 |
|
Title
|
|
Solution structure of reduced plastocyanin from the blue-green alga Anabaena variabilis.
|
|
|
Authors
|
|
U.Badsberg,
A.M.Jørgensen,
H.Gesmar,
J.J.Led,
J.M.Hammerstad,
L.L.Jespersen,
J.Ulstrup.
|
|
|
Ref.
|
|
Biochemistry, 1996,
35,
7021-7031.
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
The three-dimensional solution structure of plastocyanin from Anabaena
variabilis (A.v.PCu) has been determined by nuclear magnetic resonance
spectroscopy. Sixty structures were calculated by distance geometry from 1141
distance restraints and 46 dihedral angle restraints. The distance geometry
structures were optimized by simulated annealing and restrained energy
minimization. The average rms deviation from the mean structure for the 20
structures with the lowest total energy is 1.25 A for the backbone atoms and
1.75 A for all heavy atoms. Overall, the global tertiary fold of A.v.PCu
resembles those of other plastocyanins which have been structurally
characterized by X-ray diffraction and NMR methods. This holds even though
A.v.PCu is longer than any other known plastocyanins, contains far less
invariant amino acid residues, and has an overall charge that differs
considerably from those of other plastocyanins (+1 vs -9 +/- 1 at pH > or =
7). The most striking feature of the A.v. PCu structure is the absence of the
beta-turn, formed at the remote site by residues (58)-(61) in most higher plant
plastocyanins. The displacement caused by the absence of this turn is
compensated for by an extension of the small helix [from Ala53(51) to Ser60(58)
in A.v.PCu] found in other plastocyanins. Moreover, the extra residues of
A.v.PCu from Pro77 to Asp79 form an appended loop. These two features allow
A.v.PCu to retain almost the same global fold as observed in other
plastocyanins. From a comparison with the structures of other plastocyanins it
is concluded that the lack of negatively charged residues at the remote site,
rather than the specific structure of A.v.PCu, is the main reason for the
failure of the remote site of this plastocyanin to function as a significant
electron transfer site.
|
|
|
|