N-bromosuccinimide modification of tryptophan 241 at the C-terminus of themanganese stabilizing protein of plant photosystem II influences its structure and function

Life on earth depends upon the ability of oxygenic photosynthesis to oxidiz e water to molecular oxygen, This process is catalyzed by water-plastoquino ne oxido-reductase complex, In addition to the photosystem II (PSII) reacti on core, it includes a manganese stabilizing protein (MSP) that plays an im portant regulatory role in the process in plants and algae, Tryptophan 241, located at the carboxyl-terminus of the MSP, is its: sole tryptophan. Modi fication of MSP by N-bromosuccinimide (NBS) was carried out to explore the role of Trp241 in maintaining its structure and function. Data and argument s are presented to show that it is Trp241, not other tyrosines in MSP, that is involved in the modification and changes observed in this study, Furthe r, the pH-dependence of the modification and the comparison of features of fluorescence spectra of MSP suggested that Trp241 is buried in the hydropho bic interior of the protein. Hydropathy analysis revealed that Trp241 is lo cated in the middle of the hyrophobic region at the C-terminus of MSP. Circ ular dichroism spectroscopy showed that NBS modification of Trp241 dramatic ally modified the protein structure, The affinity of MSP to PSII decreased greatly after the modification of Trp241, and no oxygen-evolving activity w as recovered after its reconstitution. This study provides a novel demonstr ation that Trp241 at the C-terminus hydrophobic region of the MSP is critic al for maintaining appropriate structure and function of MSP.