Plastocyanin amino-acid sequence

Fig. 3. Plastocyanin amino-acid sequences relevant to this review. Other sequence information is included. There are now 24 known sequences (18 formerly in Ref. [ I]). The 23 residues invariant throughout all 24 known higher plant and algal plastocyanin sequences are indicated ( ), 5 others (A) are invariant if A. variabilis is excluded, and a further 19 (o) if only the higher plant sequences are considered. Eieletions are indicated ( ), and residues which coordinate the Cu(V)...

From 13 completed amino-acid sequences and 54 partial sequences (>40 residues) of plastocyanins from higher plants it appears that sixty residues are invariant and 7 are conservatively substituted 02,7). With three algal plastocyanins included there are 39 invariant or conservatively substituted groups. It is believed that the same structural features apply to the whole family, and that highly conserved residues are an indication of functional sites on the protein surface. The upper hydrophobic and right-hand-side surfaces are believed to be particularly relevant in this context, the latter including four consecutive... 

It is interesting to note that the plastocyanin from the alga Anabaena variabilis has a similar structure to that isolated from poplar, while having a different amino acid sequence.58 This results in an overall positive charge of +2. Thus, as shown in Figure 32a, it affords a wellshaped response for the Cu(II)/Cu(I) reduction E° = + 0.32 V vs. NHE) using a perpendicular pyrolytic graphite electrode, without the presence of additives. 

Amino acid sequence data for many plastocyanins are now available. A large number of residues are conserved,910 particularly among the plastocyanins from higher plants, where about 50% of the residues are the same. Residues 31-44 and 84-93 are highly conserved in all the proteins, and provide the donor groups for copper. 

The azurins are electron-transfer proteins in the respiratory chains of certain bacteria. They have been particularly well studied from Pseudomonas aeruginosa and other pseudomonads, and contain one type 1 copper bound to a single polypeptide chain of molecular weight about 16 000. Amino acid sequence data for a number of azurins show that about one third of residues are conserved. All contain three cysteine residues. Three are also sequence homologies with the plastocyanins. 

Redox potentials for the different copper centers in the blue oxidases have been determined for all members of the group but in each case only for a limited number of species. The available data are summarized in Table VI 120, 121). The redox potentials for the type-1 copper of tree laccase and ascorbate oxidase are in the range of 330-400 mV and comparable to the values determined for the small blue copper proteins plastocyanin, azurin, and cucumber basic protein (for redox potentials of small blue copper proteins, see the review of Sykes 122)). The high potential for the fungal Polyporus laccase is probably due to a leucine or phenylalanine residue at the fourth coordination position, which has been observed in the amino-acid sequences of fungal laccases from other species (see Table IV and Section V.B). Two different redox potentials for the type-1 copper were observed for human ceruloplasmin 105). The 490-mV potential can be assigned to the two type-1 copper sites with methionine ligand and the 580-mV potential to the type-1 center with the isosteric leucine at this position (see Section V.B). The... 

Fic, 4. The polypeptide chain folding of Alcaligenes denitrificans azurin. Solid circles are residues inserted for comparison with plastocyanin. Probable H bonds are shown by dotted lines. Strands of /3 structures are numbered according to their positions in the amino acid sequence the inserted flap 52-81 contains an a-helix section that is seen on the right-hand side in Fig. 5. The cross-hatched circle denotes the position of the Cu atom. (Reproduced with permission from Ref S.)... 

Fig. 14. Comparison of the amino acid sequences of plastocyanin (pcy), amicyanin (acy), and pseudoazurin (paz). The copper ligands are framed conserved residues are underlined. Based on Guss and Freeman 1983 [22], Ryden and Hunt 1993 [71], and Durley et al. 1994 [78]...

The central copper ion of the auracyanins is probably coordinated by two histidines, one cysteine, and a methionine residue. The auracyanins are unique among the small blue proteins in that they possess a methionine and a glutamine residue (see phytocyanins) which both could act as the fourth ligand coordinating the central copper ion. This copper center is surrounded by a hydro-phobic environment similar to that of the other small blue proteins [68]. Amino acid sequence comparisons place auracyanin in a phylogenetic tree at approximately equal distances from azurin and plastocyanin [68,92]. 

Borthwick, J., C.J.W. Brooks, W.W. Reid, and R.A. Russell Phytochemistry of the genus Nicotiana. Part VI. A preliminary GC/MS study of some diterpenes and sterols Ann. Tabac SEITA 12 (Sect.2) (1975) 22-25. Boulter, D., D. Peacock, A. Guise, J.T. Gleavest, and G. Estabrook Relationships between the partial amino acid sequences of plastocyanine members of ten families of flowering plants Phytochemistry 18 (1979) 603-608. Brady, U.E. and D.A. Nordlund Cis-9-trans-12-tetradecadien-l-yl acetate in the female tobacco moth Ephestia elutella (Hiibner) and evidence for an additional component of the sex pheromone Life Sci. 10 (1971) 797-801. 

The distribution of tm for 6 = 170 (P) and 8 = 100 (ot) is shown in Fig. 1 for selected members of the families of chloroplastic precursors. The amino acid sequences of the transit peptides are shown in the bottom panel. The plots are aligned according to the cleavage site at the end of the transit peptide. Proteins destined for the thyla-koid lumen (i.e., plastocyanin and the polypeptides of the oxygen evolving complex) must traverse the thylakoid membrane in addition to the envelope membranes. For these precursors, the first 40-60 amino acids comprise the stromal targeting domain, whereas the last 20-25 residues form the thylakoid transport domain (9). Thus, it is the first domain that is relevant for comparison with the other transit peptides. 

A transit peptide consisting of a hydrophobic 66 amino acid long peptide interspersed with positively charged residues has been identified and sequenced [52]. This is initially attached to the 99 amino acids of the mature plastocyanin, and is responsible for taking the plastocyanin across membranes into the thylakoid region of the chloroplast. 

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