Hb Villaverde [beta 89 (F5) Ser-->Thr]: the structural modification of an intrasubunit contact is responsible for a...

Hb Villaverde [beta 89 (F5) Ser-->Thr], identified in a Spanish patient, is a new human hemoglobin variant, electrophoreticaly silent, responsible for a severe erythrocytosis. This abnormal hemoglobin displays a very high oxygen affinity and a markedly reduced cooperativity that is partly restored in the presence of IHP. Determination of the structural abnormality was achieved on a mixture of the normal and abnormal beta-chains. After isolation of the abnormal tryptic peptide by RP-HPLC, its sequence was determined by mass spectrometry. The structural abnormality disturbs the intrasubunit interaction between helices F and H and, thus, may weaken the C-terminal bonds of the deoxy conformation and the heme contacts of several hydrophobic residues. Hb Villaverde demonstrates that this intrasubunit contact between helices F and H is essential for the cohesion of the hemoglobin molecule.