This web page was produced as an assignment for Genetics 564 at UW-Madison in Spring 2014.
What is a small molecule assay?
Small molecule assays are often used as a starting point in drug discovery. By screening through small molecule libraries for chemical-protein interactions, it's possible to better understand how the protein functions as well.
PEX1-small molecule interactions
The most common mutation in ZS patients is a glycine-->aspartate substitution at amino acid position 843 (G843D) in the PEX1 gene. Cells with this mutation have normal transcript levels, so it's very likely that the loss of function in PEX1 generates a functional transcript that is translated to a misfolded protein that either cannot perform its intended function or is degraded by cellular machinery [1].
Treatment with generic chemical chaperones, proteins that assist with the folding of other proteins, has been shown to rescue the loss of peroxisome biogenesis and peroxisomal protein import in PEXG843D fibroblasts. Four specific compounds were found to improve PEX1 function, presumably by affecting protein folding: two protein kinase C (PKC) inhibitors, GF109203X and Ro31-8220, epicholestanol, and acacetin diacetate. Catalase and thiolase enzymes, which are important for peroxisome function, were imported more efficiently in PEXG843D fibroblasts treated with any one of these molecules. Plasmalogens are fatty acids that are a component of myelin that insulates axons, and are normally synthesized by peroxisomes. However, in PEXG843D cells, plasmalogens are not made properly. Plasmalogen synthesis can be increased in these cells by treating cells with either PKC inhibitor or acacetin diacetate, but not epicholestanol [2]. The chemical structures are shown below:
Treatment with generic chemical chaperones, proteins that assist with the folding of other proteins, has been shown to rescue the loss of peroxisome biogenesis and peroxisomal protein import in PEXG843D fibroblasts. Four specific compounds were found to improve PEX1 function, presumably by affecting protein folding: two protein kinase C (PKC) inhibitors, GF109203X and Ro31-8220, epicholestanol, and acacetin diacetate. Catalase and thiolase enzymes, which are important for peroxisome function, were imported more efficiently in PEXG843D fibroblasts treated with any one of these molecules. Plasmalogens are fatty acids that are a component of myelin that insulates axons, and are normally synthesized by peroxisomes. However, in PEXG843D cells, plasmalogens are not made properly. Plasmalogen synthesis can be increased in these cells by treating cells with either PKC inhibitor or acacetin diacetate, but not epicholestanol [2]. The chemical structures are shown below:
Discussion
The studies cited above further prove that the most common genetic cause of ZSS yields a misfolded protein product. Generic chemical chaperones that facilitate proper folding of many kinds of proteins also help to rescue PEX1 mutant phenotypes. A large-scale small molecule assay has not been conducted with regards to peroxisome biogenesis or PEX1 to date, so there are no specific chemicals known to interact with PEX1 protein.
[1] M.A. Maxwell, P.V. Nelson, S.J. Chin, B.C. Paton, W.F. Carey, D.I. Crane, A common PEX1 frameshift mutation in patients with disorders of peroxisome biogenesis correlates with severe Zellweger syndrome phenotype, Hum Genet. 105(1999) 38-44.
PMID: 10480353.
[2] R. Zhang, L. Chen, S. Jiralerspong, A. Snowden, S. Steinberg, N. Braverman, Recovery of PEX1-Gly843Asp peroxisome dysfunction by small-molecule compounds, PNAS 107(2010) 5569-5574. PMID: 20212125.
Image References
structures built with: http://www.emolecules.com/index.php
PMID: 10480353.
[2] R. Zhang, L. Chen, S. Jiralerspong, A. Snowden, S. Steinberg, N. Braverman, Recovery of PEX1-Gly843Asp peroxisome dysfunction by small-molecule compounds, PNAS 107(2010) 5569-5574. PMID: 20212125.
Image References
structures built with: http://www.emolecules.com/index.php