Abstract:
:The cytochrome P-450 superfamily of enzymes catalyzes the oxidative metabolism of innumerable lipophilic compounds (e.g., drugs, carcinogens, steroids). Although the three-dimensional structure of a soluble bacterial P-450 (P-450cam) has been solved, little is known about the structures of the membrane-bound mammalian P-450s. Thus, the structural features of these enzymes that determine their multisubstrate specificity are unknown. In this report, we identify a segment of the primary structure of the structurally similar but functionally distinct cytochromes P-450IIC5 and P-450IIC4, which determines the apparent affinity of these cytochromes for the conversion of progesterone into the mineralocorticoid deoxycorticosterone. P-450IIC5 exhibits a greater than 10-fold lower apparent Km than P-450IIC4 for progesterone 21-hydroxylation. Chimeric cDNAs were constructed and expressed in COS-1 cells, which encode hybrids between these enzymes. The hybrid enzymes were assayed for catalytic activity and compared to the parental proteins. A segment of P-450IIC5 was identified that conferred the lower Km of P-450IIC5 to P-450IIC4. Sequential reduction of the length of the exchanged segments led to a hybrid enzyme with a high affinity derived largely from P-450IIC4, which contains three amino acid residues derived from P-450IIC5 clustered between positions 113 and 118. This suggests that this region is part of a substrate binding domain. This region maps by alignment of amino acid sequences to a residue of P-450cam, which has been implicated in substrate binding, suggesting that these segments of the primary structure serve a similar functional role in these two distantly related proteins.
journal_name
Proc Natl Acad Sci U S Aauthors
Kronbach T,Larabee TM,Johnson EFdoi
10.1073/pnas.86.21.8262subject
Has Abstractpub_date
1989-11-01 00:00:00pages
8262-5issue
21eissn
0027-8424issn
1091-6490journal_volume
86pub_type
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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doi:10.1073/pnas.93.23.12861
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
pub_type: 杂志文章
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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更新日期:1995-08-15 00:00:00
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更新日期:2015-01-06 00:00:00