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Title: N-terminal lipid modification is required for the stable accumulation of CyanoQ in Synechocystis sp. PCC 6803

Here, the CyanoQ protein has been demonstrated to be a component of cyanobacterial Photosystem II (PS II), but there exist a number of outstanding questions concerning its physical association with the complex. CyanoQ is a lipoprotein; upon cleavage of its transit peptide by Signal Peptidase II, which targets delivery of the mature protein to the thylakoid lumenal space, the N-terminal cysteinyl residue is lipid-modified. This modification appears to tether this otherwise soluble component to the thylakoid membrane. To probe the functional significance of the lipid anchor, mutants of the CyanoQ protein have been generated in Synechocystis sp. PCC 6803 to eliminate the N-terminal cysteinyl residue, preventing lipid modification. Substitution of the N-terminal cysteinyl residue with serine (Q-C22S) resulted in a decrease in the amount of detectable CyanoQ protein to 17% that of the wild-type protein. Moreover, the physical properties of the accumulated Q-C22S protein were consistent with altered processing of the CyanoQ precursor. The Q-C22S protein was shifted to a higher apparent molecular mass and partitioned in the hydrophobic phase in TX-114 phase-partitioning experiments. These results suggest that the hydrophobic N-terminal 22 amino acids were not properly cleaved by a signal peptidase. Substitution of the entire CyanoQ transit peptide withmore » the transit peptide of the soluble lumenal protein PsbO yielded the Q-SS mutant and resulted in no detectable accumulation of the modified CyanoQ protein. Finally, the CyanoQ protein was present at normal amounts in the PS II mutant strains ΔpsbB and ΔpsbO, indicating that an association with PS II was not a prerequisite for stable CyanoQ accumulation. Together these results indicate that CyanoQ accumulation in Synechocystis sp. PCC 6803 depends on the presence of the N-terminal lipid anchor, but not on the association of CyanoQ with the PS II complex.« less
 [1] ;  [1] ;  [1] ;  [1] ;  [2]
  1. Louisiana State Univ., Baton Rouge, LA (United States)
  2. Univ. of California, Davis, CA (United States)
Publication Date:
Grant/Contract Number:
FG02-98ER20310; FG02-09ER20310; FG02-09ER16070; SC0002628
Published Article
Journal Name:
Additional Journal Information:
Journal Volume: 11; Journal Issue: 9; Journal ID: ISSN 1932-6203
Public Library of Science
Research Org:
Louisiana State Univ., Baton Rouge, LA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; lipids; signal peptides; peripheral membrane proteins; synechocystis; signal processing; proteases; membrane proteins; outer membrane proteins; 60 APPLIED LIFE SCIENCES; Peripheral Membranes; Synchocystis
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1361695; OSTI ID: 1393395