8.A.191. The Translocon-associated Protein Subunit beta (TPSβ) Family The translocon-associated protein (TRAP) subunit, beta (TPSβ) family includes the SSR2 protein of 183 aas and 2 TMSs at the N- and C-termini of the protein. TRAP proteins are parts of a complex whose function is to bind calcium to the ER membrane and thereby regulate the retention of ER resident proteins. It is an SRP-dependent cotranslational protein, targeting its substrates to the membrane (Chen et al. 2022). Signal Sequence Receptor Subunit 2 (SSR2) is a key endoplasmic reticulum gene involved in protein folding and processing. It is upregulated in several cancers, and the expression of the SSR2 gene in hepatocellular carcinoma (HCC) tissues has been noted. The expression of SSR2 is increased in HCC tissues, and SSR2 expression is associated with several clinical characteristics. SSR2 is probably involved in signalling pathways related to the G2/M checkpoint, passive transmembrane transporter activity, and ncRNA metabolic process. SSR2 knockdown inhibits cell proliferation, migration and invasive ability and promoted apoptosis and cell cycle arrest in vitro. Moreover, downregulation of SSR2 also repressed the growth of HepG2 cells in vivo, suggesting that the SSR2 gene is an oncogene in HCC (Chen et al. 2022).
References:
Chen, F., Chen, J. Wang, S. Zhang, M. Chen, X. Zhang, and Z. Wu. (2022). Overexpression of SSR2 promotes proliferation of liver cancer cells and predicts prognosis of patients with hepatocellular carcinoma. J Cell Mol Med. [Epub: Ahead of Print]
Examples:
TC#	Name	Organismal Type	Example
8.A.191.1.1	TRAP proteins are parts of complexes whose function is to bind calcium to the ER membrane and thereby regulate the retention of ER resident proteins. SSR2 is also an oncogene (see family description).		SSR2 of Homo sapiens

8.A.191.1.2	Translocon-associated protein beta subunit, SSR2, of 191 aas and 2 TMSs, N- and C-teminal.		SSR2 of Zostera marina

8.A.191.1.3	Uncharacterized protein of 229 aas and 2 or 3 TMSs, with one N-terminal, one C-terminal, and possibly one centrally located.		UP of Haematococcus lacustris

8.A.191.1.4	Uncharacterized protein of 229 aas and 2 or 3 TMSs, one N-terminal, one C-terminal and possibly one centrally located.		UP of Pelomyxa schiedti

8.A.191.1.5	Uncharacterized protein of 283 aas and 2 - 4 TMSs, one N-terminal, one C-terminal and up to 2 more centrally located.		UP of Folsomia candida

8.A.191.1.6	Translocon-associated protein beta-domain-containing protein, SSR2, of 198 aas and two TMSs, N- and C-terminal, possibly plus one of two more,centrally located.		SSR2 of Blyttiomyces helicus

8.A.191.1.7	Translocon-associated protein beta (TRAPB) of 189 aas and 2 TMSs, N- and C-terminal.		TRAPB of Monocercomonoides exilis

8.A.191.1.8	Uncharacterized protein of 597 aas with a C-terminal domain homologous to the members of this family. This domain is flanked by two TMSs. It may be a partial sequence.		UP of Auxenochlorella protothecoides

8.A.191.1.9	Uncharacterized protein of 517 aas and a C-terminal domain homolgous to members of this family. The protein has two certain TMSs at its extreme N-terminus and its extreme C-terminus, as well as one or two fairly hydrophobic TMS in the region of residues 360 - 410.		UP of an ANME-2 cluster archaeon