Heme-Protein Interactions and Functional Relevant Heme Deformations: The Cytochrome c Case

Transcriptomics-informed pharmacology identifies epigenetic and cell cycle regulators that enhance AAV production

Recombinant adeno-associated virus (rAAV) is a widely used viral vector for gene therapy. However, these vectors have limited availability due to manufacturing challenges with productivity and quality. These challenges can be addressed by better understanding the mechanisms that influence cellular responses during rAAV production. In this study, we aimed to identify targets that may enhance rAAV production using transcriptomic analyses of five cell lines with variable capacities for rAAV production. Using an intersectional approach, we measured the transcriptional responses of these cells during rAAV production and compared transcriptional profiles between high and base producers to identify possible targets for enhancing production. During rAAV production, we found transcriptional differences in cell cycle and nucleosome components contributed to proliferative capacity and DNA replication. We also saw upregulation of several core functions, including transcription, stress response, and Golgi and endoplasmic reticulum organization. Conversely, we saw consistent downregulation of other factors, including inhibitors of DNA-binding proteins and mitochondrial components. With a drug-connectivity analysis, we identified five classes of drugs that were predicted to enhance rAAV production. We also validated the efficacy of histone deacetylase and microtubule inhibitors. Our data uncover novel and previously identified pathways that may enhance rAAV production and quality to expand availability of rAAV for gene therapies.

Probing the versatility of cytochrome c by spectroscopic means: A Laudatio on resonance Raman spectroscopy

Over the last 50 years resonance Raman spectroscopy has become an invaluable tool for the exploration of chromophores in biological macromolecules. Among them, heme proteins and metal complexes have attracted considerable attention. This interest results from the fact that resonance Raman spectroscopy probes the vibrational dynamics of these chromophores without direct interference from the surrounding. However, the indirect influence via through-bond and through-space chromophore-protein interactions can be conveniently probed and analyzed. This review article illustrates this point by focusing on class 1 cytochrome c, a comparatively simple heme protein generally known as electron carrier in mitochondria. The article demonstrates how through selective excitation of resonance Raman active modes information about the ligation, the redox state and the spin state of the heme iron can be obtained from band positions in the Raman spectra. The investigation of intensities and depolarization ratios emerged as tools for the analysis of in-plane and out-of-plane deformations of the heme macrocycle. The article further shows how resonance Raman spectroscopy was used to characterize partially unfolded states of oxidized cytochrome c. Finally, it describes its use for exploring structural changes due to the protein's binding to anionic surfaces like cardiolipin containing membranes.

Effects of removal of the axial methionine heme ligand on the binding of S. cerevisiae iso-1 cytochrome c to cardiolipin

The cleavage of the axial S(Met) - Fe bond in cytochrome c (cytc) upon binding to cardiolipin (CL), a glycerophospholipid of the inner mitochondrial membrane, is one of the key molecular changes that impart cytc with (lipo)peroxidase activity essential to its pro-apoptotic function. In this work, UV - VIS, CD, MCD and fluorescence spectroscopies were used to address the role of the Fe - M80 bond in controlling the cytc-CL interaction, by studying the binding of the Met80Ala (M80A) variant of S. cerevisiae iso-1 cytc (ycc) to CL liposomes in comparison with the wt protein [Paradisi et al. J. Biol. Inorg. Chem. 25 (2020) 467-487]. The results show that the integrity of the six-coordinate heme center along with the distal heme site containing the Met80 ligand is a not requisite for cytc binding to CL. Indeed, deletion of the Fe - S(Met80) bond has a little impact on the mechanism of ycc-CL interaction, although it results in an increased heme accessibility to solvent and a reduced structural stability of the protein. In particular, M80A features a slightly tighter binding to CL at low CL/cytc ratios compared to wt ycc, possibly due to the lift of some constraints to the insertion of the CL acyl chains into the protein hydrophobic core. M80A binding to CL maintains the dependence on the CL-to-cytc mixing scheme displayed by the wt species.