Adamian Larisa, Liang Jie
Department of Bioengineering, University of Illinois at Chicago, IL 60607, USA.
Cell Biochem Biophys. 2003;39(1):1-12. doi: 10.1385/CBB:39:1:1.
Ca2+-transporting adenosine triphosphatase (ATPase) of sarcoplasmic reticulum couples ATP hydrolysis with ion transport. Phosphorylation of the cytosolic region of the calcium-bound conformation (E1) of the protein leads to drastic conformational rearrangements of the transmembrane helices and the release of Ca2+. The resulting calcium-free conformation (E2) is less stable than the E1 form. The changes in van der Waals interactions and interhelical hydrogen bonding in the E1 and E2 conformations were compared. Conformational changes in the transmembrane region concomitant with the release of Ca2+ mainly affect the number of interhelical hydrogen bonds, which is reduced to half of that in E1 form, whereas the number of interhelical atomic pairwise contacts reflecting van der Waals interactions experience little change. The interhelical hydrogen bonds in Ca2+-transporting ATPase can be divided into two groups according to their roles: those that play a structural stabilizing role and those that are important for the correct geometry of the Ca2+ binding site. Interhelical hydrogen bonds in the transmembrane regions play important roles for the stability and specificity of helix-helix interactions in proteins where change of conformation is required for transport of ions or small molecules.
肌浆网的钙离子转运三磷酸腺苷酶（ATP酶）将ATP水解与离子转运偶联起来。该蛋白钙离子结合构象（E1）的胞质区域发生磷酸化会导致跨膜螺旋发生剧烈的构象重排以及钙离子的释放。由此产生的无钙构象（E2）不如E1形式稳定。比较了E1和E2构象中范德华相互作用和螺旋间氢键的变化。伴随钙离子释放的跨膜区域构象变化主要影响螺旋间氢键的数量，该数量减少至E1形式的一半，而反映范德华相互作用的螺旋间原子成对接触数量变化不大。钙离子转运ATP酶中的螺旋间氢键可根据其作用分为两组：起结构稳定作用的和对钙离子结合位点正确几何形状重要的。跨膜区域的螺旋间氢键对于蛋白质中螺旋 - 螺旋相互作用的稳定性和特异性起着重要作用，在这些蛋白质中，离子或小分子的转运需要构象变化。
