Near-stoichiometric interaction between the non-specific lipid-transfer protein of the yeast Candida tropicalis and peroxisomal acyl-coenzyme A oxidase prevents the thermal denaturation of the enzyme in vitro.
A 14-kDa peroxisomal-matrix protein, named PXP-18, of the yeast Candida tropicalis is a structural and functional homologue of the mammalian nonspecific lipid-transfer protein (identical to sterol carrier protein-2). PXP-18 protected acyl-coenzyme A oxidase (ACO), the rate limiting enzyme of the peroxisomal beta-oxidation of fatty acids, from thermal inactivation at 48 degrees C or 70 degrees C. This effect was dose-dependent and not replaceable either by chicken egg white lysozyme, which is similar to PXP-18 (insofar as it is basic, small, and monomeric), or by bovine serum albumin, a carrier of lipids in the blood. ACO was irreversibly denatured by heat treatment at 70 degrees C for 15 min. However, when ACO and PXP-18 were similarly heat-treated, they formed a large complex at a molar ratio of PXP-18 to ACO subunit that was about one, independent of their initial ratio. This near-stoichiometric complex had ACO activity after a 500-fold dilution and was accompanied by ACO that was free of PXP-18 and indistinguishable from native ACO in size and activity. PXP-18 also protected urate oxidase, another peroxisomal enzyme, from inactivation at 66 degrees C for 15 min and facilitated the renaturation of ACO denatured by 2 M urea. These results indicated that PXP-18 is active in modulating the structure of peroxisomal enzymes in vitro. It is possible that PXP-18 functions as a stress protein or as a part of the system that keeps peroxisomal proteins intact.
Niki
T
T
Faculty of Integrated Arts and Sciences, Hiroshima University, Japan.
Bun-Ya
M
M
Hiraga
Y
Y
Muro
Y
Y
Kamiryo
T
T
D042962:Acyl-CoA Oxidase; D002175:Candida / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D006358:Hot Temperature; D008830:Microbodies / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D009113:Muramidase / Q000494:pharmacology; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D011489:Protein Denaturation; D012709:Serum Albumin / Q000494:pharmacology; D014503:Urate Oxidase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014508:Urea
D005656:Fungal Proteins; D012709:Serum Albumin; C090867:POX18 protein, Candida tropicalis; D014508:Urea; D010088:Oxidoreductases; D042962:Acyl-CoA Oxidase; D014503:Urate Oxidase; D009113:Muramidase