Primary Structure and Expression in Escherichia coli of the Mn-stabilising Protein Involved in Photosystem II Water Oxidation

Summary

Comparison of amino acid sequences of Mn-stabilising protein (MSP) of Anacystis nidulans R2 and spinach reveals 5 clusters of conserved residues. Domains essential for the functioning of MSP are likely to be situated in these clusters. The two cysteine residues of MSP are conserved. They are likely to form a disulfide bond which plays an important role in maintaining the tertiary structure of the protein.

The precursor of the Anacystis MSP possesses an N-terminal signal peptide composed of 28 amino acid residues, the structure for translocation across the thylakoid membrane. The following has been found upon expression of the MSP gene in Escherichia coli. (I) The expression gives a polypeptide of 30 kDa, which is indistinguishable in size from the authentic mature MSP although the gene directs the precursor. (II) The 30-kDa polypeptide is located at the outer surface of the cytoplasmic membrane. These findings suggest that the precursor MSP synthesised in E. coli is processed to the mature protein by a signal peptidase of E. coli.