Intersubunit interactions associated with Tyr42 alpha stabilize the quaternary-T tetramer but are not major quaternary constraints in deoxyhemoglobin.
Previous mutational studies on Tyr42alpha variants as well as the current studies on the mutant hemoglobin alphaY42A show that the intersubunit interactions associated with Tyr42alpha significantly stabilize the alpha1beta2 interface of the quaternary-T deoxyhemoglobin tetramer. However, crystallographic studies, UV and visible resonance Raman spectroscopy, CO combination kinetic measurements, and oxygen binding measurements on alphaY42A show that the intersubunit interactions formed by Tyr42alpha have only a modest influence on the structural properties and ligand affinity of the deoxyhemoglobin tetramer. Therefore, the alpha1beta2 interface interactions associated with Tyr42alpha do not contribute significantly to the quaternary constraints that are responsible for the low oxygen affinity of deoxyhemoglobin. The slight increase in the ligand affinity of deoxy alphaY42A correlates with small, mutation-induced structural changes that perturb the environment of Trp37beta, a critical region of the quaternary-T alpha1beta2 interface that has been shown to be the major source of quaternary constraint in deoxyhemoglobin.
Kavanaugh
Jeffrey S
JS
Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, Iowa 52242, USA.
Rogers
Paul H
PH
Arnone
Arthur
A
Hui
Hilda L
HL
Wierzba
Anita
A
DeYoung
Alice
A
Kwiatkowski
Laura D
LD
Noble
Robert W
RW
Juszczak
Laura J
LJ
Peterson
Eric S
ES
Friedman
Joel M
JM
D002248:Carbon Monoxide / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000378:metabolism; D018360:Crystallography, X-Ray; D019281:Dimerization; D005914:Globins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006454:Hemoglobins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006860:Hydrogen Bonding; D007700:Kinetics; D016254:Mutagenesis, Insertional; D010100:Oxygen / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary / Q000235:genetics; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012996:Solutions; D013059:Spectrum Analysis, Raman; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism*
D003432:Cross-Linking Reagents; D006454:Hemoglobins; D021122:Protein Subunits; D012996:Solutions; D014443:Tyrosine; D002248:Carbon Monoxide; D005914:Globins; C100003:deoxyhemoglobin; D010100:Oxygen