α-Lys424 Participates in Insertion of FeMoco to MoFe Protein and Maintains Nitrogenase Activity in Klebsiella oxytoca M5al
Conclusion
Amino Acid Residues Around FeMoco Are Immutable
FeMoco is situated deep below MoFe protein and surrounded by amino acid residues, supported by α-subunit mainly. The residues play varying roles in catalytic properties and orientation. α-Lys424 is located near homocitrate long arm. Homocitrate serves as a terminus of FeMoco. nifV− mutation, in which homocitrate was replaced by citrate resulted in significant decreases of acetylene, proton, and nitrogen reduction activity, indicating an important role of homocitrate in nitrogenase activity (Liang et al., 1990). Nitrogenase undergoes protonation during the catalytic cycle, but the specific protonation sites remain unclear (Hoffman et al., 2014). Fe2 and Fe6 atoms were considered as possible protonation sites and α-Gln190 and α-His194 residues were experimentally replaced by α-Lys190 and α-Gln194 to support the view (Zhao and Li, 2004; Guan et al., 2007). α-Lys190 substitution affected electron transfer, while α-Gln194 substitution impaired nitrogen fixation activity of nitrogenase. The α-alkoxy groups of homocitrate, functioning as bidentate ligands of Mo atom, are also possible protonation sites (Chen et al., 2014; Wang et al., 2018). α-Lys424 residue is likely involved in protonation of α-alkoxy groups. Structurally, Arg is similar to Lys, and both of them are basic amino acids. They tend to form water clusters through hydrogen bond...
Source: Frontiers in Microbiology - Category: Microbiology Source Type: research
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