Natively unfolded C-terminal domain of caldesmon remains substantially unstructured after the effective binding to calmodulin.
The structure of C-terminal domain (CaD136, C-terminal residues 636-771) of chicken gizzard caldesmon has been analyzed by a variety of physico-chemical methods. We are showing here that CaD136 does not have globular structure, has low secondary structure content, is essentially noncompact, as it follows from high R(g) and R(S) values, and is characterized by the absence of distinct heat absorption peaks, i.e. it belongs to the family of natively unfolded (or intrinsically unstructured) proteins. Surprisingly, effective binding of single calmodulin molecule (K(d) = 1.4 +/- 0.2 microM) leads only to a very moderate folding of this protein and CaD136 remains substantially unfolded within its tight complex with calmodulin. The biological significance of these observations is discussed.
Permyakov
Sergei E
SE
Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
Millett
Ian S
IS
Doniach
Sebastian
S
Permyakov
Eugene A
EA
Uversky
Vladimir N
VN
D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D002645:Chickens; D002942:Circular Dichroism; D057927:Hydrophobic and Hydrophilic Interactions; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence / Q000379:methods
D000596:Amino Acids; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins