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The BGJ398 results obtained from the primary structures led us to study the theoretical physico-chemical properties of these new proteins (Table 2). The physico-chemical data showed that bacterial NrlA and fungal Frm2/Hbn1 proteins have an acidic pI (average pI of 6.08 and 6,44, respectively). The polypeptide chains lengths vary from 190 to 233 aa [molecular weight (M.W.) from 21.21 to 25.43 kDa; Table 2] for bacterial NrlAp, while the fungal Frm2p/Hbn1p sequences showed polypeptide chains in the range of 193–242 aa (M.W. from 20.74 to 27.07 kDa; Table 2).
HCA and three-dimensional protein modeling of nitroreductase-like sequences
An HCA comparison between bacterial NrlAp (SmuNrlAp and LcaNrlAp, respectively; Table 1) and fungal Frm2/Hbn1 proteins (SceFrm2p, SceHbn1p, and MgrFrm2p, respectively; Table 1) indicated a high degree of similarity of secondary structures among the proteins, being composed in a greater extent by α-helices (α1–α8; Fig. 2). Two subdomains (subdomains 1 and 2; Fig. 2) separated by a hinge region ( Fig. 2) could be clearly indentified in all proteins analysed. Both subdomains 1 and 2 show an average similarity score of 68% and 63%, respectively. In addition, the Frm2p sequence of Magnaporthea grisea (MgrFrm2p; Table 1) contains a signal peptide for mitochondrial location ( Fig. 2), indicating a possible role of MgrFrm2p within this organelle. We could not identify mitochondrial targeting sequences in the yeast Frm2p/Hbn1p, but experimental data from our laboratory shows that yeast cells defective for Frm2p and/or Hbn1p have a high induction of petite colonies (data not shown).