG, DUF4280 (consensus sequence), FTN_0054, VcPAAR (pdb code 4JIV) and EcPAAR (4JIW). Predicted secondary structure elements of IglG are indicated above the sequence (orange rectangles for α-helices and magenta arrows for β-strands). Secondary structures of EcPAAR are indicated below the alignment in blue. Green boxes indicate the PAAR motifs, residues binding Zn in VcPAAR and EcPAAR are shaded in yellow. Conserved cysteines in the sequences of IglG, FTN_0054 and DUF4280 are shaded in red. (B) A comparison of the EcPAAR structure (blue) with homology models of DUF4280 (wheat) and IglG (magenta). Segments colored in green in the three structures correspond to the PAAR motifs. Spheres indicate the position of Zn ion (colored in yellow) in EcPAAR and the putative metal binding site in IglG. The side chains of metal binding residues are shown as ball and stick and colored in yellow (EcPAAR) or red (DUF4280 and IglG). Structures are otherwise colored as in A. (C) Profile hidden Markov model (HMM) generated by iterative searches with IglG sequence using the Jackhmmer software. The positions of the four conserved cysteine residues within IglG are indicated.