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Conformational and functional significance of the α140 side‐chain in HbA: a UV and visible resonance Raman study of three α140 mutants
Author(s) -
Juszczak Laura,
Samuni Uri,
Friedman Joel M.
Publication year - 2005
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1322
Subject(s) - chemistry , raman spectroscopy , resonance (particle physics) , allosteric regulation , stereochemistry , mutant , crystallography , hydrogen bond , resonance raman spectroscopy , histidine , amino acid , molecule , biochemistry , organic chemistry , enzyme , physics , optics , gene , particle physics
Continuous wave UV resonance Raman (UVRR) and nanosecond time‐resolved visible resonance Raman spectra were generated from the deoxy and CO derivatives of three α‐chain mutants of human adult hemoglobin (HbA): Yα140F, Yα140G and Yα140A. The UVRR results show that an aromatic side‐chain in the α140 site is needed for achieving the wild‐type tertiary conformation in the allosterically important α 1 β 2 interface for both the deoxy T state and the liganded R state. The wavenumbers of ν(Fe–His), the iron‐proximal histidine stretching mode, seen in the VRR spectra from the deoxy derivatives show that the hydrogen bond between α140 tyrosine and the carbonyl of α93 valine is necessary to obtain the full quaternary constraint associated with the deoxy T state even when the α 1 β 2 interface is seemingly intact. A model is presented that describes the relationship between the packing of a cluster of residues linked to both Wβ37 and Yα140 and the extent of proximal strain/quaternary constraint at the α‐chain heme. The visible resonance Raman (VRR) spectra of the 8 ns photoproduct of the CO derivatives of the three mutants in the presence and absence of allosteric effectors show that all three mutants can access the R state but they show enhanced sensitivity to added IHP. The CO derivative of the Hb(Yα140F) mutant in the presence of IHP exhibits properties consistent with the high‐affinity T state observed both for non‐equilibrium populations of HbA isolated using sol–gel matrices and for β37 mutants where the hinge region of the α 1 β 2 interface is disrupted. Copyright © 2005 John Wiley & Sons, Ltd.