The so-called “falling cat” problem, which is concerned with the coupling between internal motions and rotations of a flexible body, is introduced. I give a geometric interpretation of the Eckart condition, which is frequently used for the approximate separation of rotations and internal motions of polyatomic molecules. It is shown that the separation procedure based on the Eckart condition disregards the intrinsically “curved” nature of molecular internal space (shape space). The “curved” nature of shape space is shown to have considerable effects on structural transition dynamics of polyatomic molecules.
Cell motility, including smooth muscle contraction and cell migration, is regulated by reversible phosphorylation of myosin. Recent studies have shown that myosin phosphatase (MP), along with kinases, contributes dynamically to the regulation of myosin-II phosphorylation. An MP specific inhibitor named CPI-17, which is expressed in smooth muscle and neuronal cells, mediates receptor signaling leading to myosin-II phosphorylation. In this review, we discuss structure/function relationships of CPI-17 stemming from our recent NMR studies and computer modeling results. The combination of biophysical approaches with biochemical techniques has revealed the inhibitory mechanism of CPI-17.
Structural changes in cytochrome P450 camphor monooxygenase (P450cam) upon the binding of the electron donor, putidaredoxin (Pdx), have been believed to be crucial for the P450cam catalysis. However, the regulation mechanism for the P450cam-catalyzed reaction by Pdx binding, so-called “effector function” of Pdx, was unclear due to the lack of the structural information on the Pdx-induced structural changes in P450cam. Here we summarize the recent progress in characterizing the Pdx-induced structural changes in P450cam by using NMR spectroscopy and site-directed mutagenesis. The current information would help us to understand the effector function of Pdx in the P450cam catalysis.
Heme-regulated phosphodiesterase from Escherichia coli (Ec DOS) is a novel PAS heme-sensor enzyme. Ec DOS is active in the Fe2+ heme-bound form, whereas it is inactive in the Fe3+ heme-bound form. To elucidate the mechanism of the redox-dependent heme-regulated catalysis, we examined spectroscopic and functional characters of site-directed and deletion mutant proteins. We also determined crystal structures of the wild type enzyme under various conditions. In this review, we summarized findings about heme-sensor proteins, PAS domain and phosphodiesterase in general and structure and function relationships of Ec DOS specifically.