Goch Grazyna, Maciejczyk Maciej, Oleszczuk Marta, Stachowiak Damian, Malicka Joanna, Bierzyński Andrzej
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, ul. Pawińskiego 5A, 02-106 Warsaw, Poland.
Biochemistry. 2003 Jun 10;42(22):6840-7. doi: 10.1021/bi027339d.
It is not certain whether the helix propagation parameters s(n)() (i.e., the equilibrium constants between (n - 1)- and n-residue long alpha-helices) determined from numerous studies of rather long model peptides are applicable for description of the initial steps of the helix formation during the protein folding process. From fluorescence, NMR, and calorimetric studies of a series of model peptides, containing the La(3+)-binding sequence nucleating the helix (Siedlecka, M., Goch, G., Ejchart, A., Sticht, H., and Bierzynski, A. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 903-908), we have determined, at 25 degrees C, the average values of the enthalpy DeltaH(n)() and of the helix growth parameters s(n)() describing the first four steps of helix propagation in polyalanine. The absolute values of the C-cap parameters, describing the contribution of the C-terminal residues to the helix free energy, have also been estimated for alanine (1.2 +/- 0.5) and NH(2) group (1.6 +/- 0.7). The initial four steps of the helix growth in polyalanine can be described by a common propagation parameter s = 1.54 +/- 0.04. The enthalpy DeltaH(n)() is also constant and equals -980 +/- 100 cal mol(-)(1).
从众多对相当长的模型肽的研究中确定的螺旋传播参数s(n)（即(n - 1)残基长和n残基长的α-螺旋之间的平衡常数）是否适用于描述蛋白质折叠过程中螺旋形成的初始步骤尚不确定。通过对一系列含有能引发螺旋的镧(3+)结合序列的模型肽进行荧光、核磁共振和量热研究（Siedlecka, M., Goch, G., Ejchart, A., Sticht, H., and Bierzynski, A. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 903 - 908），我们在25℃下确定了描述聚丙氨酸中螺旋传播前四步的焓变ΔH(n)和螺旋生长参数s(n)的平均值。还估算了丙氨酸（1.2±0.5）和氨基（1.6±0.7）的C-帽参数的绝对值，该参数描述了C末端残基对螺旋自由能的贡献。聚丙氨酸中螺旋生长的前四步可用共同的传播参数s = 1.54±0.04来描述。焓变ΔH(n)也是恒定的，等于-980±100 cal mol(-)(1)。
