Ca2+-free calmodulin (apocalmodulin) binds target proteins and alters their function. Apocalmodulin has roles in the cell that apparently do not require the ability to bind Ca2+ at all, and these roles appear to be essential for cell's metabolism. Small-angle X-ray scattering (SAXS) results indicate that the overall conformation of apocalmodulin remains unchanged, but the conformation for the C-domain changes from the closed to semi-open conformation upon binding the target proteins. The conformational change would be induced by electrostatic interactions and subsequent van der Waals interactions and it can cause changes in the Ca2+ affinity of the apocalmodulin-target protein complex. An analysis of residue pairs between calmodulin and target peptides suggests that apocalmodulin recognizes Ca2+-dependent calmodulin binding proteins, utilizing a new motif different from IQ motif.
Flavoproteins are involved in many different biological events from biological oxidations to apoptosis. This versatility might come from cross talk between the flavin molecule and amino acid residues in the active site. Physicochemical approaches on the relationship between structure and function of the flavin and the protein in L-lactate oxidase are reported here to solve the common reaction mechanism of enzymes of the α-hydroxy-acid oxidase family.