The alpha-helical content of calmodulin is increased by solution conditions favouring protein crystallisation.
The conformation of porcine-brain calmodulin in solution has been examined by far-UV circular dichroism in the presence of 2-methyl 2,4-pentanediol, and polyethylene glycol which are used to promote the crystallisation of calmodulin. These organic compounds increase the alpha-helical content of Ca4-calmodulin to a significant degree and to a level similar to the alpha-helical content deduced from the crystal structure. These results support the view that in aqueous solution at pH 5-7, the conformation of Ca4-calmodulin is significantly different from the crystal structure and probably lacks at least a portion of the central helix. In the process of crystallisation, Ca4-calmodulin apparently adopts additional alpha-helical structure, probably due to the composition of the solution from which crystals are grown.
Bayley
P M
PM
Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London, UK.
Martin
S R
SR
D000818:Animals; D001923:Brain Chemistry; D002147:Calmodulin / Q000737:chemistry* / Q000302:isolation & purification; D002942:Circular Dichroism; D003460:Crystallization; D006018:Glycols; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D012996:Solutions; D013552:Swine
D002147:Calmodulin; D006018:Glycols; D011506:Proteins; D012996:Solutions; C011480:hexylene glycol