Cytochrome domain interactions

Sevrioukova, I., and Peterson, J. A. 1996. Domain-domain interaction in cytochrome P450BM-3. Biochimie, 78,744-751. 

FIGURE 7. Stereo diagram of one subunit of flavocytochrome b. Only residues ln486 are shown, the remainder being involved in intermolecular interactions. The flavin-binding domain is at the top and the cytochrome domain is at the bottom. The flavin and heme groups are shown as skeletal models. 

The characterisation of the complexation between flavocytochrome b2 and cytochrome c has been the subject of many studies (see for example Short et al., 1998 Daff et al., 1996b and CapeillEre-Blandin, 1995). Work on the anomala flavocytochrome b2, for which there is no crystal structure, led to the conclusions that the cytochrome c binding site involved both the flavodehydrogenase and cytochrome domains (CapeillEre-Blandin and Albani, 1987) and that the complex was stabilised by electrostatic interactions (CapeillEre-Blandin, 1982). It is clear that similar conclusions hold true for the S. cerevisiae enzyme (Daff et al., 1996b) for which the crystal... 

NMR at 400 MHz has been used to probe the mobility of the cytochrome domain within the holoenzyme (84). The linewidths of heme resonances downfield of 4-12 ppm and upheld of -4 ppm have been compared for the holoenzyme and the cytochrome 62 core and indicate that the cytochrome domains of the holoenzyme are markedly mobile (84). NMR has also been used to investigate the nature of the interaction between flavocytochrome 62 and cytochrome c (85,86) with the ultimate aim of defining the binding site on flavocytochrome 62 used by its physiological partner. The extensive NMR studies on the interaction between cytochrome 65 and cytochrome c (87,88) provide a useful background to the work with cytochrome 62 ... 

Unlike DAAO, the crystal structure of F 2 does not clarify the mechanism of flavin reduction. The monomer of F 2 has a small N-terminal cytochrome domain and a larger C-terminal a/(3 barrel containing FMN, connected by a short linker. The carboxylate of the product makes a salt bridge and a hydrogen bond to an Arg and a Tyr (Figure 3), residues also present in DAAO. Unlike in DAAO, the product in the crystal structure interacts with both Tyr254 and His373, either of which could be the active site base needed in a carbanion mechanism. " The substrate, lactate, has been modeled into the structure in two different conformations. ... 

Sevrioukova, I.F., J.T. Hazzard, G. Tollin, and XL. Poulos (1999). The FMN to heme electron transfer in cytochrome P450BM-3. Effect of chemical modification of cysteines engineered at the FMN-heme domain interaction site. J. Biol. Chem. 274, 36097-36106. 

S Role of the FMN Domain and Connecting Domain in the Cytochrome P450 Interaction... 

Apaf-1 possesses a region homologous to the procaspase-prodomain, known as the caspase-recruiting domain (CARD) at the N terminus, a region homologous to CED-4 in the middle part and WD-40 repeat structure that appears to be involved in protein-protein interactions. The released cytochrome c interacts with two cytosolic proteins, Apaf-1 and procaspase-9, and dATP/ATP in the cytoplasm to form a complex known as... 

BH3 domain) of the BH3-only proteins binds to other Bcl-2 family members thereby influencing their conformation. This interaction facilitates the release of cytochrome C and other mitochondrial proteins from the intermembrane space of mitochondria. Despite much effort the exact biochemical mechanism which governs this release is not yet fully understood. The release of cytochrome C facilitates the formation of the apoptosome, the second platform for apoptosis initiation besides the DISC. At the apoptosome which is also a multi-protein complex the initiator caspase-9 is activated. At this point the two pathways converge. 

In be complexes bci complexes of mitochondria and bacteria and b f complexes of chloroplasts), the catalytic domain of the Rieske protein corresponding to the isolated water-soluble fragments that have been crystallized is anchored to the rest of the complex (in particular, cytochrome b) by a long (37 residues in bovine heart bci complex) transmembrane helix acting as a membrane anchor (41, 42). The great length of the transmembrane helix is due to the fact that the helix stretches across the bci complex dimer and that the catalytic domain of the Rieske protein is swapped between the monomers, that is, the transmembrane helix interacts with one monomer and the catalytic domain with the other monomer. The connection between the membrane anchor and the catalytic domain is formed by a 12-residue flexible linker that allows for movement of the catalytic domain during the turnover of the enzyme (Fig. 8a see Section VII). Three different positional states of the catalytic domain of the Rieske protein have been observed in different crystal forms (Fig. 8b) (41, 42) ... 

Fig. 12. Crystal structure of the complex formed between the heme and FMN domains of cytochrome P450BM-3 133). The FMN domain docks on the proximal surface of the heme domain. The thicker trace in the heme domain highlights residues 387 to the heme ligand, Cys400. This section of polypeptide contacts the FMN and might provide an electron transfer conduit to the heme ligand. The two interacting surfaces are electrostatically complementary, with similar complementarity expected for HO and NOS.

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