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. Author manuscript; available in PMC: 2017 Sep 27.
Published in final edited form as: Biochemistry. 2016 Sep 15;55(38):5423–5433. doi: 10.1021/acs.biochem.6b00735

Figure 3.

Figure 3

Catalytic residues of Irp3 and KijD10. Stereoimages of the active sites of (A) Irp3 and (B) KijD10 highlighting the distance from the proposed catalytic residues to the substrate analogue (HPTT-COOH, pale cyan in panel A; TDP-benzene, deap teal in panel B) and NADP+ (green). In KijD10, lysine 102 is proposed to be the general acid based on mutagenesis studies.35 There is some debate among the other sugar reductases as to the general acid, but note that lysine 102 and tyrosine 186 are similar distances from the substrate analogue. In Irp3, tyrosine 128 is at a suitable distance for being the general acid whereas histidine 101, which is structurally and sequentially equivalent to lysine 102 of KijD10, is too distant to be the likely candidate.