Plant peroxidases superfamilies

Fig. 6. Mechanisms for the reduction of compounds I and II of HRP C by ferulic acid, after Henriksen et al. 195). This scheme is based on new information from the 1.45 A resolution crystal structure of the ternary complex of ferulic acid and cyanide-ligated HRP C 195). The direction of proton transfer is indicated by the dotted arrows. The mechanism is discussed in Section IV,B,2, and the crystal structure data in Section IV,F,4. Note that a distal site water molecule makes an important hydrogen bond with the backbone carbonyl group of Prol39 (a residue conserved in all members of the plant peroxidase superfamily).

Welinder KG (1991) Bacterial catalase-peroxidases are gene duplicated members of the plant peroxidase superfamily. Biochim Biophys Acta 1080 215-220... 

Peroxidases fall into two superfamilies (plant and mammalian) and a third, indistinct group that includes chloroperoxidase (a P450-like hybrid) and di-heme cytochrome c peroxidase from Pseudomonas aeruginosa. The plant peroxidase superfamily contains enzymes of plant, fungal, and bacterial origin [126], Mammalian peroxidases make up the second superfamily, and include lactoperoxidase, myeloperoxidase, and prostaglandin H synthase. Both families have been the focus of numerous excellent reviews, several of which have discussed the differences between the plant and mammalian peroxidases [126-130], Here, recent experimental investigations focused on the plant peroxidases will be discussed. 

The plant peroxidase superfamily consists of evolutionarily related heme peroxidases from bacteria, fungi, and plants (28). The superfamily can be divided into three classes based on amino acid sequence (28). CCP and plant cytosolic ascorbate peroxidase fall into class I, and the main role of peroxidases in this class appears to be the removal of H2O2. Class II comprises the extracellular peroxidases such as lignindegrading LIP and MnP CIP and ARP also belong to class II, but their function is unknown. Class III peroxidases include the classical plant secretory peroxidases such as HRP and its isoenzymes, and barley peroxidase. 

Although there is little overall sequence homology within the plant peroxidase superfamily, the tertiary structures obtained to date (CCP, LIP, ARP, and CIP), display considerable structural similarity. All possess 10 major a-helices (A-J) and little )8-structure. The connecting loops between the helices vary greatly in length, and LIP, ARP, and CIP have 50 additional residues at what corresponds to the C-terminal of CCP, which has 294 residues. CCP and other class I peroxidases do not contain the four disulfide bridges, the two structural Ca ions, or the glycosylation sites found in class II and III peroxidases. Neither... 

There are nine invariant residues in the plant peroxidase superfamily 28). Five of these are involved in catalysis and are shown in Fig. 2 for CCP. The other conserved residues play important structural roles, such as a buried salt bridge between AsplOG and Argl30 (CCP numbering) 28). 

As with the plant peroxidase superfamily and other families of homologous enzymes 27, 28), it is to be anticipated that the 3D structures of the mammalian peroxidases will be shown to be very similar. A comparison of the sequences of MPO, TPO, EPO, and LPO reveals that the residues surrounding the heme are highly conserved (7, 14), suggesting a common heme environment for these four mammalian peroxidases. Furthermore, all 12 cysteines involved in the six disulfide bridges in MPO (Fig. 7) are conserved in the four mammalian peroxidases. Thus, if the pattern of disulfide bonds seen in MPO is also conserved, the 3D structures are likely to be very similar 14). 

Similar mechanisms of compound I formation are believed to hold for plant and fungal peroxidases. Five of the nine conserved residues in the plant peroxidase superfamily (Section II,G) are at the active site, and these residues in CCP (Arg48, His52, Asn82, Hisl75, Asp235) are shown in Fig. 2. Elucidation of the X-ray structures of LIP (Fig. 

Recently however, a basic peroxidase, anhydrovinblastine synthase, which couples eatharanthine and vindoline to yield anhydrovinblastine, the putative precursor to vinblastine and vincristine, has been purified and characterized from C. roseus leaves 421,422). The enzyme showed a specifie anhydrovinblastine synthase activity of l.Snkatmg and a molecular weight of 45.40kDa. It was shown to be a high-spin ferrie heme protein belonging to the plant peroxidases superfamily (class HI peroxidases), and eytochemical studies showed that the enzyme is localized in the mesophyll vacuoles, in individual spots at the inner surface of the tonoplast. On the basis of the ability of the monomeric alkaloid substrates to reduce the C. roseus basic... 

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