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binding region exists in mammalian cholesterol-metaboliz- ing P-450scc (Lambeth et a/., 1984). The camphor molecule makes van der Waals contacts with various residues (e.g. Phe-87, Leu-244, Val-247, Val-295). This positions the substrate and maintains regioselectivity and stereospecificity of monooxygenation (Poulos et a/., 1987). The only hydrogen bond between camphor and P-450cam is provided by Tyr-96. Muta- genesis of this residue (Y96F) results in lower activity, loss of absolute regiospecificity of hydroxylation, and altered haem iron spin-state equilibrium. Tyr-96 has important roles in maximising the low- to high-spin con- version necessary for electron transfer to the haem and in the co-operativity of association of camphor and potas- sium ions with P-450cam (Sligar ef a/., 1991).

Figure 1 binding region exists in mammalian cholesterol-metaboliz- ing P-450scc (Lambeth et a/., 1984). The camphor molecule makes van der Waals contacts with various residues (e.g. Phe-87, Leu-244, Val-247, Val-295). This positions the substrate and maintains regioselectivity and stereospecificity of monooxygenation (Poulos et a/., 1987). The only hydrogen bond between camphor and P-450cam is provided by Tyr-96. Muta- genesis of this residue (Y96F) results in lower activity, loss of absolute regiospecificity of hydroxylation, and altered haem iron spin-state equilibrium. Tyr-96 has important roles in maximising the low- to high-spin con- version necessary for electron transfer to the haem and in the co-operativity of association of camphor and potas- sium ions with P-450cam (Sligar ef a/., 1991).

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Table 1. Characterized bacterial cytochrome P-450 systems. Characterized bacterial P-450 systems for which primary sequences have been determined are tabulated. Genes encoding non- or poorly characterized P-450 and P-450-like proteins have also been isolated and sequenced from B. subtilis, some Streptomyces, Mycobacterium and Anabaena species, and Rhodococcus fascians. Primary sequences can be located on the worldwide web at site: http: /Avww.icbeg.trieste.it / p450/P450Nom_Bacteria.html
Table 1. Characterized bacterial cytochrome P-450 systems. Characterized bacterial P-450 systems for which primary sequences have been determined are tabulated. Genes encoding non- or poorly characterized P-450 and P-450-like proteins have also been isolated and sequenced from B. subtilis, some Streptomyces, Mycobacterium and Anabaena species, and Rhodococcus fascians. Primary sequences can be located on the worldwide web at site: http: /Avww.icbeg.trieste.it / p450/P450Nom_Bacteria.html
Fig. 2. The structure of cytochrome P-450 eryF. P-450 eryF is the most recently solved P-450 structure (Cupp-Vickery and Poulos, 1995). it catalyses the initial step in erythromycin biosynthesis (6S-hydroxylation of 6-deoxyerythronolide B) in S. erythrea. The Structure (like all other bacterial P-450 structures solved to date) resembles a triagonal prism. Helices are shown as light-blue cylinders, strands as purple ribbons and random coil regions as yellow strings. The haem (red) and substrate (dark blue) are seen at the centre of the molecule.
Fig. 2. The structure of cytochrome P-450 eryF. P-450 eryF is the most recently solved P-450 structure (Cupp-Vickery and Poulos, 1995). it catalyses the initial step in erythromycin biosynthesis (6S-hydroxylation of 6-deoxyerythronolide B) in S. erythrea. The Structure (like all other bacterial P-450 structures solved to date) resembles a triagonal prism. Helices are shown as light-blue cylinders, strands as purple ribbons and random coil regions as yellow strings. The haem (red) and substrate (dark blue) are seen at the centre of the molecule.
Fig. 3. Structural comparison of cytochromes P-450ery F and P-450cam. The overall topology of the bacteria! P-450 structures solved (P-450cam, P-450 BM-3 haem domain, P-450terp and P-450 eryF) is well conserved. The diagram shows a stereo view of an overlay of the structures of P-450 eryF (shaded) and P-450cam (white). All of the helices are retained and their lengths are very similar. The most-significant differences are the truncation of three helices in P-450 eryF and the repositioning of another helix (the B’ helix) in P-450.eryF such that it is perpendicular to (not co-planar with) the haem. The latter change enlarges the substrate-binding site in P-450 eryF relative to P-450cam. The actinomycetes exhibit highly variable phenotypes and express a variety of broad-specificity enzymes (such as P-450s). This may be a vital part of their survival strategy in unfavourable environments, where they must depend on diverse nutritional sources (O’Keefe and Harder, 1991). Among the P-450s characterized from bac- teria in the order Actinomycetales are enzymes catalysing alkane hydroxylation, pentachlorophenal dehalogenation and alkoxyphenol O-dealkylation from various Rhodo- coccus strains (Karlson et al., 1993 and references therein). Recently, the genes encoding a P-450 system involved
Fig. 3. Structural comparison of cytochromes P-450ery F and P-450cam. The overall topology of the bacteria! P-450 structures solved (P-450cam, P-450 BM-3 haem domain, P-450terp and P-450 eryF) is well conserved. The diagram shows a stereo view of an overlay of the structures of P-450 eryF (shaded) and P-450cam (white). All of the helices are retained and their lengths are very similar. The most-significant differences are the truncation of three helices in P-450 eryF and the repositioning of another helix (the B’ helix) in P-450.eryF such that it is perpendicular to (not co-planar with) the haem. The latter change enlarges the substrate-binding site in P-450 eryF relative to P-450cam. The actinomycetes exhibit highly variable phenotypes and express a variety of broad-specificity enzymes (such as P-450s). This may be a vital part of their survival strategy in unfavourable environments, where they must depend on diverse nutritional sources (O’Keefe and Harder, 1991). Among the P-450s characterized from bac- teria in the order Actinomycetales are enzymes catalysing alkane hydroxylation, pentachlorophenal dehalogenation and alkoxyphenol O-dealkylation from various Rhodo- coccus strains (Karlson et al., 1993 and references therein). Recently, the genes encoding a P-450 system involved
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