Conformational transitions of calmodulin as studied by vacuum-UV CD

✍ Scribed by John P. Hennessey Jr.; Parthasarathy Manavalan; W. Curtis Johnson Jr.; Dean A. Malencik; Sonia R. Anderson; Michael I. Schimerlik; Yechiel Shalitin

• Publisher: Wiley (John Wiley & Sons)
• Year: 1987
• Tongue: English
• Weight: 661 KB
• Volume: 26
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360260409

✦ Synopsis

Synopsis

CD measurements were made for calmodulin and its calcium (Ca2') complexes at different ionic strengths and Ca2+ concentrations. Calmodulin at an ionic strength of O.OOM and in the absence of Ca" exists as an a-helical protein with a negligible amount of 8-sheet. An increase in ionic strength, whether or not Ca2' is present, increases a-helix at the expense of "other" (coil) structure. The changes in 8-sheet and 8-turns are insignificant. Binding of Ca" at low ionic strength occurs in stages with at least one folding intermediate before attaining the final stable state. Binding of Ca2' at an ionic strength of 0.165M causes only a slight increase in a-helix, so that the secondary structure of the protein depends on ionic strength and is insensitive to the nature of the cation (i.e., Ca"). Thus, the activation of calmodulin by Ca" must be due to a structural reorientation rather than to a major secondary structural alteration. The CD estimation of secondary structure with 4 mol Ca2'/calmodulin (61% a-helix, 2% antiparallel 8-sheet, 2% parallel 8-sheet, 21% 8-turns, and 14% other) is in excellent agreement with the x-ray results.