Molecular analysis of peroxisomal beta-oxidation enzymes in infants with Zellweger syndrome and Zellweger-like syndrome: further heterogeneity of the peroxisomal disorder

Abstract

The biosynthesis of enzymes of peroxisomal beta-oxidation was investigated in an attempt to elucidate the mechanism of deficiencies of proteins of these enzymes in 3 infants with Zellweger syndrome and in a baby with Zellweger-like syndrome with clinical and biochemical findings consistent with Zellweger syndrome except that the peroxisomes were detected electronmicroscopically. Enzyme proteins of peroxisomal beta-oxidation, acyl-CoA oxidase, bifunctional protein and 3-ketoacyl-CoA thiolase were hardly detectable, in both syndromes. Total hepatic RNA extracted from the liver of one patient with each syndrome and three controls was translated in a rabbit reticulocyte lysate protein-synthesizing system in the presence of [35S]methionine. Translatable mRNAs for all of the peroxisomal beta-oxidation enzymes were detected in both patients at much the same levels seen in the controls. Pulse labelling and chase experiments of fibroblasts from the control revealed that the 72 kDa subunit of acyl-CoA oxidase was first synthesized, after which the 52 kDa and 21 kDa subunits were processed from the 72 kDa subunit. In the patient with Zellweger syndrome, little of the 52 kDa and 21 kDa subunits of acyl-CoA oxidase were synthesized. The mature form of peroxisomal 3-ketoacyl-CoA thiolase was also not processed from its precursor form, in this patient. We consider that Zellweger-like syndrome is a new variant form of a peroxisomal disorder in which biogenesis of peroxisomes is intact, while in contrast, the biogenesis of peroxisome is considered to be defective in those with Zellweger syndrome. Multiple defects of enzymes of beta-oxidation in Zellweger-like syndrome are assumed to be caused by a defect of transport or localization of these enzymes. Our molecular analyses indicate that the enzymes of peroxisomal beta-oxidation are synthesized in patients with Zellweger and Zellweger-like syndrome but that these enzymes are not processed normally and are degraded rapidly.