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The homodimeric hemoglobin from Scapharca can be locked into new cooperative structures upon reaction of Cys 92 , located at the subunit interface, with organomercurials
Author(s) -
Colotti Gianni,
Boffi Alberto,
Verzili Daniela,
Coletta Massimiliano,
Chiancone Emilia
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)81531-p
Subject(s) - cooperativity , chemistry , cysteine , moiety , protein subunit , protein quaternary structure , heme , hemoglobin , hydrogen bond , stereochemistry , biophysics , crystallography , biochemistry , molecule , organic chemistry , enzyme , biology , gene
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 (Cys 92 , 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 CYs 92 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 Cys 92 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.