Detergent-free extraction, reconstitution and characterization of membrane-anchored cytochrome-b5 in native lipids.
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ABSTRACT:
SUBMITTER: Krishnarjuna B
PROVIDER: S-EPMC7337974 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Misfolding and subsequent aggregation of endogenous proteins constitute essential steps in many human disorders, including Alzheimer and prion diseases. In most prion protein-folding studies, the posttranslational modifications, the lipid anchor in particular, were lacking. Here, we studied a fully posttranslationally modified cellular prion protein, carrying two N-glycosylations and the natural GPI anchor. We used time-resolved FTIR to study the prion protein secondary structure changes when binding to a raft-like lipid membrane via its GPI anchor. We observed that membrane anchoring above a threshold concentration induced refolding of the prion protein to intermolecular beta-sheets. Such transition is not observed in solution and is membrane specific. Excessive membrane anchoring, analyzed with molecular sensitivity, is thought to be a crucial event in the development of prion diseases.
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Project description:Membrane cytochrome b5 reductase is a pleiotropic oxidoreductase that uses primarily soluble reduced nicotinamide adenine dinucleotide (NADH) as an electron donor to reduce multiple biological acceptors localized in cellular membranes. Some of the biological acceptors of the reductase and coupled redox proteins might eventually transfer electrons to oxygen to form reactive oxygen species. Additionally, an inefficient electron transfer to redox acceptors can lead to electron uncoupling and superoxide anion formation by the reductase. Many efforts have been made to characterize the involved catalytic domains in the electron transfer from the reduced flavoprotein to its electron acceptors, such as cytochrome b5, through a detailed description of the flavin and NADH-binding sites. This information might help to understand better the processes and modifications involved in reactive oxygen formation by the cytochrome b5 reductase. Nevertheless, more than half a century since this enzyme was first purified, the one-electron transfer process toward potential electron acceptors of the reductase is still only partially understood. New advances in computational analysis of protein structures allow predicting the intramolecular protein dynamics, identifying potential functional sites, or evaluating the effects of microenvironment changes in protein structure and dynamics. We applied this approach to characterize further the roles of amino acid domains within cytochrome b5 reductase structure, part of the catalytic domain, and several sensors and structural domains involved in the interactions with cytochrome b5 and other electron acceptors. The computational analysis results allowed us to rationalize some of the available spectroscopic data regarding ligand-induced conformational changes leading to an increase in the flavin adenine dinucleotide (FAD) solvent-exposed surface, which has been previously correlated with the formation of complexes with electron acceptors.
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Project description:It has been well realized that the dependence of chemical shift anisotropy (CSA) tensors on the amino acid sequence, secondary structure, dynamics, and electrostatic interactions can be utilized in the structural and dynamic studies of proteins by NMR spectroscopy. In addition, CSA tensors could also be utilized to measure the structural interactions between proteins in a protein-protein complex. To this end, we report the experimentally measured backbone amide-(15)N CSA tensors for a membrane-bound 16.7 kDa full-length rabbit cytochrome-b5 (cytb5), in complexation with a 55.8 kDa microsomal rabbit cytochrome P450 2B4 (cytP4502B4). The (15)N-CSAs, determined using the (15)N CSA/(15)N-(1)H dipolar coupling transverse cross-correlated rates, for free cytb5 are compared with those for the cytb5 bound to cytP4502B4. An overall increase in backbone amide-(15)N transverse cross-correlated rates for the cytb5 residues in the cytb5-cytP450 complex is observed as compared to the free cytb5 residues. Due to fast spin-spin relaxation (T2) and subsequent broadening of the signals in the complex, we could measure amide-(15)N CSAs only for 48 residues of cytb5 as compared to 84 residues of free cytb5. We observed a change in (15)N CSA for most residues of cytb5 in the complex, as compared to free cytb5, suggesting a dynamic interaction between the oppositely charged surfaces of anionic cytb5 and cationic cytP450. The mean values of (15)N CSA determined for residues in helical, sheet, and turn regions of cytb5 in the complex are -184.5, -146.8, and -146.2 ppm, respectively, with an overall average value of -165.5 ppm (excluding the values from residues in more flexible termini). The measured CSA value for residues in helical conformation is slightly larger as compared to previously reported values. This may be attributed to the paramagnetic effect from Fe(III) of the heme in cytb5, which is similar to our previously reported values for the free cytb5.
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