You may not have heard of the cytochrome P450 superfamily of enzymes, but these proteins are essential to humans through the metabolic processing of drugs, pesticides, fatty acids, fat-soluble vitamins, chemical carcinogens, and the biosynthesis of essential steroids. plays diverse and important roles in the body. Contains sterols.

Sterols are a family of compounds that share a central ring structure and are important for the life of numerous organisms. The most well-known sterol in humans is cholesterol. Cholesterol is an important component of cell membranes and is something doctors keep in mind, given that elevated blood cholesterol levels can increase the risk of cardiovascular disease.

fred gengerich

laboratory fred gengerich, Dr. Tadashi Inagami. The biochemistry professor has been studying cytochrome P450 for his 50 years. In a new paper published in applied chemistry In January 2024, the Gengerich lab discovered the mechanism used by cytochrome P450 51 (a P450 enzyme present in all families of life) to catalyze a key three-step reaction in sterol biosynthesis: the metabolism of lanosterol. investigated.

“This is a challenging but rewarding project that provides the first clear answer to a long-standing and controversial mechanistic question in eukaryotic sterol biosynthesis,” said lead author and biochemistry graduate student he said. Kevin McCarty.

The catalytic cycle of all P450 enzymes involves the formation of two active heme iron species, compound 0 and compound I (the latter naturally formed from compound 0), which are required for P450-catalyzed reactions, including lanosterol metabolism. . Although the role of Compound I in the first two steps of lanosterol metabolism is well established, conflicting data from different laboratories suggest that P450 51 uses Compound 0 to accomplish the critical final step. Scientists remain unclear whether to use compound I or compound I.

By using advanced analytical techniques first refined by former Guengerich postdoctoral fellow Francis Yoshimoto The study tracked the incorporation of an oxygen isotope called 18O into the products of the P450 reaction, and McCarty and colleagues found that both Compound 0 and Compound I play active chemical roles in the final steps of lanosterol metabolism. This is the first time we have shown that it is possible.

Cytochrome P450s are a superfamily of heme-containing enzymes that catalyze a variety of oxidation reactions. Shown here is the cytochrome P450 CYP19A1 complexed with testosterone. CYP19A1 is involved in hormone synthesis and degradation.

Indeed, the results shown in applied chemistry According to the paper, compound 0 is the major heme species responsible for the final step of human P450 51 catalysis (approximately 85% of the reaction), while compound I still plays a quantifiable minor role (approximately 14% of the reaction). ) has been shown to play a role.

collaboration with Galina RepeshevaThe researchers, a research professor of biochemistry, compared the relative contributions of each heme species in four P450 51 enzymes in pathogenic yeasts, amoebas, and trypanosomes, a type of parasite, to their human orthologs. Although yeast and amoeba enzymes showed similar results to human proteins, results from trypanosomal enzymes revealed interesting mechanistic differences. That is, compound 0 and compound I shared approximately equal contributions to the reaction.

These results add depth to our collective and mechanistic understanding of P450 enzymes, particularly those involved in sterol biosynthesis.

“This involved a 17-step chemical synthesis, five different purified P450 51 enzymes from my collaborator Professor Galina Repesheva, careful attention to the use of an oxygen atmosphere in the reaction, advanced high-resolution mass spectrometry, and my own “This is a careful study by all the authors in our lab,” Guengerich said. He says his team’s “attention to detail” allowed them to “decipher this system” and provide a clear analysis of the branching enzyme machinery.

“Our findings represent an important advance in understanding the function of P450 51 in humans and a variety of pathogens, and we hope this will aid in the continued research of drugs that target P450 51,” said McCarty. the professor said.

Currently, many existing antifungal drugs inhibit fungal P450 51 enzymes, interfering with the ability of microorganisms to produce essential sterols and reproduce. However, resistance to antifungal drugs, coupled with the existence of life-threatening fungal infections for which there is no cure, highlights the continued need for novel P450 51 -targeting agents.

In the future, the Gengerich and Repesheva laboratories plan to further analyze the amoeba-derived P450 51 enzyme to explore its mechanistic specificity that could be used as a potential drug target.

This article originally appeared on the Basic Science page of the Vanderbilt University School of Medicine website. Please read the original text here.