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Site‐Directed Mutagenesis and Analysis of Second‐Site Revertants Indicates a Requirement for C‐Terminal Amino Acids of PsaB for Stable Assembly of the Photosystem I Reaction Center Complex in Chlamydomonas reinhardtii
Author(s) -
Lee Hyeonmoo,
Bingham Scott E.,
Webber Andrew N.
Publication year - 1996
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1996.tb02420.x
Subject(s) - chlamydomonas reinhardtii , chlamydomonas , photosystem i , amino acid , thylakoid , mutant , photosynthetic reaction centre , n terminus , mutagenesis , c terminus , biology , photosystem ii , chloroplast , biophysics , chemistry , biochemistry , peptide sequence , photosynthesis , gene
The PsaA and PsaB polypeptides form the reaction center core heterodimer of photosystem I (PSI). Both PsaA and PsaB are predicted to have 11 hydrophobic domains, although it is unclear how both polypeptides fold within the thylakoid membrane. If all 11 hydrophobic regions form membrane‐spanning domains, the N‐ and C‐terminus must be located on opposite sides of the membrane. The C‐terminus of PsaB is very conserved in a wide range of organisms and may be important for PSI assembly or function. Using chloroplast transformation in Chlamydomonas reinhardtii we have generated a series of C‐terminal extension and deletion mutants of the PsaB polypeptide. Analysis of these mutants and spontaneous revertants indicates that the C‐terminus may be extended by at least 14 amino acids without impairing PSI assembly. Deletion of amino acids 732–736 also has no impact on PSI, whereas deletion of amino acids 727–736 results in no accumulation of the complex. The site of truncation in the 727–736 deletion coincides with the end of the hydrophobic domain XI supporting a location of the C‐terminus of PsaB on the lumenal side of PSI.