1HRM

THE PROXIMAL LIGAND VARIANT HIS93TYR OF HORSE HEART MYOGLOBIN

Summary for 1HRM

• Entry DOI: 10.2210/pdb1hrm/pdb
• Descriptor: MYOGLOBIN, SULFATE ION, PROTOPORPHYRIN IX CONTAINING FE, ... (4 entities in total)
• Functional Keywords: oxygen transport
• Biological source: Equus caballus (horse)
• Total number of polymer chains: 1
• Total formula weight: 17721.09

Authors

Burk, D.L.,Brayer, G.D. (deposition date: 1994-09-21, release date: 1995-01-26, Last modification date: 2024-02-07)

Primary citation

Hildebrand, D.P.,Burk, D.L.,Maurus, R.,Ferrer, J.C.,Brayer, G.D.,Mauk, A.G.
The proximal ligand variant His93Tyr of horse heart myoglobin.
Biochemistry, 34:1997-2005, 1995

PubMed Abstract: The spectroscopic and structural properties of the His93Tyr variant of horse heart myoglobin have been studied to assess the effects of replacing the proximal His residue of this protein with a tyrosyl residue as occurs in catalases from various sources. The variant in the ferric form exhibits electronic spectra that are independent of pH between pH 7 and 10, and it exhibits changes in absorption maxima and intensity that are consistent with a five-coordinate heme iron center at the active site. The EPR spectrum of the variant is that of a high-spin, rhombic system similar to that reported for bovine liver catalase. The 1D 1H-NMR spectrum of the variant confirms the five-coordinate nature of the heme iron center and exhibits a broad resonance at 112.5 ppm that is attributable to the meta protons of the phenolate ligand. This result indicates that the new Tyr ligand flips at a significant rate in this protein. The thermal stability of the Fe(III) derivative is unchanged from that of the wild-type protein (pH 8) while the midpoint reduction potential [-208 mV vs SHE (pH 8.0, 25 degrees C)] is about 250 mV lower. The three-dimensional structure of the variant determined by X-ray diffraction analysis confirms the five-coordinate nature of the heme iron center and establishes that the introduction of a proximal Tyr ligand is accommodated by a shift of the F helix (residues 88-99) in which this residue resides away from the heme pocket. Additional effects of this change are small shifts in the positions of Leu29, a heme propionate, and a heme vinyl group that are accompanied by altered hydrogen bonding interactions with the heme prosthetic group.(ABSTRACT TRUNCATED AT 250 WORDS)

PubMed: 7849057
DOI: 10.1021/bi00006a021

Experimental method

X-RAY DIFFRACTION (1.7 Å)