A single point mutation (E166Q) prevents dicyclohexylcarbodiimide binding to the photosystem II subunit CP29.
Energy-dependent quenching of chlorophyll fluorescence (qE) reflects the action of a powerful mechanism of protection from photoinhibition in which the low pH in the chloroplast lumen induces dissipation of excess excitation energy. Dicyclohexylcarbodiimide (DCCD), a protein-modifying agent, is a powerful inhibitor of qE and has been shown to react with acidic residues, in a hydrophobic environment, involved in proton translocation. The CP29 subunit of photosystem II has been proposed to be the site of qE quenching and shown to bind DCCD. We have hypothesised, on the basis of the CP29 protein sequence and of the structure of light-harvesting complex II protein, that glutamic acid 166 is the DCCD binding site. In this study, we have produced recombinant proteins either with wild-type sequence or carrying a mutation on the 166 position. We show that the mutant protein does not bind DCCD. This identifies E166 as the site whose protonation may lead to a conformational change triggering qE.
Pesaresi
P
P
Università di Verona, Facoltà di Scienze MM.FF.NN., Italy.
Sandonà
D
D
Giuffra
E
E
Bassi
R
R
D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002734:Chlorophyll / Q000378:metabolism; D003001:Cloning, Molecular; D004024:Dicyclohexylcarbodiimide / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D017354:Point Mutation; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000378:metabolism
D001059:Apoproteins; C069660:CP29 light harvesting complex; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins; D002734:Chlorophyll; D004024:Dicyclohexylcarbodiimide