Protein Conformation Changes of HemAT-Bs upon Ligand Binding Probed by Ultraviolet Resonance Raman Spectroscopy

Abstract

HemAT from

Site-specific Protein Dynamics in Communication Pathway from Sensor to Signaling Domain of Oxygen Sensor Protein, HemAT-Bs

“…It is well established that the vibrational bands of Trp, Tyr, and Phe function as structural markers of proteins (16). The static UVRR studies of HemAT-Bs did not indicate any change in the hydrogen bonding interaction of any of the Tyr residues upon the binding of different ligands (28), consistent with the model of hydrogen bonding interaction between bound O 2 and Thr-95 (28).…”

“…The intensity of the Trp bands is known to be sensitive to environmental hydrophobicity and/or hydrogen bonding interactions (18,34,35). Because the hydrogen bond of Trp-132 with a nearby residue or water molecule is hardly altered by ligand binding (28), it is reasonable to conclude that the hydrophobicity around Trp-132 is changed upon CO photolysis. According to a recent time-resolved absorption and photoacoustic study of HemAT (30), volume changes occur at 50 ns after CO photolysis, suggesting an increase of the solvent-accessible area of the protein upon CO dissociation.…”

“…This is compatible with an increase of the solvent accessible area of the protein near Trp-132 at the early stage. The previous static UVRR results indicated that Trp-132 and Tyr-133 in the G-helix undergo a change in hydrophobicity upon the binding of O 2 and CO to the heme (28). In addition, the superimposition of the crystal structures of the CN-free and CN-bound forms of the sensor domain reveals that there is a noticeable alteration of the G-helix upon CN binding.…”

“…The crystal structure of the CNbound form of the truncated sensor domain suggested that Trp-132 does not form a hydrogen bond with the surrounding residues (12). However, the previous static UVRR results had suggested that Trp-132 forms a moderately strong hydrogen bond with nearby residues or water in the CO-free form, and this hydrogen bond is hardly altered upon the binding of different ligands to a reduced heme (28). Trp residues have been often used as a practical probe for helix displacement in heme proteins.…”

Internal Sense of Direction: Sensing and Signaling from Cytoplasmic Chemoreceptors

“…B. subtilis encodes one chemotaxis system with 10 chemoreceptors, 2 of which are soluble: HemAT and YfmS (62). HemAT mediates aerotaxis via oxygen binding through a coordinated heme group at its N terminus within a protoglobin domain (63). The ligand of YfmS is unknown; the sole annotated domain in this protein is the MA domain.…”