Uncovering of cytochrome P450 anatomy by SecStrAnnotator.

Protein structural families are groups of homologous proteins defined by the organization of secondary structure elements (SSEs). Nowadays, many families contain vast numbers of structures, and the SSEs can help to orient within them. Communities around specific protein families have even developed specialized SSE annotations, always assigning the same name to the equivalent SSEs in homologous proteins. A detailed analysis of the groups of equivalent SSEs provides an overview of the studied family and enriches the analysis of any particular protein at hand. We developed a workflow for the analysis of the secondary structure anatomy of a protein family. We applied this analysis to the model family of cytochromes P450 (CYPs)-a family of important biotransformation enzymes with a community-wide used SSE annotation. We report the occurrence, typical length and amino acid sequence for the equivalent SSE groups, the conservation/variability of these properties and relationship to the substrate recognition sites. We also suggest a generic residue numbering scheme for the CYP family. Comparing the bacterial and eukaryotic part of the family highlights the significant differences and reveals a well-known anomalous group of bacterial CYPs with some typically eukaryotic features. Our workflow for SSE annotation for CYP and other families can be freely used at address https://sestra.ncbr.muni.cz .

Automated Family-Wide Annotation of Secondary Structure Elements.

Secondary structure elements (SSEs) are inherent parts of protein structures, and their arrangement is characteristic for each protein family. Therefore, annotation of SSEs can facilitate orientation in the vast number of homologous structures which is now available for many protein families. It also provides a way to identify and annotate the key regions, like active sites and channels, and subsequently answer the key research questions, such as understanding of molecular function and its variability.This chapter introduces the concept of SSE annotation and describes the workflow for obtaining SSE annotation for the members of a selected protein family using program SecStrAnnotator.

MOLEonline: a web-based tool for analyzing channels, tunnels and pores (2018 update).

MOLEonline is an interactive, web-based application for the detection and characterization of channels (pores and tunnels) within biomacromolecular structures. The updated version of MOLEonline overcomes limitations of the previous version by incorporating the recently developed LiteMol Viewer visualization engine and providing a simple, fully interactive user experience. The application enables two modes of calculation: one is dedicated to the analysis of channels while the other was specifically designed for transmembrane pores. As the application can use both PDB and mmCIF formats, it can be leveraged to analyze a wide spectrum of biomacromolecular structures, e.g. stemming from NMR, X-ray and cryo-EM techniques. The tool is interconnected with other bioinformatics tools (e.g., PDBe, CSA, ChannelsDB, OPM, UniProt) to help both setup and the analysis of acquired results. MOLEonline provides unprecedented analytics for the detection and structural characterization of channels, as well as information about their numerous physicochemical features. Here we present the application of MOLEonline for structural analyses of α-hemolysin and transient receptor potential mucolipin 1 (TRMP1) pores. The MOLEonline application is freely available via the Internet at https://mole.upol.cz.

Membrane-attached mammalian cytochromes P450: An overview of the membrane's effects on structure, drug binding, and interactions with redox partners.

Mammalian cytochromes P450 are an important class of enzymes involved in the biotransformation of many endo- and exogenous compounds. Cytochrome P450 isoforms are attached to the membrane of the endoplasmic reticulum or mitochondria, and their catalytic domains move along the membrane surface while being partially immersed in the membrane environment. Their active sites are connected to both the membrane and cytosolic environments via a complex network of access channels. Consequently, they can accept substrates from both environments. The membrane also supports the interactions of cytochromes P450 with their redox partners. In this review, we provide an overview of current knowledge of the structure, flexibility, and interactions with substrates and redox partners of cytochrome P450 on membranes, amalgamating information derived from both experiments and simulations.

ChannelsDB: database of biomacromolecular tunnels and pores.

ChannelsDB (http://ncbr.muni.cz/ChannelsDB) is a database providing information about the positions, geometry and physicochemical properties of channels (pores and tunnels) found within biomacromolecular structures deposited in the Protein Data Bank. Channels were deposited from two sources; from literature using manual deposition and from a software tool automatically detecting tunnels leading to the enzymatic active sites and selected cofactors, and transmembrane pores. The database stores information about geometrical features (e.g. length and radius profile along a channel) and physicochemical properties involving polarity, hydrophobicity, hydropathy, charge and mutability. The stored data are interlinked with available UniProt annotation data mapping known mutation effects to channel-lining residues. All structures with channels are displayed in a clear interactive manner, further facilitating data manipulation and interpretation. As such, ChannelsDB provides an invaluable resource for research related to deciphering the biological function of biomacromolecular channels.

Molecular insights into the role of a distal F240A mutation that alters CYP1A1 activity towards persistent organic pollutants.

BACKGROUND: Cytochromes P450 are major drug-metabolizing enzymes involved in the biotransformation of diverse xenobiotics and endogenous chemicals. Persistent organic pollutants (POPs) are toxic hydrophobic compounds that cause serious environmental problems because of their poor degradability. This calls for rational design of enzymes capable of catalyzing their biotransformation. Cytochrome P450 1A1 isoforms catalyze the biotransformation of some POPs, and constitute good starting points for the design of biocatalysts with tailored substrate specificity. METHODS: We rationalized the activities of wild type and mutant forms of rat cytochrome P450 1A1 towards 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) and 3,3',4,4'-tetrachlorobiphenyl (PCB77) using experiments and molecular dynamics simulations. RESULTS: We showed that the enhanced activity of the CYP1A1 mutant towards TCDD was due to more efficient binding of the substrate in the active site even though the mutated site was over 2.5nm away from the catalytic center. Moreover, this mutation reduced activity towards PCB77. GENERAL SIGNIFICANCE: Amino acids that affect substrate access channels can be viable targets for rational enzyme design even if they are located far from the catalytic site.

Effect of Lipid Charge on Membrane Immersion of Cytochrome P450 3A4.

Microsomal cytochrome P450 enzymes (CYPs) are membrane-attached enzymes that play indispensable roles in biotransformations of numerous endogenous and exogenous compounds. Although recent progress in experiments and simulations has allowed many important features of CYP-membrane interactions to be deciphered, many other aspects remain underexplored. Using microsecond-long molecular dynamics simulations, we analyzed interaction of CYP3A4 with bilayers composed of lipids differing in their polar head groups, i.e., phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol. In the negatively charged lipids, CYP3A4 was immersed more deeply and was more inclined toward the membrane because of favorable electrostatic and hydrogen bonding interactions between the CYP catalytic domain and lipid polar head groups. We showed that electrostatics significantly contributes to positioning and orientation of CYP on the membrane and might contribute to the experimentally observed preferences of individual CYP isoforms to distribute in (dis)ordered membrane microdomains.

Role of Enzyme Flexibility in Ligand Access and Egress to Active Site: Bias-Exchange Metadynamics Study of 1,3,7-Trimethyluric Acid in Cytochrome P450 3A4.

Although the majority of enzymes have buried active sites, very little is known about the energetics and mechanisms associated with substrate and product channeling in and out. Gaining direct information about these processes is a challenging task both for experimental and theoretical techniques. Here, we present a methodology that enables following of a ligand during its passage to the active site of cytochrome P450 (CYP) 3A4 and mapping of the free energy associated with this process. The technique is based on a combination of a bioinformatics tool for identifying access channels and bias-exchange metadynamics and provides converged free energies in good agreement with experimental data. In addition, it identifies the energetically preferred escape routes, limiting steps, and amino acids residues lining the channel. The approach was applied to mapping of a complex channel network in a complex environment, i.e., CYP3A4 attached to a lipid bilayer mimicking an endoplasmic reticulum membrane. The results provided direct information about the energetics and conformational changes associated with the ligand channeling. The methodology can easily be adapted to study channeling through other flexible biomacromolecular channels.

The Role of Protein-Protein and Protein-Membrane Interactions on P450 Function.

This symposium summary, sponsored by the ASPET, was held at Experimental Biology 2015 on March 29, 2015, in Boston, Massachusetts. The symposium focused on: 1) the interactions of cytochrome P450s (P450s) with their redox partners; and 2) the role of the lipid membrane in their orientation and stabilization. Two presentations discussed the interactions of P450s with NADPH-P450 reductase (CPR) and cytochrome b5. First, solution nuclear magnetic resonance was used to compare the protein interactions that facilitated either the hydroxylase or lyase activities of CYP17A1. The lyase interaction was stimulated by the presence of b5 and 17α-hydroxypregnenolone, whereas the hydroxylase reaction was predominant in the absence of b5. The role of b5 was also shown in vivo by selective hepatic knockout of b5 from mice expressing CYP3A4 and CYP2D6; the lack of b5 caused a decrease in the clearance of several substrates. The role of the membrane on P450 orientation was examined using computational methods, showing that the proximal region of the P450 molecule faced the aqueous phase. The distal region, containing the substrate-access channel, was associated with the membrane. The interaction of NADPH-P450 reductase (CPR) with the membrane was also described, showing the ability of CPR to "helicopter" above the membrane. Finally, the endoplasmic reticulum (ER) was shown to be heterogeneous, having ordered membrane regions containing cholesterol and more disordered regions. Interestingly, two closely related P450s, CYP1A1 and CYP1A2, resided in different regions of the ER. The structural characteristics of their localization were examined. These studies emphasize the importance of P450 protein organization to their function.

Effect of cholesterol on the structure of membrane-attached cytochrome P450 3A4.

Cholesterol is a widely researched component of biological membranes that significantly influences membrane properties. Human cytochrome P450 3A4 (CYP3A4) is an important drug-metabolizing enzyme, wherein the catalytic domain is attached to a membrane by an N-terminal α-helical transmembrane anchor. We analyzed the behavior of CYP3A4 immersed in a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane with various amounts of cholesterol. The presence of cholesterol caused ordering and thickening of the membrane and led to greater immersion and inclination of CYP3A4 toward the membrane. Cholesterol also lowered the flexibility of and tended to concentrate around membrane-immersed parts of CYP3A4. Further, the pattern of the CYP3A4 active-site access channels was altered in the presence of cholesterol. In summary, cholesterol in the membrane affected the positioning and structural features of CYP3A4, which in turn may have implications for the activity of this enzyme in various membranes and membrane parts with different cholesterol content.

MOLE 2.0: advanced approach for analysis of biomacromolecular channels.

BACKGROUND: Channels and pores in biomacromolecules (proteins, nucleic acids and their complexes) play significant biological roles, e.g., in molecular recognition and enzyme substrate specificity. RESULTS: We present an advanced software tool entitled MOLE 2.0, which has been designed to analyze molecular channels and pores. Benchmark tests against other available software tools showed that MOLE 2.0 is by comparison quicker, more robust and more versatile. As a new feature, MOLE 2.0 estimates physicochemical properties of the identified channels, i.e., hydropathy, hydrophobicity, polarity, charge, and mutability. We also assessed the variability in physicochemical properties of eighty X-ray structures of two members of the cytochrome P450 superfamily. CONCLUSION: Estimated physicochemical properties of the identified channels in the selected biomacromolecules corresponded well with the known functions of the respective channels. Thus, the predicted physicochemical properties may provide useful information about the potential functions of identified channels. The MOLE 2.0 software is available at http://mole.chemi.muni.cz.

MOLEonline 2.0: interactive web-based analysis of biomacromolecular channels.

Biomolecular channels play important roles in many biological systems, e.g. enzymes, ribosomes and ion channels. This article introduces a web-based interactive MOLEonline 2.0 application for the analysis of access/egress paths to interior molecular voids. MOLEonline 2.0 enables platform-independent, easy-to-use and interactive analyses of (bio)macromolecular channels, tunnels and pores. Results are presented in a clear manner, making their interpretation easy. For each channel, MOLEonline displays a 3D graphical representation of the channel, its profile accompanied by a list of lining residues and also its basic physicochemical properties. The users can tune advanced parameters when performing a channel search to direct the search according to their needs. The MOLEonline 2.0 application is freely available via the Internet at http://ncbr.muni.cz/mole or http://mole.upol.cz.

Dynamics and hydration of the active sites of mammalian cytochromes P450 probed by molecular dynamics simulations.

The flexibility, active site volume, solvation, and access path dynamics of six metabolically active mammalian cytochromes P450 (human 2A6, 2C9, 2D6, 2E1, 3A4 and rabbit 2B4) are extensively studied using molecular dynamics (MD) simulations. On average, the enzymes' overall structures equilibrate on a 50+ ns timescale. The very open CYP2B4 structure closes slowly over the course of the simulation. The volumes of the active sites fluctuate by more than 50% during the MD runs; these fluctuations are mainly due to movements of the main chains, with only a handful of amino acid residues in CYP2B4, CYP2D6, CYP2A6 and CYP2C9 showing significant independent side chain movement. The volume of the active site of CYP2E1 fluctuates heavily, ranging from 220 to 1310 A(3), due to the opening and closing of gates to two adjacent cavities. CYP2E1 has the least hydrated active site of the studied CYPs; this is consistent with its preference for non-polar substrates. The CYP2A6 and CYP2E1 active sites are deeply buried, with access paths that are narrower than the radius of a water molecule. However, waters are still able to access these active sites due to local adaptations of the channel to accommodate their passage. This finding may imply that the access paths of the CYPs never fully open prior to contact with the substrate; instead, the substrate may induce adaptive conformational changes during its passage to the active site. This may also explain why some substrate recognition sites are localized along individual enzymes' access paths.