After over a century of extensive research, hemoglobin has become the
prototype of allosteric and cooperative proteins. Its molecular structure, known in great
detail, has allowed the design of hundreds of site directed mutations, aimed at interfering
with its function, and thus at testing our hypotheses on the molecular mechanisms of
allostery. The wealth of information thus obtained is difficult to read except for specialists,
not only because it makes use of many different technical approaches, but also because of
its intrinsically patchy nature. Moreover, several researchers have tried to assign specific
roles to segments of the polypeptide chains, rather than to single residues, and have tested
their hypotheses by multiple point mutations or by complete replacement with the
homologous segment from a different hemoglobin to produce chimeric macromolecules.
This approach is in great need of a revision since putative functionally relevant segments
partially overlap. This review briefly describes the structure and function of hemoglobin,
and analyzes the effect of point mutations, multiple mutations and segment replacement,
with special attention to possible biotechnological applications, ranging from
pharmacology (Hb solutions as resuscitating fluids and sources of the protein found in
hemoglobinopathies for biochemical studies) to bioreactors. Occasional reference is made
to site directed mutants of myoglobin, whenever this helps clarifying perplexing results
obtained on hemoglobin.
Human hemoglobin, naturally occurring mutants, site directed
mutants, cooperativity, allosteric core.
Dipartimento di Scienze Biochemiche “A. Rossi Fanelli”, Università degli Studi di Roma “La Sapienza”, Piazzale Aldo Moro 5, 00185 Rome; Italy.