Structure-function studies on the interaction of PsaC with the Photosystem 1 heterodimer

Abstract

The interaction of PsaC with the core heterodimer of Photosystem 1 was studied in wild type Synechocystis sp. PCC 6803 and the site-directed mutant R561E of PsaB. The mutant reaction center was much less stable in urea and the functional reconstitution of the mutant core using PsaC was impaired. However, the extent of reconstitution increased in the presence of divalent cations whereas that of the wild type was inhibited. We conclude that the reaction center in the mutant is unstable, most likely due to the introduction of an unfavorable electrostatic interaction between surface-exposed residues on PsaC and the binding site for the subunit on the core heterodimer in support of the model proposed previously (Rodday et al. (1993) Photosynth Res 36: 1-9).

Introduction of a [4Fe‐4S (S‐cys)4]+1,+2 iron‐sulfur center into a four‐α helix protein using design parameters from the domain of the Fx cluster in the Photosystem I reaction center

“…We suggest that coordination of the [4Fe-4S (S-cys)4] cluster into this protein backbone supports the predictions that have been made regarding the organization of the four cysteine ligands for the native Fx cluster in the PS I core (Golbeck, 1993;Rodday et al, 1993Rodday et al, , 1994. However, we also suggest that the specific intercysteinyl sequence we used for modification of loops 1 and 3 of a4, patterned after the Fx domain, is not essential for cluster insertion per se, and possibly two or three connecting glycine residues would suffice.…”

“…The four cysteine ligands for coordination of the Fx cluster reside on two identical interhelical loops, PCDG-PGRGGTC, between helices Vlll and 1X of each PS I core subunit, and we suggested that the loops at the apex of the four-a helix bundle could form a surface-exposed cavity and contribute in the binding of the PsaC subunit (see Figure 1 of Rodday et al, 1993). The working model has been supported experimentally by chemical modification procedures and site-directed mutagenesis of key residues in the Fx loops of the PsaA/PsaB core subunits (Rodday et al, 1993(Rodday et al, , 1994Hallahan et al, 1995) and PsaC Rodday et al, 1996).…”

Photosystem I, an Improved Model of the Stromal Subunits PsaC, PsaD, and PsaE

“…It is therefore likely that some amino acids of these strands interact with the water-soluble electron acceptors. The mutation of Arg 39 to Gln (R39Q) at the C terminus of the strand ␤C is known to partly inhibit ferredoxin reduction (28), an observation that is corroborated by the structural model. The shortest distance between PsaE and the loop w-x and ␣-helix u (PsaF, PsaJ, and PsaM; see below) are ϳ12 and ϳ20 Å, respectively (Fig.…”

“…The intercysteine loops of this motif have been suggested to play a leading role in binding the extrinsic subunit PsaC (39,40). In particular, one of the central arginines of the F X -binding motifs (boldface R in the sequence motif) was postulated to form a salt bridge with an aspartate of PsaC and consequently to be crucial in determining the orientation of this subunit (41).…”

Reconstitution of Barley Photosystem I with Modified PSI-C Allows Identification of Domains Interacting with PSI-D and PSI-A/B

“…17 and 19); therefore, the binding activity of the loop must involve interaction with PSI-A and PSI-B. Studies of Rodday et al (36,37) suggest that arginine residues in the conserved domain in PSI-A and PSI-B that binds F X are important for the interaction with PSI-C. The 8-residue internal loop contains two negative charges that may be responsible for the specific interaction with the arginines.…”