Human Renin-Binding Protein Is the Enzyme N-Acetyl-D-Glucosamine 2-Epimerase

Abstract

The existence of human renin-binding protein (RnBP) in the kidney has been shown by the isolation and characterization of a complex of porcine renin-human RnBP [S. Takahashi et al. (1985) J. Biochem. 97, 671-677]. However, the properties of the free form of human RnBP had not been understood, because of the limitation of materials. In the present study, we have expressed human RnBP in Escherichia coli JM 109 cells under the transcriptional control of taq promoter and purified it by conventional column chromatographies. The purified recombinant human RnBP (rhRnBP) exists as a dimer and inhibits porcine renin activity through formation of a complex of porcine renin with rhRnBP, the so-called highmolecular-weight renin. Moreover, the rhRnBP catalyzes the interconversion between N-acetyl-D-glucosamine (GIcNAc) and N-acetyl-D-Mannosamine (ManNAc) with the apparent K_m values of 21.3mM for GlcNAc and 12.8mM for ManNAc, and 0.13mM for effector ATP. ATP is essential for the GlcNAc 2-epimerase activity of human RnBP. These results indicate that the human RnBP is a GIcNAc 2-epimerase.