Figure 4.

Alignment of the N-terminal glycine-rich P-loop of TyrA•ACT proteins from the Class Actinobacteria. These are specific for L-arogenate as substrate, but fall into two groups with respect to the pyridine nucleotide co-substrate. The top NAD⁺-specific group possesses an aspartate (D) at position 32 (E. coli numbering), whereas the bottom NAD⁺/NADP⁺ group possesses an asparagine at the homologous position. Residue numbers are shown at the left. The species in the middle are color coded to match the hierarchical taxon positions obtained from NCBI. The variable loop of the Wierenga fingerprint [26], which in E. coli contains five residues (22–26), contains the minimal two residues in all of the Actinobacteria shown. The organisms on the right are color coded according to the taxonomic position indicated on the left (NCBI). The Rubrobacter xylanophilus TyrA_a sequence is an orphan in the tree displayed in Fig. 2, as consistent with its outlying position in the taxonomy scheme.