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 Title: A signal for retention of cytochrome P450 2C1 in the endoplasmic reticulum Author(s): Ahn, Kwangseog Doctoral Committee Chair(s): Kemper, Byron W. Department / Program: Molecular and Integrative Physiology Discipline: Molecular and Integrative Physiology Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Biology, Cell Biology, Animal Physiology Abstract: To determine whether the N-terminal hydrophobic sequence is also responsible for retention, the N-terminal 29 amino acids of cytochrome P450 2C1, with and without an additional 29 amino acids containing an N-glycosylation site, were fused to a soluble cytoplasmic protein, Escherichia coli $\beta$-galactosidase, or to a secreted protein, Escherichia coli alkaline phosphatase, and the hybrid proteins were expressed in COS1 cells and cellular localization was determined by subcellular fractionation, immunolocalization and the glycosylation state of the proteins. Both the $\beta$-galactosidase and alkaline phosphatase hybrid proteins were retained in the endoplasmic reticulum establishing that a specific sequence or property in the N-terminal 29 amino acids is responsible for ER retention. To further examine the possibility that retention of proteins with a large cytoplasmic domain is the default pathway, the cellular distributions of a series of P450 2C1 and EGFR chimeric proteins were examined. The data indicate that the cytoplasmic domain of the protein also has retention properties. Protein containing only the transmembrane domain of EGFR at the amino-terminus and the EGFR cytoplasmic domain were transported to the plasma membrane, while the equivalent construction with the cytoplasmic domain of cytochrome P450 was retained in the ER. The reciprocal construction with the N-terminal sequence of P450 and the cytoplasmic domain of EGFR was retained in the ER confirming the previous studies that the N-terminal sequence has ER retention properties. The retention properties of the normally N-terminal 29 amino acids was dependent on their position in the protein. We subjected the N-terminal region of P450 to extensive mutagenesis to further define the specific sequence requirements for retention. We demonstrated that the C-terminal flanking sequences following the transmembrane domain are not important for ER retention. Substitutions of either leucine or alanine for non-leucine residues did not alter the ER retention properties of the transmembrane domain. Therefore, it seems likely that another property like secondary structure, hydrophobicity, hydrophilicity, or length of the transmembrane domain of P450 may be important for ER retention. Issue Date: 1994 Type: Text Language: English URI: http://hdl.handle.net/2142/22184 Rights Information: Copyright 1994 Ahn, Kwangseog Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9503126 OCLC Identifier: (UMI)AAI9503126
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