Role of C-terminal sequence of cytochrome P450scc in folding and functional activity

To elucidate the role of Arg472 and C-terminal sequence of the mature form of cytochrome P450scc, a mitochondrial cytochrome P450, in the present work we have performed sequential removal of the C-terminal amino acid residues of the hemeprotein and evaluated their functional role in folding and catalysis. The removal of 2, 4, 7, or 9 amino acid residues (cytochrome P450scc mutants Delta2, Delta4, Delta7, and Delta9) does not significantly affect the physicochemical properties of the truncated forms of cytochrome P450scc, but results in significant increase in the expression level of the hemeprotein in Escherichia coli (Delta4 cytochrome P450scc mutant). However, removal of 10 C-terminal amino acid residues (Delta10 cytochrome P450scc) of mature form of cytochrome P450scc (replacement of codon for Arg472 for stop-codon) is followed by loss of the ability for correct folding in E. coli. Based on these data, it is concluded that the C-terminal amino acid residues of cytochrome P450scc (DeltaArg472-Ala481) play an important role in correct recombinant protein folding and heme binding by cytochrome P450scc during its expression in E. coli, while folding of mitochondrial cytochrome P450scc during its heterologous expression in bacterial cells is more similar to the folding of prokaryotic soluble cytochrome P450's than to microsomal cytochrome P450's.     

AmylPepPred: Amyloidogenic Peptide Prediction tool

We present an efficient computational architecture designed using supervised machine learning model to predict amyloid fibril forming protein segments, named AmylPepPred. The proposed prediction model is based on bio-physio-chemical properties of primary sequences and auto-correlation function of their amino acid indices. AmylPepPred provides a user friendly web interface for the researchers to easily observe the fibril forming and non-fibril forming hexmers in a given protein sequence. We expect that this stratagem will be highly encouraging in discovering fibril forming regions in proteins thereby benefit in finding therapeutic agents that specifically aim these sequences for the inhibition and cure of amyloid illnesses.

Availability

AmylPepPred is available freely for academic use at www.zoommicro.in/amylpeppred     

Structural Basis of Human CYP51 Inhibition by Antifungal Azoles

The obligatory step in sterol biosynthesis in eukaryotes is demethylation of sterol precursors at the C14-position, which is catalyzed by CYP51 (sterol 14-alpha demethylase) in three sequential reactions. In mammals, the final product of the pathway is cholesterol, while important intermediates, meiosis-activating sterols, are produced by CYP51. Three crystal structures of human CYP51, ligand-free and complexed with antifungal drugs ketoconazole and econazole, were determined, allowing analysis of the molecular basis for functional conservation within the CYP51 family. Azole binding occurs mostly through hydrophobic interactions with conservative residues of the active site. The substantial conformational changes in the B′ helix and F-G loop regions are induced upon ligand binding, consistent with the membrane nature of the protein and its substrate. The access channel is typical for mammalian sterol-metabolizing P450 enzymes, but is different from that observed in Mycobacterium tuberculosis CYP51. Comparison of the azole-bound structures provides insight into the relative binding affinities of human and bacterial P450 enzymes to ketoconazole and fluconazole, which can be useful for the rational design of antifungal compounds and specific modulators of human CYP51.     

The cyclooxygenases

Cyclooxygenases (COXs) catalyze the rate-limiting step in the production of prostaglandins, bioactive compounds involved in processes such as fever and sensitivity to pain, and are the target of aspirin-like drugs. COX genes have been cloned from coral, tunicates and vertebrates, and in all the phyla where they are found, there are two genes encoding two COX isoenzymes; it is unclear whether these genes arose from an early single duplication event or from multiple independent duplications in evolution. The intron-exon arrangement of COX genes is completely conserved in vertebrates and mostly conserved in all species. Exon boundaries largely define the four functional domains of the encoded protein: the amino-terminal hydrophobic signal peptide, the dimerization domain, the membrane-binding domain, and the catalytic domain. The catalytic domain of each enzyme contains distinct peroxidase and cyclooxygenase active sites; COXs are classified as members of the myeloperoxidase family. All COXs are homodimers and monotopic membrane proteins (inserted into only one leaflet of the membrane), and they appear to be targeted to the lumenal membrane of the endoplasmic reticulum, where they are N-glycosylated. In mammals, the two COX genes encode a constitutive isoenzyme (COX-1) and an inducible isoenzyme (COX-2); both are of significant pharmacological importance.     

Site-Directed Mutagenesis of Cytochrome P450scc (CYP11A1). Effect of Lysine Residue Substitution on Its Structural and Functional Properties

Our previous chemical modification and cross-linking studies identified some positively charged amino acid residues of cytochrome P450scc that may be important for its interaction with adrenodoxin and for its functional activity. The present study was undertaken to further evaluate the role of these residues in the interaction of cytochrome P450scc with adrenodoxin using site-directed mutagenesis. Six cytochrome P450scc mutants containing replacements of the surface-exposed positively charged residues (Lys103Gln, Lys110Gln, Lys145Gln, Lys394Gln, Lys403Gln, and Lys405Gln) were expressed in E. coli cells, purified as a substrate-bound high-spin form, and characterized as compared to the wild-type protein. The replacement of the surface Lys residues does not dramatically change the protein folding or the heme pocket environment as judged from limited proteolysis and spectral studies of the cytochrome P450 mutants. The replacement of Lys in the N-terminal sequence of P450scc does not dramatically affect the activity of the heme protein. However, mutant Lys405Gln revealed rather dramatic loss of cholesterol side-chain cleavage activity, efficiency of enzymatic reduction in a reconstituted system, and apparent dissociation constant for adrenodoxin binding. The present results, together with previous findings, suggest that the changes in functional activity of mutant Lys405Gln may reflect the direct participation of this amino acid residue in the electrostatic interaction of cytochrome P450scc with its physiological partner, adrenodoxin.     

Probing the interaction of bovine cytochrome P450scc (CYP11A1) with adrenodoxin: evaluating site-directed mutations by molecular modeling

The present study was undertaken to evaluate the role of positively charged amino acid residues proposed to reside on the proximal surface of bovine cytochrome P450 cholesterol side chain cleavage (P450scc, CYP11A1) and to determine which residues may be involved in protein-protein interactions with the electron carrier adrenodoxin (Adx). In previous studies, nine different lysine residues were identified by chemical and immunological cross-linking experiments as potentially interacting with Adx, while in the present study, two arginine residues have been identified from sequence alignments. From these 11 residues, 13 different P450scc mutants were made of which only seven were able to be expressed and characterized. Each of the seven mutants were evaluated for their ability to bind Adx, to be reduced, and for their enzymatic activity. Among these, K403Q and K405Q showed a consistent decrease in Adx binding, the ability to be reduced by Adx, and enzymatic activity, with K405Q being affected to a much greater extent. More dramatic was the complete loss of Adx binding by R426Q, while still retaining its ability to be chemically reduced and bind carbon monoxide. Independently, a homology model of P450scc was constructed and docked with the structure of Adx. Four potential sites of interaction were identified: P450scc:K403 with Adx:D76, P450scc:K405 with Adx:D72; P450scc:R426 with Adx:E73, and P450scc:K267 with Adx:E47. Thus, the biochemical and molecular modeling studies together support the hypothesis that K267, K403, K405, and R426 participate in the electrostatic interaction of P450scc with Adx.     

'Navius' kissing stents for coronary bifurcation stenosis,recreating a new metallic carina: an IVUS-assessed case report

We report a case of implantation of a new design of stent which allows creation of a double-hemispheric lumen for the treatment of a bifurcational stenosis. The unfavourable outcome following the implantation of this stent is described.     

Conformational dynamics and molecular interaction reactions of recombinant cytochrome p450scc (CYP11A1) detected by fluorescence energy transfer.

Bovine adrenocortical cytochrome P450scc (P450scc) was expressed in Escherichia coli and purified as the substrate bound, high-spin complex (16.7 nmol of heme per mg of protein, expression level in E. coli about 400-700 nmol/l). The recombinant protein was characterized by comparison with native P450scc purified from adrenal cortex mitochondria. To study the interaction of the electron transfer proteins during the functioning of the heme protein, recombinant P450scc was selectively modified with fluorescein isothiocyanate (FITC). The present paper shows that modified P450scc, purified by affinity chromatography using adrenodoxin-Sepharose to remove non-covalently bound FITC, retains the functional activity of the unmodified enzyme, including its ability to bind adrenodoxin. Based on the efficiency of resonance fluorescence energy transfer in the donor-acceptor pair, FITC-heme, we calculated the distance between Lys(338), selectively labeled with the dye, and the heme of P450scc. The intensity of fluorescence from the label dramatically changes during: (a) denaturation of P450scc; (b) changing the spin state or redox potential of the heme protein; (c) formation of the carbon monoxide complex of reduced P450scc; (d) as well as during reactions of intermolecular interactions, such as changes of the state of aggregation, complex formation with the substrate, binding to the electron transfer partner adrenodoxin, or insertion of the protein into an artificial phospholipid membrane. Selective chemical modification of P450scc with FITC proved to be a very useful method to study the dynamics of conformational changes of the recombinant heme protein. The data obtained indicate that functionally important conformational changes of P450scc are large-scale ones, i.e. they are not limited only to changes in the dynamics of the protein active center. The results of the present study also indicate that chemical modification of Lys(338) of bovine adrenocortical P450scc does not dramatically alter the activity of the heme protein, but does result in a decrease of protein stability.     

Biosynthesis of chlorophyll P-680 of photosystem II in greening leaves of plants adapted to heat shock

In etiolated pea and maize leaves illuminated after incubation at 38 degreesC, a new dark reaction was shown manifested in the bathochromic shift of spectral bands and accompanied by esterification of the product of protochlorophyllide photochemical reduction--Chld 684/676: Chld 684/676 --> Chl 688/680. After completion of the reaction a rapid (20-30 sec) quenching of the fluorescence of the reaction product (Chl 688/680) was observed. The reaction Chld 684/676 --> Chl 688/680 is inhibited under anaerobic conditions and in the presence of cyanide; the reaction accompanied by Chl 688/680 fluorescence quenching is not observed in pea mutants with impaired function of photosystem II reaction centers. The spectral properties of the formed Chl form with the absorption maximum at 680 nm, fluorescence quenching, and simultaneous synthesis of pheophytin suggest that the reaction is connected with the chlorophyll of photosystem II reaction center--P-680.