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Structure of deoxyhemoglobin: Ionizable groups and polyethylene glycol
Author(s) -
Saroff Harry A.
Publication year - 2002
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.10258
Subject(s) - dimer , polyethylene glycol , hemoglobin , chemistry , oxygen , salt (chemistry) , molecule , crystallography , torr , polyethylene , polymer chemistry , organic chemistry , thermodynamics , physics
X‐ray studies on deoxy‐hemoglobin have been reported on crystals grown under conditions of high (about 2.5 M ) and low salt (about 0.1 M ). The high‐salt crystals were grown in water, whereas the low‐salt crystals were prepared in polyethylene glycol solutions (m.w. 6000–8000 Da, 10–30% w/v). Oxygen‐binding characteristics of hemoglobin in these two environments differ radically. In salt solutions, hemoglobin binds oxygen with a p50 value of about 5 torr of oxygen and in a cooperative manner characterized with an n value of Hill varying from two to three. In polyethylene glycol solutions, hemoglobin crystals are oxygenated with a p50 value of about 270 torr of oxygen, without exhibiting a cooperative effect. I report on a detailed study of the X‐ray data defining the dimer interface (α1β2) of these two forms of hemoglobin. The study reveals that the main difference between the two structures lies in the number and arrangement of the water molecules and in distances between ionizable side chains in the dimer interface. I propose that these differences lead to significant shifts in the pK values of the ionizable groups in the dimer interface. Proteins 2003;50:329–340. © 2002 Wiley‐Liss, Inc.