High impact information on PEX3

• When the mutant is transfected with a good PEX3 gene, these protoperoxisomes acquire additional membrane peroxins and then import the matrix enzymes to reform peroxisomes [1].
• PEX3 functions as a PEX19 docking factor in the import of class I peroxisomal membrane proteins [2].
• Here, we show that inactivating mutations in human PEX3 cause Zellweger syndrome, abrogate peroxisome membrane synthesis, and result in reduced abundance of peroxisomal membrane proteins (PMPs) and/or mislocalization of PMPs to the mitochondria [3].
• PEX3 is the causal gene responsible for peroxisome membrane assembly-defective Zellweger syndrome of complementation group G [4].
• Expression of wild-type PEX3 in the mutant cell lines restored peroxisomal biogenesis, whereas transfection of mutated PEX3 cDNA did not [5].

Biological context of PEX3

• Interaction of PEX3 and PEX19 visualized by fluorescence resonance energy transfer (FRET) [6].
• Homozygous PEX3 mutations, each leading to C-terminal truncation of PEX3, were identified in the two patients, who both suffered from a severe Zellweger syndrome phenotype [5].
• Here we report the genomic organization, sequencing of the putative promoter region, chromosomal localization, and physical mapping of the human PEX3 gene [7].
• Pex19p was shown to interact with Pex3p in vivo, and this interaction required farnesylation of Pex19p [8].
• It is shown that insertion of a reporter protein into the peroxisomal membrane is a Pex3p-dependent process that does not require ATP/GTP hydrolysis [9].

Anatomical context of PEX3

• These results imply that Pex16p functions in peroxisome membrane assembly, more likely upstream of Pex3p [10].
• The observation of peroxisomal formation in the absence of morphologically recognizable peroxisomal membranes challenges the theory that peroxisomes arise exclusively by growth and division from preexisting peroxisomes and establishes PEX3 as a key factor in early human peroxisome synthesis [5].
• Mutation analysis of the human PEX3 gene was therefore performed in fibroblasts from patients suffering from peroxisome biogenesis disorders [7].
• The expression of a 1-16 PEX3-GFP fusion protein did not result in a peroxisomal localization, but interestingly, this and several other truncated PEX3 fusion proteins were also localized to tubular and/or vesicular structures representing mitochondria [11].
• We previously reported data on the human PEX3 cDNA and its protein, which in addition to the peroxisomal targeting sequence contains a putative endoplasmic reticulum targeting signal [7].

Associations of PEX3 with chemical compounds

• Furthermore, we find that inhibition of COPI function by brefeldin A has no effect on trafficking of PEX3 to peroxisomes and does not inhibit PEX3-mediated peroxisome biogenesis [3].

Physical interactions of PEX3

• Finally, our observation that Pex19p contains two distinct binding sites for Pex3p suggests that the peroxin may bind PMPs in multiple places and for multiple purposes [12].
• This result indicates that either one or two tryptophan residues of Pex3p (Trp-104 and Trp-224) are directly involved in binding to Pex19p [13].

Regulatory relationships of PEX3

• To address this question by fluorescence resonance energy transfer (FRET) analysis, we engineered the enhanced yellow fluorescent protein (EYFP) to the C-terminus of PEX3 and the enhanced cyan fluorescent protein (ECFP) to the N-terminus of PEX19 [14].

Other interactions of PEX3

• The observation that cells deficient in the peroxins Pex3p, Pex16p, and Pex19p lack peroxisomal membrane structures suggests that these molecules are involved in the initial stages of peroxisomal membrane formation [15].
• Functional domain mapping of peroxin Pex19p: interaction with Pex3p is essential for function and translocation [16].

Analytical, diagnostic and therapeutic context of PEX3

• Genomic PCR analysis revealed mutation of T-->G at eight bases upstream of the splicing site at the boundary of intron 10 and exon 11 of PEX3 gene, giving rise to a deletion of all of exon 11 [4].
• We created N- and C-terminal tagged PEX3 to assay its topology at the peroxisomal membrane by immunofluorescence microscopy [11].

References