The homodimeric hemoglobin from Scapharca can be locked into new cooperative structures upon reaction of Cys92, located at the subunit interface, with organomercurials

FEBS Letters

Coletta, Massimiliano²  Chiancone, Emilia¹  Verzili, Daniela¹  Boffi, Alberto¹  Colotti, Gianni¹ 

[1] CNR Center of Molecular Biology, Department of Biochemical Sciences ‘A. Rossi Fanelli’, University ‘La Sapienza’, 00185 Rome, Italy;Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F. Camerini, 2, 62032 Camerino (MC), Italy

关键词: Molluscan hemoglobin;    Cooperativity: Chemical modification;    Conformational change;   

DOI  :  10.1016/0014-5793(92)81531-P

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

In the cooperative, homodimeric hemoglobin from Scapharca inaequivalvis, HbI, the subunit interface is formed by the heme-carrying E and F helices and contains the only cysteine residue of the globin chain (Cys⁹², F2) in an area which changes from hydrophilic to hydrophobic upon oxygenation. Binding of organomercurials to Hbl is cooperative and entails major quaternary rearrangements. The reaction of CYs⁹² with p-chloromercuri-benzoate (PMB) and p-nitro-o-chloromercuriphenol (PN), a sensitive reporter of the cysteine microenvironment at neutral pH values, has been followed in stopped flow experiments. Kinetic evidence for the cooperativity of mercurial binding has been obtained and the rate of the corresponding conformational transition has been estimated. As expected PN, but not PMB, is able to monitor the oxygen-linked change of the cysteine microenvironment. The modification of Cys⁹² with PN has unique functional effects. In PN-reacted Hbl cooperativity is maintained. albeit to a different extent, depending on the ligation state of the protein during mercaptide formation. It may be envisaged that PN locks the protein into new, cooperative, quaternary structures stabilized by hydrogen bonding interactions between the ionized nitrophenol moiety and the contralateral subunit.

【 授权许可】

Unknown