Krueger J K, Olah G A, Rokop S E, Zhi G, Stull J T, Trewhella J
Chemical Science and Technology Division, Los Alamos National Laboratory, New Mexico 87545, USA.
Biochemistry. 1997 May 20;36(20):6017-23. doi: 10.1021/bi9702703.
Calmodulin (CaM) is the major intracellular receptor for Ca2+ and is responsible for the Ca2+-dependent regulation of a wide variety of cellular processes via interactions with a diverse array of target enzymes. Our current view of the structural basis for CaM enzyme activation is based on biophysical studies of CaM complexed with small peptides that model CaM-binding domains. A major concern with interpreting data from these structures in terms of target enzyme activation mechanisms is that the larger enzyme structure might be expected to impose constraints on CaM binding. Full understanding of the molecular mechanism for CaM-dependent enzyme activation requires additional structural information on the interaction of CaM with functional enzymes. We have utilized small-angle X-ray scattering and neutron scattering with contrast variation to obtain the first structural view of CaM complexed with a functional enzyme, an enzymatically active truncation mutant of skeletal muscle myosin light chain kinase (MLCK). Our data show that CaM undergoes an unhindered conformational collapse upon binding MLCK and activates the enzyme by inducing a significant movement of the kinase's CaM binding and autoinhibitory sequences away from the surface of the catalytic core.
钙调蛋白（CaM）是细胞内主要的Ca2+受体，通过与多种靶酶相互作用，负责多种细胞过程的Ca2+依赖性调节。我们目前对CaM酶激活结构基础的认识基于对与模拟CaM结合域的小肽复合的CaM进行的生物物理研究。根据靶酶激活机制解释这些结构数据时，一个主要问题是，较大的酶结构可能会对CaM结合施加限制。要全面了解CaM依赖性酶激活的分子机制，需要有关CaM与功能酶相互作用的更多结构信息。我们利用小角X射线散射和对比度变化的中子散射技术，首次获得了与功能酶——骨骼肌肌球蛋白轻链激酶（MLCK）的酶活性截短突变体复合的CaM的结构视图。我们的数据表明，CaM与MLCK结合后会发生不受阻碍的构象塌陷，并通过诱导激酶的CaM结合序列和自抑制序列从催化核心表面显著移动来激活该酶。
