Ts, amino acids that constitute the dimer interface are also conserved. For PNCs the sequence identity is lower, yet, critical amino acids are conserved and the overall fold is maintained in all the three domains of life. These are unifying features of nicotinamidases, even though there is a diversity of catalytic mechanisms described, with some exceptions concerning metal binding and metal ion coordination [7,20,21,29,41,42]. Homology modeling and protein-ligand docking indicates that active site residues and interactions of invertebrate NAMPTs with the substrate, nicotinamide, are similar to what is described for vertebrate NAMPTs [24,25,35?7]. In invertebrate PNCs, most interactions are maintained while additional hydrogen bonds and hydrophobic contacts were found. These new interactions might derive from complementary amino acid changes as a result ofEvolution of NAMPT and NicotinamidaseFigure 5. Structural conservation between PNC homologues. Alignment of sequences (A) and structures (B) of PNC homologues from P.horikoshii (yellow), A.baumanii (pink) and S.cerevisiae (blue). Although there is an increasing structural complexity from a monomer in Archaea, a dimer in Bacteria and an heptamer in Fungi and the amino acid identity of the sequences is around 30 , the 3D structural subunits of PNC homologues are superimposable. doi:10.1371/journal.pone.0064674.gepistatic interactions between residues [21,45], which is consistent with a structural conservation of PNCs. Our analyses validate invertebrate NAMPTs and PNCs, suggesting that both the two-step and the four-step NAD salvage pathways are functional in these organisms. These findings imply that either these enzymes are not redundant, or that specific metabolic requirements call for increased NAD production in some species that only the presence of both enzymes would fulfill.Materials and Methods Sequence analysisThe human NAMPT and the yeast PNC1 amino acid sequences were used as queries in BLAST searches [46], from National Center of Biotechnology Information, NCBI (http://www.ncbi. nlm.nih.gov/sites/genome) and Joint Genome Institute, JGI (http://genome.jgi-psf.org/) sequenced genomes. In organisms with multiple hits, the reciprocal best hit was selected for further analysis. All sequences retrieved in this process and 23148522 further analyzed are listed in Table S1. Estimates of evolutionary 4EGI-1 divergence between sequences were conducted in MEGA5 [47] and calculated as the number of amino acid substitutions per site. Analyses were conducted using the Poisson correction model [48] and involved 13 amino acid sequence homologues for eachprotein. Positions containing gaps and missing data were eliminated, resulting in a total of 436 (NAMPT) and 167 (PNC) positions in the final dataset. Alignments were visualized in Geneious [49] v5.5.6 to JI 101 cost generate logos. Structural alignments of PNC homologues were performed in Ali2D (http://toolkit. tuebingen.mpg.de/ali2d). Divergence times between species were estimated using Time Tree (http://www.timetree.org/) [50]. MATLAB version R2010b was used to generate 3D graphics (the input data is shown as Table S3) and calculate Kendall rank correlation coefficients. Correlations were measured against a reference function consisting of a monotonic increasing function of protein distances against evolutionary divergence (the hypothesis). Synteny was determined using the CHSminer software (http:// www.biosino.org/papers/CHSMiner/) [51] and the JGI genome portal (http.Ts, amino acids that constitute the dimer interface are also conserved. For PNCs the sequence identity is lower, yet, critical amino acids are conserved and the overall fold is maintained in all the three domains of life. These are unifying features of nicotinamidases, even though there is a diversity of catalytic mechanisms described, with some exceptions concerning metal binding and metal ion coordination [7,20,21,29,41,42]. Homology modeling and protein-ligand docking indicates that active site residues and interactions of invertebrate NAMPTs with the substrate, nicotinamide, are similar to what is described for vertebrate NAMPTs [24,25,35?7]. In invertebrate PNCs, most interactions are maintained while additional hydrogen bonds and hydrophobic contacts were found. These new interactions might derive from complementary amino acid changes as a result ofEvolution of NAMPT and NicotinamidaseFigure 5. Structural conservation between PNC homologues. Alignment of sequences (A) and structures (B) of PNC homologues from P.horikoshii (yellow), A.baumanii (pink) and S.cerevisiae (blue). Although there is an increasing structural complexity from a monomer in Archaea, a dimer in Bacteria and an heptamer in Fungi and the amino acid identity of the sequences is around 30 , the 3D structural subunits of PNC homologues are superimposable. doi:10.1371/journal.pone.0064674.gepistatic interactions between residues [21,45], which is consistent with a structural conservation of PNCs. Our analyses validate invertebrate NAMPTs and PNCs, suggesting that both the two-step and the four-step NAD salvage pathways are functional in these organisms. These findings imply that either these enzymes are not redundant, or that specific metabolic requirements call for increased NAD production in some species that only the presence of both enzymes would fulfill.Materials and Methods Sequence analysisThe human NAMPT and the yeast PNC1 amino acid sequences were used as queries in BLAST searches [46], from National Center of Biotechnology Information, NCBI (http://www.ncbi. nlm.nih.gov/sites/genome) and Joint Genome Institute, JGI (http://genome.jgi-psf.org/) sequenced genomes. In organisms with multiple hits, the reciprocal best hit was selected for further analysis. All sequences retrieved in this process and 23148522 further analyzed are listed in Table S1. Estimates of evolutionary divergence between sequences were conducted in MEGA5 [47] and calculated as the number of amino acid substitutions per site. Analyses were conducted using the Poisson correction model [48] and involved 13 amino acid sequence homologues for eachprotein. Positions containing gaps and missing data were eliminated, resulting in a total of 436 (NAMPT) and 167 (PNC) positions in the final dataset. Alignments were visualized in Geneious [49] v5.5.6 to generate logos. Structural alignments of PNC homologues were performed in Ali2D (http://toolkit. tuebingen.mpg.de/ali2d). Divergence times between species were estimated using Time Tree (http://www.timetree.org/) [50]. MATLAB version R2010b was used to generate 3D graphics (the input data is shown as Table S3) and calculate Kendall rank correlation coefficients. Correlations were measured against a reference function consisting of a monotonic increasing function of protein distances against evolutionary divergence (the hypothesis). Synteny was determined using the CHSminer software (http:// www.biosino.org/papers/CHSMiner/) [51] and the JGI genome portal (http.
