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Endogenous interactors of the natural trapping mutant TMX5/TXNDC15

ABSTRACT: The endoplasmic reticulum (ER) is the organelle of nucleated cells that produces lipids, sugars and proteins. More than 20 ER-resident members of the Protein Disulfide Isomerase (PDI) family regulate formation, isomerization and disassembly of covalent bonds in newly synthesized polypeptides. The PDI family includes few membrane-bound members. Among these, TMX1, TMX2, TMX3, TMX4 and TMX5 belong to the thioredoxin-related transmembrane (TMX) protein family. TMX5 is the least known member of the family. Here, we establish that TMX5 covalently engages via its active site cysteine residue at position 220 a subset of secretory proteins, mainly single- and multi-pass Golgi-resident polypeptides. TMX5 also interacts non-covalently, and covalently, via non-catalytic cysteine residues, with the PDI family members PDI, ERp57 and ERp44. The association of TMX5 and ERp44 requires formation of a mixed disulfide between the catalytic cysteine residue 29 of ERp44 and the non-catalytic cysteine residues 114 and/or 124 of TMX5 and controls the ER retention of TMX5. Thus, TMX5 belongs to the family of proteins including Ero1, Ero1, Prx4, ERAP1, SUMF1 that do not display ER retention sequences and rely on ERp44 engagement for proper inter-compartmental distribution. The client-specificity of TMX5 in cellulo was assessed by expressing mutant forms of the enzymes, where the last cysteine residue of the TMX’s CXXC catalytic sites has been mutated to alanine, which stabilizes the mixed disulfide that oxidoreductases establish with clients. Clients remain disulfide-bonded to the oxidoreductase and are identified upon co-immunoprecipitation and mass spectrometry analyses.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Hek-293t Cell

SUBMITTER: Manfredo Quadroni

LAB HEAD: Maurizio Molinari

PROVIDER: PXD054716 | Pride | 2024-09-27

REPOSITORIES: Pride

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Project description:Pharmacological activation of the activating transcription factor 6 (ATF6) arm of the Unfolded Protein Response (UPR) has proven useful for ameliorating proteostasis deficiencies in a variety of etiologically diverse diseases. Previous high-throughput screening efforts identified the small molecule AA147 as a potent and selective ATF6 activating compound that operates through a mechanism involving metabolic activation of its 2-amino- p -cresol substructure affording a quinone methide, which then covalently modifies a subset of ER protein disulfide isomerases (PDIs). Intriguingly, another compound identified in this screen, AA132, also contains a 2-amino- p -cresol moiety; however, this compound showed less transcriptional selectivity, instead globally activating all three arms of the UPR. Here, we show that AA132 activates global UPR signaling through a mechanism analogous to that of AA147, involving metabolic activation and covalent PDI modification. Chemoproteomic-enabled analyses show that AA132 covalently modifies PDIs to a greater extent than AA147. Paradoxically, activated AA132 reacts slower with PDIs, indicating it is less reactive than activated AA147. This suggests that the higher labeling of PDIs observed with activated AA132 can be attributed to its lower reactivity, which allows this activated compound to persist longer in the cellular environment prior to quenching by endogenous nucleophiles. Collectively, these results suggest that AA132 globally activates the UPR through increased engagement of ER PDIs. Consistent with this, reducing the cellular concentration of AA132 decreases PDI modifications and allows for selective ATF6 activation. Our results highlight the relationship between metabolically activatable-electrophile stability, ER proteome reactivity, and the transcriptional response observed with the enaminone chemotype of ER proteostasis regulators, enabling continued development of next-generation ATF6 activating compounds.

			Action	DRS
	190611_Molinari_11392-NR.raw	Raw
	190611_Molinari_11392-R.raw	Raw
	F015987.dat	Other
	F015987.mgf	Mgf
	F015987.mzid.gz	Mzid

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Endogenous interactors of the natural trapping mutant TMX5/TXNDC15

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