Mitochondrial Tryparedoxins Figure 8. Phylogenetic analysis of TXN genes of trypanosomatids showing their separation into two distinct classes. Neighbor-joining tree with bootstrapped values (500 replicates) Cf: Crithidia fasciculata; Lb: L. brazilienses; Li: L. infantum; Lm: L. major; Lmx: L. mexicana; Tb: T. brucei brucei; Tg: T. brucei gambienese; Tc: T. cruzi; Tco: T. congolense; Tv: T. vivax. doi:10.1371/journal.pone.0012607.g008 that is a defining feature of TA proteins [27]. The transmembrane domain of TA proteins determines their fate in the cell by directing and anchoring them either on the mitochondrial outer membrane, or on the membranes of the ER or of the peroxisomes (which in trypanosomatids would be the glycosomes), while leaving the entire functional N-terminal portion (which in TXNs contains the redox active domain) facing the cytosol. The subcellular localization of LiTXN3, along with its membrane topology, leave no doubts that this TXN is a TA protein (more specifically, anchored on the mitochondrial outer membrane). Again, although Trypanosoma TXN2 were not submitted to experimental scrutiny, comparison of these sequences with that of LiTXN3 strongly suggests that they are also TA members and, as such, expose their redox-active domain towards the cytosol. Since the Trypanosoma genomes do not harbor any other gene capable of coding for a fully active mitochondrial TXN, the concept that a mitochondrial TXN is not required for normal cell metabolism, unequivocally demonstrated here for Leishmania, can be extended to Trypanosoma. PLoS ONE | www.plosone.org 8 September 2010 | Volume 5 | Issue 9 | e12607