The negatively charged amino acids in the lumenal loop influence the pigment binding and conformation of the major light-harvesting chlorophyll a/b complex of photosystem II.
The major chlorophyll (Chl) a/b complexes of photosystem II (LHCIIb), in addition to their primary light-harvesting function, play key roles in the organization of the granal ultrastructure of the thylakoid membranes and in various regulatory processes. These functions depend on the structural stability and flexibility of the complexes. The lumenal side of LHCIIb is exposed to broadly variable pH environments, due to the build-up and decay of the pH gradient during photosynthesis. Therefore, the negatively charged amino acids in the lumenal loop might be of paramount importance for adjusting the structure and functions of LHCIIb. In order to clarify the structural roles of these residues, we investigated the pigment stoichiometries, absorption, linear and circular dichroism spectra of the reconstituted LHCIIb complexes, in which the negatively charged amino acids in the lumenal loop were exchanged to neutral ones (E94G, E107V and D111V). The mutations influenced the pigment binding and the molecular architecture of the complexes. Exchanging E94 to G destabilized the 3(10) helix in the lumenal loop structure and led to an acquired pH sensitivity of the LHCIIb structure. We conclude that these amino acids are important not only for pigment binding in the complexes, but also in stabilizing the conformation of LHCIIb at different pHs.
Yang
Chunhong
C
Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, PR China. yangch@ibcas.ac.cn
Lambrev
Petar
P
Chen
Zhi
Z
Jávorfi
Tamás
T
Kiss
Anett Z
AZ
Paulsen
Harald
H
Garab
Gyozo
G
D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D008968:Molecular Conformation; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010860:Pigments, Biological / Q000378:metabolism*; D011485:Protein Binding
D000596:Amino Acids; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D002734:Chlorophyll