Glyceraldehyde‐3‐phosphate dehydrogenase is a substrate of lysyl oxidase

Lysyl oxidases (LOXes) comprise a multigene family of copper‐dependent amino oxidases, that is long known to be responsible for cross‐link of collagen and elastin. In recent years, LOX has been shown to promote hypoxic metastasis. Also, LOX was found in nuclei of different cell types, and a nuclear function for LOX is still largely unknown. In search for novel LOX partners we identified several proteins that bind LOX in vitro. To do so, protein extracts from rat tissues were passed through an affinity column with immobilized recombinant LOX. The bound proteins were eluted with 7M urea and analyzed by electrophoresis and mass‐spectrometry of the eluted proteins, in comparison with a negative control. Among six differential bands, a protein with molecular weight of 36kDa was identified as glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH). Subsequently, we found that GAPDH does not significantly affect LOX activity per se but GAPDH itself is a good substrate of LOX. This might be due to the fact that GAPDH is a lysine‐rich protein with most of its lysine residues being surface‐exposed, including its unique signal of nuclear export and three lysine residues, which are necessary for nuclear import.