| Abstract: | In normal deoxyhemoglobin A, the beta chain COOH-terminal peptide adopts a well ordered structure which is needed for the full expression of allosteric action. Our crystallographic studies of deoxyhemoglobin Creteil (beta 89 Ser replaced by Asn), a variant hemoglobin characterized by high oxygen affinity and a very low level of allosteric function, show that replacement of Ser 89 beta by asparagine causes severe disordering of the beta chain COOH-terminal tetrapeptide. This results, as shown by our spectroscopic studies, in the destabilization of the quaternary structure of deoxyhemoglobin Creteil. We find, furthermore, that the changes in tertiary structure observed in deoxyhemoglobin Creteil are common to other variant hemoglobins having similar functional abnormalities but very different changes in primary structure. In particular, direct comparison of the difference electron density map of deoxyhemoglobin Creteil with that of deoxyhemoglobin Nancy (beta 145 Tyr replaced by Asp) suggests that these two abnormal hemoglobins may have the same mechanism of dysfunction despite the very different nature of their respective sequence changes. |
