Blood, 1 July 2002, Vol. 100, No. 1, pp. 283-288
RED CELLS
Nuclear magnetic resonance studies of mutations at the
tetramerization region of human alpha spectrin
Sunghyouk Park,
Michael E. Johnson, and
Leslie W.-M. Fung
From the Center for Pharmaceutical Biotechnology,
University of Illinois at Chicago; and the Department of Chemistry,
Loyola University of Chicago, IL.
Many spectrin mutations that destabilize tetramer formation and
lead to hereditary hemolytic anemias are located at the N-terminal region of 
-spectrin, with the Arg28 position considered to
be a mutation hot spot. We have introduced mutations at positions 28 and 45 into a model peptide, Sp1-156, consisting of the first 156 residues in the N-terminal region of -spectrin (N). The association of these -spectrin peptides that have single amino acid
replacements with a 
-spectrin model peptide, consisting of the
C-terminal region of -spectrin (C), was determined, and structural changes due to amino acid replacements were monitored by
nuclear magnetic resonance (NMR). We found evidence for similar and
very localized structural changes in Sp1-156Arg45Thr and Sp1-156Arg45Ser, although these 2 mutant peptides associated with
-spectrin peptide with significantly differing affinities. The
Sp1-156Arg28Ser peptide showed an affinity for the -spectrin peptide comparable to that of Sp1-156Arg45Ser, but it exhibited substantial and widespread spectral changes. Our results suggest that
both Arg45 replacements induce only minor structural perturbations in
the first helix of Sp1-156, but the Arg28Ser replacement affects both the first helix and the following structural domain. Our results
also indicate that the mechanism for reduced spectrin tetramerization
is through mutation-induced changes in molecular recognition at the
-tetramerization site, rather than through conformational
disruption, as has been suggested in prior literature.
