Binding change model

An account of the historical development and current state of the binding-change model, written by its principal architect. 

The nucleotide occupancy of the catalytic sites observed in the first crystal structure was exactly what Paul Boyer had predicted earlier in his binding-change model of cooperative catalysis (Boyer, 1993). Consequently, this first high-resolution structure of the Fj-ATPase immediately initiated a number of studies that ultimately led to the elucidation of the F -. TPase s rotational mechanism of cooperative catalysis. At the time, the F - ATPase structure represented the largest asymmetric structure solved to atomic resolution by x-ray crystallography, and this accomplishment, together with the visionary prediction of rotary catalysis, was subsequently awarded the 1997 Nobel prize in chemistry (to John Walker for the structure and Paul Boyer for the catalytic mechanism). However, whether the first (and many subsequent) structure (s) represented physiologically... 

Fig. 12. Proposed binding change model for FiFo-ATPases. [Modified from Boyer (64).]...

Fig. 10-32 Boyer s binding change model of F ATPase. The black triangle represents the y subunit.

Fig. 3. Modified model of the binding change mechanism highlighting cooperativity and including tightly bound ADP and P as intermediates (simplified and redrawn from [14])...

In this chapter, we will describe the composition of the phosphorylating enzyme of chloroplasts as determined by SDS-gel electrophoresis and its structure as revealed by electron microscopy. These studies led to a preliminary model for the chloroplast ATP synthase. The remainder of the chapter will be devoted to two main topics (photo)phosphorylation powered by proton translocation as described by Mitchell s chemiosmotic theory V and recent investigations of the structure and function of the phos-phorylating enzyme in relation to Paul Boyer s binding-change mechanism and a model involving... 

Fig. 27. Illustration of the binding change mechanism for ATP synthesis by the proton-translocating ATP synthase. F, has three chemically identical but conformationally distinct Interacting subunits designated as 0" [open], "L" [loose] and "T [tight] see text forfurfher details on how the three catalytic [ap] sites pass through three conformational states driven by proton flux. Figure modeled after Cross (1981) The mechanism and reguiation of ATP synthesis by F -ATPases. Annu Rev Biochem 50 687.

Rotation of the. Y-Subunit in theEcF,-ATP Svnthase. Duncan,Cross and coworkers carried out additional experiments to see whether the y-subunit would, through its rotation during the catalytic cycle, interact sequentially with each of the p-subunits, as predicted by the rotary model of the binding change mechanism. The design ofthe experiment is illustrated in Fig. 32. 

With the development of the theory of the binding-change mechanism and the investigations that have provided evidence for the rotary motion ofthe y-subunit, the y s subcomplex, or even the c-subunit oligomer of Fq, anew model that is more detailed than that shown earlier in Fig. 6 for the Fo F -ATP synthase has evolved. Before we present the current model for the Fq Fi-ATP synthase, we will briefly review information obtained by NMR studies for the structure of the smaller 8 and e subunits of F, and also some structure information obtained by X-ray crystallography in the case ofthe e-subunit. The structure ofthe Fo-subunits a, b and c will also be described. 

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