title: Nuclear inelastic scattering and Mössbauer spectroscopy as local probes for ligand binding modes and electronic properties in proteins: vibrational behavior of a ferriheme center inside a β-barrel protein.
abstract: In this work, we present a study of the influence of the protein matrix on its ability to tune the binding of small ligands such as NO, cyanide (CN(-)), and histamine to the ferric heme iron center in the NO-storage and -transport protein Nitrophorin 2 (NP2) from the salivary glands of the blood-sucking insect Rhodnius prolixus. Conventional Mössbauer spectroscopy shows a diamagnetic ground state of the NP2-NO complex and Type I and II electronic ground states of the NP2-CN(-) and NP2-histamine complex, respectively. The change in the vibrational signature of the protein upon ligand binding has been monitored by Nuclear Inelastic Scattering (NIS), also called Nuclear Resonant Vibrational Spectroscopy (NRVS). The NIS data thus obtained have also been calculated by quantum mechanical (QM) density functional theory (DFT) coupled with molecular mechanics (MM) methods. The calculations presented here show that the heme ruffling in NP2 is a consequence of the interaction with the protein matrix. Structure optimizations of the heme and its ligands with DFT retain the characteristic saddling and ruffling only if the protein matrix is taken into account. Furthermore, simulations of the NIS data by QM/MM calculations suggest that the pH dependence of the binding of NO, but not of CN(-) and histamine, might be a consequence of the protonation state of the heme carboxyls.
authors.affiliation: Technische Universität Kaiserslautern, Fachbereich Physik, Erwin-Schrödinger-Str. 56, D-67663 Kaiserslautern, Germany.
authors.forename: Beate
authors.initials: B
authors.lastname: Moeser
authors.forename: Adam
authors.initials: A
authors.lastname: Janoschka
authors.forename: Juliusz A
authors.initials: JA
authors.lastname: Wolny
authors.forename: Hauke
authors.initials: H
authors.lastname: Paulsen
authors.forename: Igor
authors.initials: I
authors.lastname: Filippov
authors.forename: Robert E
authors.initials: RE
authors.lastname: Berry
authors.forename: Hongjun
authors.initials: H
authors.lastname: Zhang
authors.forename: Aleksandr I
authors.initials: AI
authors.lastname: Chumakov
authors.forename: F Ann
authors.initials: FA
authors.lastname: Walker
authors.forename: Volker
authors.initials: V
authors.lastname: Schünemann
mesh_terms: D000818:Animals; D001665:Binding Sites; D003486:Cyanides / Q000737:chemistry; D004583:Electrons; D006420:Hemeproteins / Q000737:chemistry*; D006632:Histamine / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D011789:Quantum Theory; D012239:Rhodnius; D012471:Salivary Proteins and Peptides / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer; D014732:Vibration
chemical_list: D003486:Cyanides; D006420:Hemeproteins; D008024:Ligands; D012471:Salivary Proteins and Peptides; C090560:nitrophorin; D009569:Nitric Oxide; D006632:Histamine