SecProteine

SecProteine is a proposed bacterial protein associated with the Sec protein translocation pathway. It has been identified in genome-wide surveys aimed at cataloging components linked to Sec-dependent secretion and named for its presumed connection to the Sec machinery rather than a fully established function. In multiple species, SecProteine homologs share a small, acidic core and a predicted signal peptide, suggesting export into the periplasm or cell wall–adjacent spaces.

Structure and localization: SecProteine is predicted to be about 15–20 kDa after signal peptide removal. It generally lacks transmembrane segments, pointing to a soluble periplasmic localization in Gram-negative bacteria or a secreted, extracellular-facing location in Gram-positive organisms. Some variants possess conserved cysteines that may form disulfide bonds, stabilizing the protein in oxidizing environments.

Function and interactions: The proposed role of SecProteine is as a chaperone or adaptor that aids nascent secretory substrates in engaging the SecYEG complex and SecA during translocation. It may help maintain substrates in an export-competent state or assist in early folding steps near the translocon. Experimental evidence is limited, and observed phenotypes in knockout strains are often modest and context-dependent, indicating that SecProteine is nonessential in many backgrounds or redundant with other factors.

Genomic context and evolution: SecProteine genes are sometimes located near secA or secY operons and show a patchy distribution across bacteria, consistent with lineage-specific retention and occasional horizontal transfer. Comparative analyses reveal varying degrees of sequence conservation, concentrated in certain phyla.

Significance: If confirmed, SecProteine could refine models of Sec export and represent a potential target in pathogens where it plays a stabilizing role for secreted proteins. Further biochemical and structural studies are required to define its mechanism and substrate range.