Low‐molecular‐mass proteins in cyanobacterial photosystem II: Identification ofpsbH andpsbK gene products by N‐terminal sequencing

Abstract

The O,-evolving photosystem II core complex was isolated from a thermophilic cyanobacterium, Synechococcus vulcanus Copeland. Analysis by SDS-polyacrylamide gel electrophoresis revealed that the complex contained at least seven lowmolecular-mass proteins in addition to the well characterized CP47 apoprotein, CP43 apoprotein, 33 kDa extrinsic protein, Dl protein, D2 protein and large subunit of cytochrome b-559. The separation profiles of these low-molecular-mass proteins were very similar between cyanobacterial and higher plant PS II. N-terminal sequences of the 6.5 kDa and 3.9 kDa proteins of cyanobacterial core complex were determined after blotting to a polyvinylidene difluoride membrane. The sequence of the 6.5 kDa protein showed high homology with an internal sequence of plant psbH gene product, socalled 10 kDa phosphoprotein, but did not conserve the Thr residue which is specifically phosphorylated in plants. The sequence of the 3.9 kDa protein corresponded to the K protein of higher plants (mature form of psbK gene product). These results indicate that the products of both psbH and psbK genes are present in cyanobacterial PS II as well as being associated with the O,-evolving core complex.

N‐terminal sequencing of low‐molecular‐mass components in cyanobacterial photosystem II core complex Two components correspond to unidentified open reading frames of plant chloroplast DNA

“…This pattern is almost identical with our previously reported profile [10], except for the absence of a minor band of 4.4 kDa. In many cases, the 4.4 kDa protein was not recovered in OE-eVolving core complex and may well be no real PS II component.…”

“…In the previous paper, we reported that the O2-evolving PS II core complex of Synechococcus vulcanus contains many low-molecular-mass components like higher plants, and confirmed the presence of the psbH and psbK gene products by N-terminal sequencing [10]. We also detected the gene products ofpsbI and psbL as well as psbE and psbF in the cyanobacterial reaction center complex [11].…”

“…In many cases, the 4.4 kDa protein was not recovered in OE-eVolving core complex and may well be no real PS II component. As noted in fig.l, many of the bands have been identified by N-terminal sequencing as gene products of psbE, psbH, psbF, psbI, psbL and psbK [10,11] as well as atpH (unpublished). Hence, two bands, at 4.7 and 4.1 kDa, remain to be characterized.…”

“…Copeland by treatment with Triton X-100 followed by DEAEToyopearl column chromatography as in [10]. Low-molecularmass proteins were resolved by SDS-PAGE with 7.5 M urea and a 16-22% (w/v) acrylamide gradient according to [2].…”

Identification of photosystem I components from the cyanobacterium, Synechococcus vulcanus by N‐terminal sequencing

“…This method enabled discrete detection of many lowmolecular-mass components in the PS II complex [23][24][25], which could not be resolved by conventional SDS-PAGE, The resolved proteins were electroblotted to PVDF ~membrane, and directly subjected to amino acid Sequencing. By use of this method, the N-terminhl partial amino acid sequences of many new PS II components have been determined [24][25][26] ....…”