Using spectroscopic tools to probe porphyrin deformation and porphyrin-protein interactions

Abstract

The reactivity and functionality of heme proteins are to a significant extent determined by the conformation of their functional heme groups and by the interaction of axial ligands with their protein environment. This review focuses on experimental methods and theoretical concepts for elucidating symmetry lowering perturbations of the heme induced by the protein environment of the heme pocket. First, we discuss a variety of methods which can be used to probe the electric field at the heme, including spectral hole burning as well as low temperature absorption and room temperature circular dichroism spectroscopy. Second, we show how heme deformations can be described as superposition of deformations along normal coordinates, thereby using the irreducible representations of the D4h point group as a classification tool. Finally, resonance Raman spectroscopy is introduced as a tool to probe the deformations of metalloprophyrins in solution and in protein matrices by measuring and comparing intensities and depolarization properties rather than wavenumber positions.

Examination of abiotic cofactor assembly in photosynthetic biomimetics: site-specific stereoselectivity in the conjugation of a ruthenium(II) tris(bipyridine) photosensitizer to a multi-heme protein

“…6, similar to what has been reported for other hemeproteins. The optical activity of heme groups in near-UV (L band) and visual regions (B band region) of the absorption spectrum are understood to arise from the acquired chirality of the heme integrated with the asymmetrical protein environment (Blauer et al 1993;Schweitzer-Stenner 2011;Woody and Pescitelli 2014). The rotational strength of heme optical transitions is generally determined by the Coulomb interactions between the heme side chains and the protein backbone in its binding pocket (Hsu and Woody 1971).…”

Sterically induced distortions of nickel(II) porphyrins – Comprehensive investigation by DFT calculations and resonance Raman spectroscopy

“…The coexistence of planar and non-planar conformations of NiOEP [71] and (5,10,15,20-tetraphenylporphyrinato)nickel(II) [72] in solution was proven by temperature-dependent resonance Raman measurements. Furthermore, resonance Raman spectroscopy was successfully applied to probe porphyrin-protein interactions and to monitor the ligation status of heme in heme proteins [73][74][75][76]. The resonance Raman spectra of porphyrins are also highly sensitive to chemical alteration of the macrocycle.…”

Hydrogen bond donation to the heme distal ligand of Staphylococcus aureus IsdG tunes the electronic structure

“…Electronic absorption (Abs) spectroscopy has been used for over 50 years to characterize the valence electronic structure of porphyrins, including heme [31]. Circular dichroism (CD) spectroscopy has been employed more sparingly, but has proven to be an extremely sensitive probe of active site geometric structure [32,33]. Room temperature magnetic CD (MCD) spectroscopy has been extensively employed to "fingerprint" the oxidation, spin, and coordination state of heme proteins [34].…”