Ycf12 is a core subunit in the photosystem II complex

Area of Science:

• Photosynthesis research
• Protein biochemistry
• Structural biology

Background:

• Cyanobacterial photosystem II (PS II) is crucial for oxygenic photosynthesis.
• Recent crystallographic models suggest an uncharacterized low molecular weight (LMW) transmembrane component in PS II.
• The identity and role of this LMW component have remained elusive.

Purpose of the Study:

• To identify the unknown transmembrane LMW component in highly purified PS II core complexes.
• To determine the polypeptide composition of PS II from *Thermosynechococcus elongatus*.
• To assign the function and localization of the *ycf12* gene product.

Main Methods:

• Purification of intact PS II core complexes from *Thermosynechococcus elongatus*.
• Electrophoresis system optimized for separating LMW hydrophobic proteins.
• N-terminal amino acid sequencing of identified PS II components.

Main Results:

• A novel protein of approximately 5 kDa was identified as a PS II component.
• The N-terminal sequence matched that of Ycf12, a previously uncharacterized gene product.
• The *ycf12* gene is conserved in cyanobacterial and chloroplast genomes.

Conclusions:

• The study provides the first evidence that *ycf12* is expressed as a functional component of the PS II complex.
• A previously unidentified transmembrane protein, Ycf12, is part of the PS II core complex.
• This discovery advances our understanding of PS II structure and function.