Effects of beta 6 amino acid hydrophobicity on stability and solubility of hemoglobin tetramers.
The relationship between different amino acids at the beta 6 position of hemoglobin and tetramer stability was addressed by a site-directed mutagenesis approach. Precipitation rates during mechanical agitation of oxyhemoglobins with Gln, Ala, Val, Leu and Trp at the beta 6 position increased 2, 5, 13, 21 and 53 times, respectively, compared with that for Hb A. There was a linear relationship between the log of the precipitation rate constant and amino acid hydrophobicity at the beta 6 position, suggesting that enhanced precipitation of oxy Hb S during mechanical agitation results in part from increased hydrophobicity of beta 6 Val. Deoxyhemoglobin solubility increased in the order of beta 6 Ile, Leu, Val, Trp, Gln, Ala and Glu suggesting that hydrophobic interactions between beta 6 Val and the acceptor site of another hemoglobin molecule during deoxy-Hb S polymerization not only depend on hydrophobicity but also on stereospecificity of the amino acid side chain at the beta 6 position. Furthermore, our results indicate that hydrophobic amino acids at the beta 6 position which promote tetramer instability in the oxy form do not necessarily promote polymerization in the deoxy form.
Adachi
K
K
Children's Hospital of Philadelphia, Department of Pediatrics, PA 19104.
Kim
J Y
JY
Konitzer
P
P
Asakura
T
T
Saviola
B
B
Surrey
S
S
D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D016297:Mutagenesis, Site-Directed; D010108:Oxyhemoglobins / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D011994:Recombinant Proteins; D012995:Solubility; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship
D006454:Hemoglobins; D010108:Oxyhemoglobins; D011994:Recombinant Proteins