Hb Santa Clara (beta 97His-->Asn), a human haemoglobin variant: functional characterization and structure modelling.
This study examines the functional and structural effects of amino acid substitution at alpha(1)beta(2) interface of Hb Santa Clara (beta 97His-->Asn). We have characterized the variation by a combination of electrospray ionisation mass spectrometry and DNA sequence analysis followed by oxygen-binding experiments. Functional studies outlined an increased oxygen affinity, reduced effect of organic phosphates and a reduced Bohr effect with respect to HbA. In view of the primary role of this interface in the cooperative quaternary transition from the T to R conformational state, a theoretical three-dimensional model of Hb Santa Clara was generated. Structural investigations suggest that replacement of Asn for His beta 97 results in a significant stabilization of the high affinity R-state of the haemoglobin molecule with respect to the low affinity T-state. The role of beta FG4 position has been further examined by computational models of known beta FG4 variants, namely Hb Malmö (beta 97His-->Gln), Hb Wood (beta 97His-->Leu), Hb Nagoya (beta 97His-->Pro) and Hb Moriguchi (beta 97His-->Tyr). These findings demonstrate that, among the various residues at the alpha(1)beta(2) (and alpha(2)beta(1)) intersubunit interface, His beta FG4 contributes significantly to the quaternary constraints that are responsible for the low oxygen affinity of human deoxyhaemoglobin.
De Rosa
Maria Cristina
MC
Institute of Biochemistry and Clinical Biochemistry, Catholic University of Rome, Largo F. Vito I, 00168 Rome, Italy.
Carelli Alinovi
Cristiana
C
Schininà
Maria Eugenia
ME
Clementi
Maria Elisabetta
ME
Amato
Antonio
A
Cappabianca
Maria Pia
MP
Pezzotti
Michela
M
Giardina
Bruno
B
D000328:Adult; D001216:Asparagine / Q000235:genetics* / Q000502:physiology; D001665:Binding Sites / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D006455:Hemoglobins, Abnormal / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D006639:Histidine / Q000235:genetics* / Q000502:physiology; D006801:Humans; D007223:Infant; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
D006455:Hemoglobins, Abnormal; C487907:hemoglobin Santa Clara; D006639:Histidine; D001216:Asparagine; D010100:Oxygen