A 2024 system-wide analysis of human lipid transfer proteins (Titeca et al.) included SCP2D1 among LTPs with no previously known ligands and mapped multiple lipid-class associations (fatty acids, LPC, LPE, LPG, PE, and PG/BMP), giving the first broad biochemical handle on its potential function as a multi-class lipid-binding protein.

"In the cropped figure region, SCP2D1 is shown with ligand-class associations including"

Functional inference from the LTP ligand mapping: SCP2D1 likely binds free fatty acids and several lysophospholipid/glycerophospholipid classes, a profile broader than sterol-only binding.

"SCP2D1 likely participates in **cellular lipid mobilization** involving lysophospholipids and glycerophospholipids and may also bind free fatty acids, suggesting a role broader than “sterol-only” binding"

A 2009 targeted siRNA screen in HeLa cells (Bartz et al.) knocked down C20orf79/SCP2D1 and observed increased filipin cholesterol staining and increased DiI-LDL uptake, implicating SCP2D1 in cholesterol homeostasis and/or LDL trafficking. Effect sizes and mechanism were not resolved, so this is hypothesis-generating rather than mechanistic.

"Reduced SCP2D1 expression produced a phenotype consistent with altered cholesterol homeostasis and/or LDL trafficking, implying SCP2D1 participates in pathways that constrain cholesterol accumulation and/or regulate LDL uptake under these conditions"

No retrieved source demonstrates SCP2D1 enzymatic catalysis or membrane-transporter activity; the available evidence supports lipid binding and lipid/cholesterol handling phenotypes only.

"No retrieved source demonstrated SCP2D1 catalyzing a biochemical reaction (enzyme activity) or acting as a membrane transporter with defined substrate translocation kinetics. The strongest current evidence supports **lipid binding** and **lipid/cholesterol handling phenotypes** rather than enzymatic catalysis"

SCP2D1 subcellular localization is underdetermined by direct evidence; no SCP2D1-specific localization experiments were found, and peroxisomal targeting features of the paralog SCP2/SCPX cannot be transferred to SCP2D1.

"No retrieved SCP2D1-specific experiments provided definitive localization (e.g., immunofluorescence of endogenous SCP2D1, organelle fractionation, proximity labeling, or tagged SCP2D1 localization). Therefore, SCP2D1 localization remains **underdetermined** from this evidence set."

SCP2D1 behaves as a cancer-testis gene: its mRNA was detected in colon cancer but not matched normal colon, it was among the most frequently expressed CT genes (~35% of patients), and it is inducible by epigenetic drugs (DNMT and HDAC inhibitors) in colon cancer cell lines. This is a non-core, expression-pattern observation rather than a molecular function.

"SCP2D1 mRNA was detected in CC but not in NC, and it was one of the most frequently expressed CT genes in that cohort"