SRP72

SRP72 is a 72-kilodalton protein subunit of the eukaryotic signal recognition particle (SRP). It forms a heterodimer with SRP68, and together the SRP68/72 complex is part of the SRP’s cytosolic S-domain that participates in recognizing signal sequences and targeting ribosome–nascent chain complexes to the endoplasmic reticulum (ER). The SRP itself is a ribonucleoprotein particle composed of the 7SL RNA and multiple protein components, including SRP9/14, SRP19, SRP54, and the SRP68/72 heterodimer.

Functionally, SRP72 contributes to the assembly and stabilization of the SRP and plays a role in the co-translational targeting pathway. As a ribosome–nascent chain emerges from the ribosome, the SRP recognizes the signal peptide, pauses translation via the SRP54 GTPase, and delivers the complex to the SRP receptor on the ER membrane. The SRP68/72 heterodimer aids docking and proper interaction with the receptor, facilitating efficient transfer of the translating ribosome to the translocon for protein insertion or translocation.

Localization and evolution: SRP72 is conserved across eukaryotes and is primarily cytosolic, associating with the ER membrane during active targeting. It is broadly expressed in cells that synthesize secretory and membrane proteins.

Genetics and clinical notes: SRP72 is encoded by the SRP72 gene and is considered essential for normal SRP function and cell viability. Alterations in SRP72 expression or sequence have been studied in the context of human disease, reflecting the broader importance of SRP components in protein targeting and cellular homeostasis.