l - People

possibility that unexpected results are not necessarily incorrect, but may reflect
undiscovered phenomena.
Calmodulin, calcium free (closed) form
Morph ID: f964492-8654 PDB ID: 1CFD
HAG hinges (residues 80,81)
Calmodulin, like the closely related Troponin C, belongs to a superfamily of homologous
proteins that bind calcium through similar domains. Calmodulin is found in all
eukaryotic cells, mediating various physiological processes. Despite the wide variety of
organisms in which it is found, the sequence is surprisingly well conserved, In all known
sequences, there are only seven amino acid substitutions, all conservative. Calmodulin
contains four Ca 2+ binding EF hands, numbered I-IV, which induce significant
conformational change, leading to its ability to interact with a wide variety of enzymes.
It shares helices A through H with Troponin C (see description of that protein for more
details), but not helix N.
The long central helix, from residues 65 to 92, has a cluster of negatively charged
residues in the central portion, with mostly hydrophobic residues on each end. The
hydrogen bond distances along the helix have variations at four- to five-residue intervals.
The backbone dihedral angles also show deviations from ideal α-helical geometry,
reflecting partial unwinding and apparent strains. The periodic backbone carbonyl
oxygen to N-H hydrogen bonds are longer than usual in this region, Residues 76 to 82
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