UFSP1 (Q6NVU6) research notes

Identity

• Ufm1-specific protease 1, peptidase C78 family (MEROPS C78.001), paralog of UFSP2.
• Long misannotated as catalytically inactive in humans because the canonical 445AUG-initiated protein lacks the catalytic cysteine/protease domain.

Core function: active UFM1-specific cysteine protease

• Two 2022 papers established that the endogenous active UFSP1 is translated from an upstream non-canonical (near-cognate CUG/CTG ~217) start codon, producing a longer ~24 kDa isoform (A0A5F9ZGY7) that contains the catalytic Cys protease domain. PMID:35926457 PMID:35525273
• UFSP1 is an active cysteine protease that matures pro-UFM1 (removes the C-terminal Ser-Cys dipeptide to expose the C-terminal Gly) AND de-UFMylates target proteins. PMID:35525273
• Catalytic residue: Cys (ACT_SITE 45 in the short-numbered entry; C->A abolishes activity). [UniProt MUTAGEN 45 "C->A: Abolished isopeptidase activity"]

Distinct vs redundant roles (UFSP1 vs UFSP2)

• Both contribute redundantly to pro-UFM1 maturation; cells lacking both UFSPs show complete loss of UFMylation due to absence of mature UFM1. PMID:35926457
• UFSP2 (ER-localized via ODR4) removes UFM1 from ribosomal RPL26; UFSP1 does NOT reverse RPL26 UFMylation. UFSP1 acts earlier — matures UFM1 and removes a potentially autoinhibitory UFM1 modification on UFC1 (at K122). PMID:35926457
• UFSP1 is cytosolic. [UniProt "SUBCELLULAR LOCATION: Cytoplasm, cytosol"] PMID:35926457
• In vitro UFSP1 cleaves UFM1 from diverse substrates (UBA5~UFM1, UFC1~UFM1) and disassembles K69-linked polyUFM1 chains. PMID:35926457

Annotation assessment

• deUFMylase activity (GO:0071567), cysteine-type peptidase activity (GO:0008234): CORE MF, IDA-supported.
• protein maturation (GO:0051604), protein ufmylation (GO:0071569): correct BP context (pro-UFM1 maturation enables UFMylation). Process annotations; keep. ufmylation is the pathway it regulates/enables.
• cytosol (GO:0005829): correct localization, IDA + IEA.
• protein binding (GO:0005515, PMID:32296183): high-throughput IntAct interactome with ~40 partners (transcription factors etc.), uninformative; no specific functional partner. KEEP_AS_NON_CORE per guidelines.

Pathway step (batch guidance)

UFSP1/UFSP2 = UFM1-specific proteases in the UFMylation cascade (UBA5 E1, UFC1 E2, UFL1 E3, DDRGK1/UFBP1 adaptor). Core MF here is the UFM1-specific/cysteine protease (deUFMylating) activity.