Phylogenetic analysis of chromate transport (CHR) protein family

The ChrA protein is encoded in a Pseudomonas aeruginosa plasmid and it confers resistance to the toxic ion chromate through the chromate efflux from the cytoplasm. In the protein databases ChrA is a member of the CHR family, composed of at least 135 members, distributed in the three domains of life. The aim of this work was to make a phylogenetic analysis of the CHR family. A Psi‐Blast exhaustive search for ChrA homologous proteins was done at the NCBI database. We obtained 135 sequences homologous to ChrA from P. aeruginosa: 77 long‐chain sequences, or bidomain (LCHR), and 58 short‐chain sequences, or monodomain (SCHR). LCHR sequences were cut in the amino and carboxyl domains and the resultant domains were aligned whit the SCHR proteins. A phylogenetic tree was reconstructed applying four different methods, obtaining very similar results. The domains were grouped in three clusters: the SCHR proteins cluster, the amino domain cluster of LCHR proteins and the carboxyl domain cluster of CHR proteins. The separate distribution of the LCHR and SCHR proteins, and the fact that chromate transport has been demonstrated only in LCHR proteins, suggests that the SCHR proteins form a parologous group in the CHR family. In addition, we found evidence suggesting an ancient origin of LCHR proteins from the fusion of two SCHR protein encoding genes. Supported by CONACYT‐México 41712Q, 45003M, CIC (U‐Michoacana), and DGAPA‐UNAM IN224206 ‐2