Towards the molecular mechanism of action of human renalase on the cardiovascular system

INTRODUCTION: Within a post-genomic survey of human genes encoding soluble, potentially secreted proteins of unknown function, a putative enzyme carrying a FAD-binding signature was identified (1). This protein, which displays low similarity to flavin-containing monoamine oxidases (MAOs) was named renalase, since it is preferentially synthesized in the kidney (1). It has been proposed to be secreted into the bloodstream, where it was shown to modulate blood pressure and heart rate (1, 2). It was hypothesized that renalase could represent a novel type of MAO, acting on circulating catecholamines (1, 3). Thus, renalase may be a novel key participant in the interplay between the excretory and circulating systems. Low blood renalase level in patients suffering from chronic kidney disease might be responsible for the increased risk of cardiovascular complications in these subjects (4). With the aim to clarify the mechanism of action of human renalase at the molecular level, we have undertaken the purification and characterization of the protein produced in Escherichia coli. RESULTS: Recombinant human renalase has been produced in E. coli as a FAD-containing soluble protein and purified (5), allowing the determination of its biochemical properties, which unexpectedly were markedly different from those of mammalian MAOs. The protein is a monomer containing no disulfide bridge. The cofactor is firmly, but not covalently bound to the apoprotein and its reactivity towards different compounds is at variance with those of MAOs. Finally, recombinant renalase was found to be devoid of any oxidase activity towards various biogenic amines. On the contrary, we found experimental evidence that renalase could catalyze reactions different from oxidative deamination. We conclude that the previous proposal that renalase is a novel MAO isoform should be rejected. 1. Xu J. et al. (2005) J. Clin. Invest. 115, 1275-1280 2. Li, G. et al. (2008) Circulation 117, 1277-1282 3. Wang J. et al. (2008) Mol. Biol. Rep. 35, 613-620 4. Desir G. V. (2009) Kidney Int. 76, 366-370 5. Pandini V. et al. (2010) Protein Expr Purif. doi:10.1016/j.pep.2010.03.008