These phosphotransfer enzymes catalyze both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) biosynthesis from CDP-choline and CDP-ethanolamine, respectively, plus diglycerides, in a process coupled to transmembrane phospholipid transport to distribute phosphatidyl choline to the lumenal surface of the endoplasmic reticulum (Henneberry et al. 2000).

The human CEPT1 uses diradylglycerols (diacylglycerols) as substrates, and the fatty acyl specificities of CEPT1 for these molecules in a mixed micellar assay have been studied (Wright and McMaster 2002). CEPT1 displayed an apparent Km of 36 microM for CDP-choline and 4.2 mol% for di-18:1 DAG with a Vmax of 14.3 nmol/min/mg. When CDP-ethanolamine was used as substrate, the apparent Km was 98 microM for CDP-ethanolamine and 4.3 mol% for di-18:1 DAG with a Vmax of 8.2 nmol/min/mg. The preferred diradylglycerol substrates used by CEPT1 with CDP-choline as the phosphobase donor were di-18:1 DAG, di-16:1 DAG, and 16:0/18:1 DAG. When CDP-ethanolamine was used as the phosphobase donor, 16:0/18:1 DAG, di-18:1 DAG, and di-16:1 DAG were the preferred substrates. The mixed micelle assay allowed the lipid activation of CEPT to be measured, and both the cholinephosphotransferase and ethanolaminephosphotransferase activities displayed the unusual property of product activation. The protein kinase C inhibitor chelerythrine and the human DAG kinase inhibitor R59949 both inhibited CEPT1 activity with IC50 values of 40 microM (Wright and McMaster 2002).

4.F.1 The Choline/Ethanolaminephosphotransferase 1 (CEPT1) Family These phosphotransfer enzymes catalyze both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) biosynthesis from CDP-choline and CDP-ethanolamine, respectively, plus diglycerides, in a process coupled to transmembrane phospholipid transport to distribute phosphatidyl choline to the lumenal surface of the endoplasmic reticulum (Henneberry et al. 2000). The human CEPT1 uses diradylglycerols (diacylglycerols) as substrates, and the fatty acyl specificities of CEPT1 for these molecules in a mixed micellar assay have been studied (Wright and McMaster 2002). CEPT1 displayed an apparent Km of 36 microM for CDP-choline and 4.2 mol% for di-18:1 DAG with a Vmax of 14.3 nmol/min/mg. When CDP-ethanolamine was used as substrate, the apparent Km was 98 microM for CDP-ethanolamine and 4.3 mol% for di-18:1 DAG with a Vmax of 8.2 nmol/min/mg. The preferred diradylglycerol substrates used by CEPT1 with CDP-choline as the phosphobase donor were di-18:1 DAG, di-16:1 DAG, and 16:0/18:1 DAG. When CDP-ethanolamine was used as the phosphobase donor, 16:0/18:1 DAG, di-18:1 DAG, and di-16:1 DAG were the preferred substrates. The mixed micelle assay allowed the lipid activation of CEPT to be measured, and both the cholinephosphotransferase and ethanolaminephosphotransferase activities displayed the unusual property of product activation. The protein kinase C inhibitor chelerythrine and the human DAG kinase inhibitor R59949 both inhibited CEPT1 activity with IC50 values of 40 microM (Wright and McMaster 2002).
References:
Chauhan, N., L. Farine, K. Pandey, A.K. Menon, and P. Bütikofer. (2016). Lipid topogenesis - 35years on. Biochim. Biophys. Acta. [Epub: Ahead of Print]
Dewey, R.E., R.F. Wilson, W.P. Novitzky, and J.H. Goode. (1994). The AAPT1 gene of soybean complements a cholinephosphotransferase-deficient mutant of yeast. Plant Cell 6: 1495-1507.
Henneberry, A.L., G. Wistow, and C.R. McMaster. (2000). Cloning, genomic organization, and characterization of a human cholinephosphotransferase. J. Biol. Chem. 275: 29808-29815.
Parsons, W.H., M.J. Kolar, S.S. Kamat, A.B. Iii, J.J. Hulce, E. Saez, B.B. Kahn, A. Saghatelian, and B.F. Cravatt. (2016). AIG1 and ADTRP are atypical integral membrane hydrolases that degrade bioactive FAHFAs. Nat Chem Biol 12: 367-372.
Sciara, G., O.B. Clarke, D. Tomasek, B. Kloss, S. Tabuso, R. Byfield, R. Cohn, S. Banerjee, K.R. Rajashankar, V. Slavkovic, J.H. Graziano, L. Shapiro, and F. Mancia. (2014). Structural basis for catalysis in a CDP-alcohol phosphotransferase. Nat Commun 5: 4068.
Wright, M.M. and C.R. McMaster. (2002). PC and PE synthesis: mixed micellar analysis of the cholinephosphotransferase and ethanolaminephosphotransferase activities of human choline/ethanolamine phosphotransferase 1 (CEPT1). Lipids 37: 663-672.
Examples:
TC#	Name	Organismal Type	Example
4.F.1.1.1	*Choline/Ethanolamine phosphotransferase phospholipid flipping group translocator, CEPT1, of 416 aas and 8 - 10 TMSs (Henneberry et al.* 2000).**		CEPT1 of Homo sapiens

4.F.1.1.2	Amino alcohol phosphotransferase, AAPT of 389 aas and 8 TMSs. Catalyzes both phosphatidylcholine and phosphatidylethanolamine biosynthesis from CDP-choline and CDP-ethanolamine, respectively. Has a higher cholinephosphotransferase activity than ethanolaminephosphotransferase activity (Dewey et al. 1994).		*AAPT1 of Arabidopsis thaliana* (Mouse-ear cress)**

4.F.1.1.3	Putative choline/ethanolamine phosphotransferase (CEPT) of 417 aas and 8 - 10 TMSs		CEPT of Leishmania infantum

4.F.1.1.4	Uncharacterized protein of 380 aas and 8 - 11 TMSs		UP of Paramecium tetraurelia

4.F.1.1.5	CDP-alcohol phosphatidyltransferase, CAPT, of 244 aas and 8 TMSs in a 2 + 2 + 2+ 2 arrangement.		CAPT of Marinobacter excellens

4.F.1.1.6	Uncharacterized protein of 377 aas and 6 TMSs		UP of Novosphingobium tardaugens

4.F.1.1.7	CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase, PgsA of 189 aas and 6 TMSs		PgsA of Leifsonia xyli

4.F.1.1.8	CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase, PgsA, of 186 aas and 6 TMSs		PgsA of Pseudomonas fluorescens

4.F.1.1.9	Uncharacterized protein of 302 aas and 7 TMSs		UP of Planctomycetes bacterium (groundwater metagenome)

Examples:
TC#	Name	Organismal Type	Example
4.F.1.2.1	Uncharacterized protein of 230 aas and 6 TMSs		UP of Sphingobium japonicum

4.F.1.2.2	Uncharacterized protein of 268 aas and 6 TMSs		UP of Paraprevotella clara

Examples:
TC#	Name	Organismal Type	Example
4.F.1.3.1	CDP-alcohol phosphatidyltransferase, CAPT, of 189 aas and 4 TMSs		CAPT of Thermococcus kodakarensis (Pyrococcus kodakaraensis)

4.F.1.3.2	CDP-alcohol phosphatidyltransferase, CAPT, of 210 aas and 5 - 7 TMSs		CAPT of Terriglobus saanensis

4.F.1.3.3	CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase, PgsA of 201 aas and 6 TMSs		PgsA of E. coli

4.F.1.3.4	CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase, PgsA, of 202 aas and 6 probable TMSs.		PgsA of Halalkalicoccus jeotgali

4.F.1.3.5	Uncharacterized protein of 308 aas and 4 - 5 TMSs		UP of Ignavibacteria bacterium

Examples:
TC#	Name	Organismal Type	Example