Jt. Wu et al., Random mutagenesis in the large extrinsic loop E and transmembrane alpha-helix VI of the CP 47 protein of Photosystem II, PLANT MOL B, 39(2), 1999, pp. 381-386
The intrinsic chlorophyll-protein CP 47 is a component of Photosystem II wh
ich functions in both light-harvesting and oxygen evolution. Using the Esch
erichia cell mutator strain XL-I Red, we introduced mutations at 14 sites i
n the large extrinsic loop E of CP 47 and its adjacent transmembrane cu-hel
ix VI. Four mutant cell lines were recovered in which the histidyl residues
H-455, H-466 and H-469 were altered. The cell lines H455T, H455Y, H469Y, a
nd the double mutant F432L,H466R exhibited phenotypes that supported the id
entification of the histidyl residues H-455, H-466 and H-469 as chlorophyll
ligands. Four additional mutant cell lines were recovered which contained
mutations at positions R-448 in the large extrinsic loop of CP 47. These mu
tants, R448K, R338Q, R448S, and R448W, exhibited variable phenotypes rangin
g from moderate alteration of photoautotrophic growth and oxygen evolution
rates to a complete inhibition of these parameters. Those mutants exhibitin
g photoautotrophic growth and oxygen evolution capability under standard co
nditions were unable to grow photoautotrophically or evolve oxygen when gro
wn at low chloride concentrations. Finally, a mutant cell line exhibiting a
substitution at position (342)G was recovered. The mutant G342D exhibited
moderate alterations of photoautotrophic growth and oxygen evolution. In ad
dition to these alterations, mutants were recovered in which deletions and
insertions (leading to frame shifts) and stop codons were introduced. These
mutants uniformly lacked the ability to either grow photoautotrophically o
r evolve oxygen.