Table I. Type II membrane proteins that are significantly altered ectopic expression of catalytically active SPPL3 in HEK293 cells. The table contains all membrane proteins with type II orientation which are significantly (p value ≤ 0.05) increased or decreased upon SPPL3 overexpression. Those type II proteins that were more abundantly secreted following SPPL3 overexpression are shown above the dotted line, those secreted less below. Indicated are the names of the proteins, the gene name, number of unique peptides, the mean of the ratio between SPPL3 overexpression and control (con) of 5 biological replicates and the p value calculated with a two-sided, heteroscedastic t-test based on the log2 transformed LFQ values for the control and the SPPL3 overexpression condition. Previously published SPPL3 substrates are highlighted in bold, those identified also in the MEF screen (Fig. 3 and Table II) in italics.

Protein names	Gene name	Unique peptides	Mean ratio SPPL3/Con	p value
Aspartyl/asparaginyl beta-hydroxylase	ASPH	35	287.58	1.53E-04
Gamma-glutamyltransferase 7	GGT7	13	122.60	1.00E-06
Torsin-1A-interacting protein 2	TOR1AIP2	2	77.17	7.11E-05
Cytoskeleton-associated protein 4	CKAP4	17	21.11	6.05E-03
Exostosin-like 3	EXTL3	13	17.98	1.51E-02
Adipocyte plasma membrane-associated protein	APMAP	6	17.93	8.08E-04
Glutaminyl-peptide cyclotransferase-like protein	QPCTL	3	11.88	2.49E-03
Sodium/potassium-transporting ATPase subunit beta-1	ATP1B1	4	10.37	4.79E-05
Probable inactive protein kinase-like protein SgK196	SGK196	12	7.35	3.32E-05
Endoplasmic reticulum mannosyl-oligosaccharide 1,2-alpha-mannosidase	MAN1B1	14	6.99	9.64E-05
2-oxoglutarate and iron-dependent oxygenase domain-containing protein 3	OGFOD3	7	6.63	4.13E-03
Beta-1,4-galactosyltransferase 7	B4GALT7	3	5.96	8.16E-05
Heparan-sulfate 6-O-sulfotransferase 2	HS6ST2	15	5.05	1.28E-04
Beta-1,3-galactosyltransferase 6	B3GALT6	9	3.92	5.54E-04
Xylosyltransferase 2	XYLT2	15	3.27	9.39E-03
Alpha-mannosidase 2x	MAN2A2	33	3.18	3.42E-03
Type 2 lactosamine alpha-2,3-sialyltransferase	ST3GAL6	5	3.08	1.11E-02
Bifunctional heparan sulfate N-deacetylase/N-sulfotransferase 1	NDST1	21	3.05	1.48E-06
Protein ITFG3	ITFG3	4	2.78	3.34E-02
Endothelin-converting enzyme 1	ECE1	15	2.76	6.11E-04
Ectonucleoside triphosphate diphosphohydrolase 6	ENTPD6	10	2.71	1.49E-03
Fukutin-related protein	FKRP	2	2.46	2.59E-02
Alpha-1,3-mannosyl-glycoprotein 2-beta-N-acetylglucosaminyltransferase	MGAT1	15	2.38	4.44E-02
Heparan-sulfate 6-O-sulfotransferase 1	HS6ST1	10	2.13	3.14E-02
Bifunctional heparan sulfate N-deacetylase/N-sulfotransferase 2	NDST2	14	1.90	3.52E-02
Heparan sulfate glucosamine 3-O-sulfotransferase 3B1	HS3ST3B1	9	0.58	4.27E-02
Cyclic AMP-dependent transcription factor ATF-6 alpha	ATF6	3	0.36	3.06E-02
N-acetyllactosaminide beta-1,3-N-acetylglucosaminyltransferase	B3GNT1	19	0.30	1.95E-02