Objective： We have continued previous work in which we demonstrated that #117 and #372 amino acids contributed to the high activities of human CYP2A13 in catalyzing 4-methylnitrosamino-1-（3-pyridyl）-1-butanone（NNK...Objective： We have continued previous work in which we demonstrated that #117 and #372 amino acids contributed to the high activities of human CYP2A13 in catalyzing 4-methylnitrosamino-1-（3-pyridyl）-1-butanone（NNK） and aflatoxin BI（AFB1） carcinogenic activation. The present study was designed to identify other potential amino acid residues that contribute to the different catalytic characteristics of two CYP2A enzymes, CYP2A6 and CYP2A13, in nicotine metabolism and provide insights of the substrate and related amino acid residues interactions. Methods： A series of reciprocally substituted mutants of CYP2A6lle^300→ Phe, CYP2A6Gly^301aAla, CYP2A6Ser^369 → Gly, CYP2A13Phe^300→ Ile, CYP2A13Ala^301 → Gly and CYP2A13Gly^369 → Set were generated by site-directed mutagenesis/baculovirus-Sf9 insect cells expression. Comparative kinetic analysis of nicotine 5＇hydroxylatin by wild type and mutant CYP2A proteins was performed. Results：All amino acid residue substitutions at 300, 301 and 369 caused significant kinetic property changes in nicotine metabolism. While CYP2A6Ile^300→ Phe and CYP2A6Gly^301→Ala mutations had notable catalytic efficiency increases compared to that for the wild type CYP2A6, CYP2A13Phe^300→Ile and CYP2A13Ala^301→Gly replacement introduced remarkable catalytic efficiency decreases. In addition, all these catalytic efficiency alterations were caused by Vmax variations rather than Km changes. Substitution of #369 residue significantly affected both Km and Vmax values. CYP2A6Ser^369 → Gly increase the catalytic efficiency via a significant Km decrease versus Vmax enhancement, while the opposite effects were seen with CYP2A13Gly^369 → Ser. Conclusion：#300, #301 and #369 residues in human CYP2A6/13 play important roles in nicotine 5＇ -oxidation. Switching #300 or #301 residues did not affect the CYP2A protein affinities toward nicotine, although these amino acids are located in the active center. Set369 to Gly substitution indirectly affected nicotine binding by creating more space and conformational flexibility for the nearby residues, such as Leu^370 which is crucial for many hydroxylations.展开更多
Lung cancer is one of the most important causes of cancer-related mortality worldwide. Human cytochrome P450 2A13 enzyme （CYP2A13） is predominantly expressed in the respiratory tract and could catalyze various carci...Lung cancer is one of the most important causes of cancer-related mortality worldwide. Human cytochrome P450 2A13 enzyme （CYP2A13） is predominantly expressed in the respiratory tract and could catalyze various carcinogens. In this study, we quantified CYP2A13 expression in non-small cell lung cancer （NSCLC） tissues and examined the relation between CYP2A13 and clinicopathologic factors. Thirty-five paired lung cancer and normal tissues were studied for the expression of the CYP2A13 gene by using real-time PCR and Western blot- ting assays. We also investigated the relationship between CYP2A13 expression and clinicopathologic factors such as age, gender, histology and lymph node status in tumor tissues. SPSS （17.0） statistical software was applied for data analysis. The real-time PCR results showed that there was no significant difference in the CYP2A13 mRNA transcript levels between tumor and paired normal tissues in the 35 samples and in 12 paired squamous cell car- cinomas. In adenocarcinoma, the expression of CYP2A13 mRNA in tumor tissues was 12.5% of that in adjacent tissues （P 〈 0.05） and it was not associated with age, gender, histology and lymph node status of the patients. The amounts of CYP2A13 proteins detected by Western blotting assays correlated well with those of the correspond- ing mRNAs. In conclusion, the expression of CYP2A13 was downregulated in lung adenocarcinoma. CYP2A13 may be involved in the development and progression of lung adenocarcinoma.展开更多
文摘Objective： We have continued previous work in which we demonstrated that #117 and #372 amino acids contributed to the high activities of human CYP2A13 in catalyzing 4-methylnitrosamino-1-（3-pyridyl）-1-butanone（NNK） and aflatoxin BI（AFB1） carcinogenic activation. The present study was designed to identify other potential amino acid residues that contribute to the different catalytic characteristics of two CYP2A enzymes, CYP2A6 and CYP2A13, in nicotine metabolism and provide insights of the substrate and related amino acid residues interactions. Methods： A series of reciprocally substituted mutants of CYP2A6lle^300→ Phe, CYP2A6Gly^301aAla, CYP2A6Ser^369 → Gly, CYP2A13Phe^300→ Ile, CYP2A13Ala^301 → Gly and CYP2A13Gly^369 → Set were generated by site-directed mutagenesis/baculovirus-Sf9 insect cells expression. Comparative kinetic analysis of nicotine 5＇hydroxylatin by wild type and mutant CYP2A proteins was performed. Results：All amino acid residue substitutions at 300, 301 and 369 caused significant kinetic property changes in nicotine metabolism. While CYP2A6Ile^300→ Phe and CYP2A6Gly^301→Ala mutations had notable catalytic efficiency increases compared to that for the wild type CYP2A6, CYP2A13Phe^300→Ile and CYP2A13Ala^301→Gly replacement introduced remarkable catalytic efficiency decreases. In addition, all these catalytic efficiency alterations were caused by Vmax variations rather than Km changes. Substitution of #369 residue significantly affected both Km and Vmax values. CYP2A6Ser^369 → Gly increase the catalytic efficiency via a significant Km decrease versus Vmax enhancement, while the opposite effects were seen with CYP2A13Gly^369 → Ser. Conclusion：#300, #301 and #369 residues in human CYP2A6/13 play important roles in nicotine 5＇ -oxidation. Switching #300 or #301 residues did not affect the CYP2A protein affinities toward nicotine, although these amino acids are located in the active center. Set369 to Gly substitution indirectly affected nicotine binding by creating more space and conformational flexibility for the nearby residues, such as Leu^370 which is crucial for many hydroxylations.
基金supported by the Project sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry (No.Z2005-2-45006)
文摘Lung cancer is one of the most important causes of cancer-related mortality worldwide. Human cytochrome P450 2A13 enzyme （CYP2A13） is predominantly expressed in the respiratory tract and could catalyze various carcinogens. In this study, we quantified CYP2A13 expression in non-small cell lung cancer （NSCLC） tissues and examined the relation between CYP2A13 and clinicopathologic factors. Thirty-five paired lung cancer and normal tissues were studied for the expression of the CYP2A13 gene by using real-time PCR and Western blot- ting assays. We also investigated the relationship between CYP2A13 expression and clinicopathologic factors such as age, gender, histology and lymph node status in tumor tissues. SPSS （17.0） statistical software was applied for data analysis. The real-time PCR results showed that there was no significant difference in the CYP2A13 mRNA transcript levels between tumor and paired normal tissues in the 35 samples and in 12 paired squamous cell car- cinomas. In adenocarcinoma, the expression of CYP2A13 mRNA in tumor tissues was 12.5% of that in adjacent tissues （P 〈 0.05） and it was not associated with age, gender, histology and lymph node status of the patients. The amounts of CYP2A13 proteins detected by Western blotting assays correlated well with those of the correspond- ing mRNAs. In conclusion, the expression of CYP2A13 was downregulated in lung adenocarcinoma. CYP2A13 may be involved in the development and progression of lung adenocarcinoma.
