Functional cycle

How does the GroEL-GroES complex function as a chaperone to assist protein folding Although several aspects of the mechanism are not clear, the main features of the functional cycle are known. The first step is the... 

II. Classic Division of the Hydrocarbon Functionalization Cycle into Three Parts... 

Among the very few catalytic systems that allow not only C-H bond activation but also functionalization are those based on platinum(II) catalysts. Soon after the discovery that platinum salts in aqueous solution catalyze H/D exchange in hydrocarbons (9,10 a hydrocarbon functionalization cycle was developed on the basis of this system (11). This cycle is depicted in Scheme 2. 

Fig. 5.16. Functional cycle of the heterotrimeric G-proteins. a) The G-proteins exist in the ground state as a heterotrimeric complex (G GDP) (Py)- b) The activated receptor binds to the inactive heterotrimeric complex of the G-protein and leads to dissociation of the bound GDP and the Pyeomplex. c) Binding of GTP to the empty G -subunit transforms the latter into the active G GTP state. G GTP interacts with an effector molecule in the sequence El and activates the latter for further signal transmission. The released Py-complex may also take part in signal conduction by binding to a corresponding effector molecule E2 and activating the latter for further signal conduction, d) Hydrolysis of the bound GTP terminates the signal transduction via the a-subunit.

Originally, it was assumed that the Py-complex only played a passive role in the functional cycle of the G-proteins. It soon became apparent, however, that the Py-complex, in addition to binding to the a-subimit, also carries out other functions and interacts specifically with corresponding effector molecules (review article Neer, 1995). Tlie Py-complex must be assigned its own regulatory function, it takes part itself in the propagation and termination of signal transmission. 

Clearly, CTI leads to a periodic backbone contraction/expansion of the polypeptide chain involved, as could be inferred from the isomer-specific distances of the Ca atoms directly attached to the isomerizing peptide bond. For prolyl bonds in native proteins this distance is about 0.8 A shorter in the cis isomer when compared to the respective trans isomer [12]. This atomic translation produces a mechanical moment that was hypothesized to be involved in the functional cycle of motor proteins [13]. 

Figure 10.26 A schematic diagram of the functional cycle of the Na+-K+ pump. 

Chaperones are involved at all stages of cellular metabolism, during protein biosynthesis and maturation, in protection from environmental stress, in rearrangements of cellular macromolecules during functional cycles of assembly and disassembly, and finally in targeting proteins for degradation. 

Van Wynsberghe, A., Li, G., Cui, Q. Normal-mode analysis suggests protein flexibility modulation throughout RNA polymerase s functional cycle, Biochem. 2004, 43,13083. 

The specific system that we use to explore these questions is the conventional myosin, also termed myosin 11, which plays key physiological functions in muscle contraction and cell division. It is an ideal system for in-depth theoretical and computational analysis because its structural and kinetic properties have been characterized by a large body of diverse experimental techniques." For example, at the time our research was initiated, myosin 11 was one of the few motor systems for which high-resolution x-ray structures are available for multiple functional states " since then, multiple high-resolution x-ray structures have also been obtained for myosin V and VI, two other widely studied members of the myosin superfamily that are more processive in nature compared to myosin 11. The functional cycle of myosin 11 is best described by the celebrated Lymn-Taylor schane (Figure 2.1a)," in which... 

Five-coordinate alkyl Pt(rv) complexes have been proposed as short-lived intermediates in platinum-catalyzed alkane functionalization cycles. Hence, interest in preparing suitable complexes to enable their chemistry to be studied has arisen.Novel five-coordinate platinum(iv) alkyl complexes with a variety of /3-diiminate ligands have been prepared and have been shown to be useful precursors to unsaturated Pt(ll) species for alkane. Stoichiometric alkane dehydrogenation was observed using either a five-coordinate Pt(iv) species or an olefin hydride complex. Mechanistic proposals were based on NMR spectroscopic measurements and, in one case, on X-ray crystallographic characterization of a product. Kinetic details were not reported in this communication, but the systems hold potential promise, and conversion to a catalytic system may be feasible upon further investigation. 

In particular, as a step in the functional cycle of the myosin II motor, ATP binding occurs at a water-filled cleft." In the scallop muscle, as shown below, the water-filled cleft can be seen to communicate in two directions. In one direction it communicates with the hydrophobic... 

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