PsbSeiwit

PsbSeiwit is a proposed, hypothetical protein associated with photosystem II (PSII) in cyanobacteria and some algae. The name is derived from standard psb gene nomenclature used for PSII subunits and a provisional suffix used by researchers proposing newly detected components.

It originated in discussions of uncharacterized open reading frames located near core psbA and psbD gene clusters in genome-resolved datasets. The designation PsbSeiwit has not been universally adopted and remains informal in most reports.

In silico analyses predict PsbSeiwit as a small, soluble protein of roughly 8–15 kDa with no predicted transmembrane segment, implying a peripheral association with the PSII core complex rather than an integral membrane component. Co-purification with PSII cores in some datasets suggests a stable, albeit weak, interaction with core subunits.

Proposed roles for PsbSeiwit include stabilization of PSII assembly intermediates, participation in repair cycles after photodamage, or modulation of PSII activity under stress conditions. However, there is currently no experimental validation of its presence, localization, or function.

Reported observations of PsbSeiwit-like sequences come from a limited set of cyanobacterial genomes. It is not known whether the protein is present across broader photosynthetic lineages or restricted to particular clades. As a hypothetical component, it is not included in standard reference catalogs of PSII subunits.

Further work, including targeted proteomics and genetic studies, would be required to establish whether PsbSeiwit is a bona fide PSII subunit and to define its role in photosynthetic biology.