Protein crystallization structure levels

The first protein crystal structure, myoglobin, was solved in 1960. The second, lysozyme, followed in 1965. In 1967 three structures were solved ribonuclease, chymotrypsin and carboxypeptidase. Thereafter, the number solved has increased almost exponentially year by year so that by 1979 there were some 161 structures known, at least at the level of tracing the fold of the polypeptide chain [6]. To date, there are well over 200 structures solved, but this number includes several structures of the same protein in a different crystal form or from a different species. Some protein structures are illustrated in Figure 1. 

These redox level issues have not been solved, despite the discovery of the more complicated coordination complexes of the binuclear active sites which might offer greater versatility. Binuclear sites provide the possibility of sharing the two-electron changes by two metals but whether this occurs is not established. The clear result of the protein crystal structures is that the target-model complexes for the active sites are well defined. The next section describes the active sites of [NiFe] and [Fe]H2ases. 

Despite the above noted correlation of phenomena, current descriptions of molecular structure and resulting function of hemoglobin and myoglobin (as well as of muscle contraction to be addressed at the molecular level in Chapter 8) proceed without consideration of the consilient mechanism. th the consilient mechanism in mind, however, a distinctive way of looking at protein structure and function materializes. The availability of so many protein crystal structures from The Protein Data Bank and, as employed in our case, the capacity to... 

Figure 18.4 Structures of heme/Cu oxidases at different levels of detail, (a) Position of the redox-active cofactors relative to the membrane of CcO (left, only two obligatory subunits are shown) and quinol oxidase (right), (b) Electron transfer paths in mammalian CcO. Note that the imidazoles that ligate six-coordinate heme a and the five-coordinate heme are linked by a single amino acid, which can serve as a wire for electron transfer from ferroheme a to ferriheme as. (c) The O2 reduction site of mammalian CcO the numbering of the residues corresponds to that in the crystal structure of bovine heart CcO. The subscript 3 in heme as and heme 03 signifies the heme that binds O2. The structures were generated using coordinates deposited in the Protein Data Bank, lari [Ostermeier et al., 1997] Ifft [Abramson et al., 2000] (a) and locc [Tsukihara et al., 1996] (b, c).

Various isoforms of both HO and NOS can be expressed in recombinant systems. As a result, the immediate future will undoubtedly witness a wealth of mutagenesis experiments guided by the crystal structures. It also may be possible to trap in crystalline form the various intermediates of the HO reaction cycle, which will greatly facilitate a deeper understanding of the catalytic mechanism. Conformational dynamics appear to be quite important in HO, and hence, a variety of spectral probes such as NMR and fluorescence should prove especially useful in studying the role of protein dynamics in function. Overall there should be considerable optimism for understanding HO at the level of detail achieved for peroxidases and other well-studied enz5une systems. 

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