Translocon-associated protein subunit gamma

Translocon-associated protein subunit gamma (TRAP-gamma, encoded by SSR3) is a 21 kDa component of the TRAP complex localised to the endoplasmic reticulum membrane (UniProt: Q9UNL2). The protein functions in calcium binding to the ER membrane, a process essential for regulating the retention of ER-resident proteins and maintaining proper endoplasmic reticulum homeostasis.

TRAP-gamma is part of the broader translocon machinery involved in protein translocation and ER quality control. These processes are fundamental to cellular proteostasis and have relevance to neurodegenerative conditions characterised by protein misfolding and accumulation (UniProt: Q9UNL2).

In Alzheimer's disease, SSR3 is significantly upregulated in post-mortem brain tissue compared to age-matched controls, with a mean log2 fold-change of +1.01 (Chaparral AD proteomics). This upregulation was detected across subcellular fractions in TMT-labelled proteomics of the P2, P3, S2, and S3 fractions, suggesting a potential compensatory response to ER stress or impaired protein quality control mechanisms associated with AD pathology.