Identification of Functional Domains of PsbU in Red Algal PSII by Site-Directed Mutagenesis

Abstract

In Order To Determine The Functional Domain(S) Of The Extrinsic 12 Kda Protein (Psbu) In Red Algal Photosystem Ii (Psii), We Prepared Various Mutants Of Psbu And Reconstituted The Mutant Psbu With Red Algal Psii Retaining The 33 Kda (Psbo), 20 Kda (Psbq) And Cyt C550 (Psbv). (1) Analysis Of Oxygen-Evolving Activities In The Absence Or Presence Of Nacl And Cacl2 Of The Reconstituted Psii Revealed That Tyrosine-92 (Y92) Of The Second Residue From The C-Terminus Of Psbu Was Important For Its Function To Optimize The Availability Of Chloride And Calcium Cofactors For Water Oxidation. (2) In Order To Determine The Function Of Y92, We Constructed A Series Of Mutants By Replacing Y92 With Various Amino Acids. Substitution Of Y92 With Threonine, Asparatic Acid, Arginine Or Isoleucine Totally Abolished The Function Of Psbu. In Contrast, Substitution Of Y92 With Phenylalanine Retained The Function Of Psbu. These Results Indicate That Aromatic Structure Of Y92 In Psbu Is Important For Maintaining Its Functional Structure.