Predominant localization of non‐specific lipid‐transfer protein of the yeast Candida tropicalis in the matrix of peroxisomes

Abstract PXP‐18 is a 14‐kDa major peroxisomal protein of the yeast Candida tropicalis and a homologue of the non‐specific lipid‐transfer protein (nsLTP) of mammals. Mammalian nsLTP is thought to facilitate the contact of membranes, to stimulate lipid‐transfer between them. If PXP‐18 functions like nsLTP, it must be present on organelle membranes. Immunoelectron microscopy of C. tropicalis cells indicated that gold particles, which visualized PXP‐18, localized exclusively in the matrix of peroxisomes. Subcellular fractionation followed by Western blotting revealed the association of PXP‐18 with peroxisomes in C. tropicalis cells. An enzyme‐linked immunosorbent assay revealed that almost all the PXP‐18 associated with peroxisomes was detectable after the solubilization of the organelle but not before, implying the predominance of PXP‐18 inside peroxisomes. This differential assay was applied to the intracellular import of the intact and truncated PXP‐18s expressed in Saccharomyces cerevisiae cells. Most of the intact PXP‐18 was shown to be imported into the matrix of host‐cell peroxisomes, whereas the truncated PXP‐18, which lacked the C‐terminal tripeptide Pro‐Lys‐Leu, no longer targeted peroxisomes. These results are consistent with the view that PXP‐18 is the matrix protein of peroxisomes and must function in a system other than that of lipid transfer.