Hybrid cluster

Fig. 9. An overall view of the Fepr molecule from D. vulgaris showing the three domains. Domain 1 is predominantly a-helical and contains an unusual configuration of two three-helix bundles approximately perpendicular to one another (see Fig. 11). Domains 2 and 3 have central /3-sheets surrounded by helices. The two Fe-S clusters are at the center of the figure the hybrid cluster is on the left, and located near the interfaces of the three domains.

Cluster 2 appears to be unique among Fe-S-containing proteins whose structures have so far been determined, emd it has been termed the hybrid cluster (6) because of its diverse chemical nature. Figure 14 is a schematic drawing of the cluster as interpreted from the final electron density synthesis and the structure refinement. The cluster contains both oxygen and sulfur bridges, and X represents a site whose precise nature has not been determined, but which may contain a partially occupied and/or disordered substrate molecule (see Section III,B,3,b). The environments of the four iron atoms can be described as follows. 

Prismane valency refers to the old model assuming the presence of a [6Fe-6S] cluster (7). Hybrid cluster refers to the 4Fe cluster found to be present in the crystal structure. 

Fig. 1. Iron-sulfur clusters basic building blocks. In most cases the iron is tetrahe-drally coordinated by sulfur from cysteinyl residues (and labile sulfur). Variability on coordination is allowed (see text). A, Rubredoxin type FeS4 (simplest cluster, no labile sulfur) B, plant-type ferredoxin [2Fe-2S] C, bacterial ferredoxin [3Fe-4S] D, bacterial ferredoxin and HiPIP [4Fe-4S] E, novel cluster [4Fe-2S, 20] ( hybrid cluster ).

FIGURE 12.3 S = 9/2 EPR of Desulfovibrio desulfuricans hybrid cluster protein. Note the weak low-field peak with g > 14 and the relatively strong intensities in the g 5.4 and g 6.4 regions, which are all characteristics of the S = 9/2 system. 

In the same vein one must mention the recently reported hybrid clusters 6 ... 

An interesting new tetranuclear iron hybrid cluster protein (HCP) has been observed and characterized from two sulfate reducing bacteria. Combined X-ray diffraction and EPR data showed that it contains both oxygen and sulfur bridges between the iron ions. The nature of the cluster was found to be independent of the presence or absence of oxygen in the sample preparation.247... 

Thus, the hybrid cluster is a putative iron-sulfur redox catalyst. It is, however, a very uncommon cluster (perhaps only comparable to the nitrogenase active site) in two aspects (1) it is a hybrid cluster i.e., it contains intrinsic building blocks that are distinctly strange to iron-sulfur clusters and (2) it can exist in more than two (in fact, four [63]) oxidation states. 

Figure 5 A sketch of the structure of the hybrid cluster in the prismane protein. The approximate core structure is [4Fe-2S-20]. Cys406 carries a persulfido sulfur. X is an unidentified bridge of low occupancy in the crystal structure.

PFO puruvate ferredoxin oxidoreductase, HCP hybrid cluster protein, PNO... 

PFO puruvateiferredoxin oxidoreductase, HCP hybrid cluster protein, PNO pyruvate NADH oxidoreductase, Nbp35 P-loop NTPase, Nar/Narf hydrogenase-like protein, Rli ATP-binding cassette protein... 

Hackstein JHP, Akhmanova A, Boxma B, Harhangi HR, Voncken FGJ (1999) Hydrogenosomes eukaryotic adaptations to anaerobic environments. Trends Microbiol 7 441-447 Han KL, Yong TS, Ryu JS, Hwang UW, Park SJ (2004) Identification of the hybrid cluster protein, HCP, from amitochondriate eukaryotes and its phylogenetic implications. J Microbiol Biotechnol 14 134-139... 

Identification of Groupings of Graph Theoretical Descriptors Using a Hybrid Cluster Analysis Approach. 

Here, Xni l) denotes the harmonic oscillator wave-functions, (pa(r) and (pb(r) correspond to the states of electrons localized on a and b ions, the index v numbers the hybrid cluster states in the molecular field. It should be noted that, within the scope of the adopted approach, the quantum properties of the vibronic states in a self-consistent field are taken into account. Therefore, it is reasonable to call the proposed approximation quasidynamical. The vibronic states obtained within the scope of the quasidynamical approach are hybrid, i.e. retaining the quantum properties of both electronic and vibrational states. In the case of strong vibronic coupling, i.e. in the case of adiabatic potentials possessing deep minima both the... 

Taraviras, S.L., Ivanciuc, O. and Cabrol-Bass, D. (2000) Identification of groupings of graph theoretical molecular descriptors using a hybrid cluster analysis approach. /. Chem. Inf. Comput. Sci., 40, 1128-1146. 

---