Conversion of pro-inflammatory murine Alox5 into an anti-inflammatory 15S-lipoxygenating enzyme by multiple mutations of sequence determinants

Abstract

5-Lipoxygenase (ALOX5) is a key enzyme in biosynthesis of pro-inflammatory leukotrienes whereas 15-lipoxygenases (ALOX15) have been implicated in the formation of pro-resolving eicosanoids (lipoxins, resolvins). Although mammalian LOX-isoforms share a high degree of structural similarity X-ray coordinates indicated that the substrate-binding pocket of ALOX5 is some 20% bigger than that of ALOX15 suggesting the possibility of interconverting the two isoenzymes. To test this “space-based” hypothesis we reduced the volume of the substrate-binding pocket of mouse Alox5 by introducing space-filling amino acids at critical positions and found that multiple mutations at Phe359, Ala424, Asn425 and Ala603 of Alox5 led to gradual increase in 15-HETE formation. The Phe359Trp+Ala424Ile+Asn425Met Alox5 triple mutant was a major (67±2%) 15-lipoxygenating enzyme and similar data were confirmed for human ALOX5. Structural modeling on the basis of the X-ray coordinates of ALOX5 indicated that the volume of the substrate-binding pocket inversely correlates with the share of 15-HETE biosynthesis for the human (r2=0.79, p<0.05) and the mouse (r2=0.59, p<0.01) enzyme. This data proves the principle possibility of converting pro-inflammatory 5-lipoxygenases to anti-inflammatory 15-lipoxygenases by reducing the volume of the substrate-binding pocket.