title: Determinants of the membrane orientation of a calcium signaling enzyme CD38.
abstract: CD38 catalyzes the synthesis of two structurally distinct messengers for Ca²⁺-mobilization, cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP), from cytosolic substrates, NAD and NADP, respectively. CD38 is generally thought of as a type II membrane protein with its catalytic site facing outside. We recently showed that CD38 exists, instead, in two opposite membrane orientations. The determinant for the membrane topology is unknown. Here, specific antibodies against type III CD38 were designed and produced. We show that mutating the positively charged residues in the N-terminal tail of CD38 converted its orientation to type III, with the catalytic domain facing the cytosol and it was fully active in producing intracellular cADPR. Changing the serine residues to aspartate, which is functionally equivalent to phosphorylation, had a similar effect. The mutated CD38 was expressed intracellularly and was un-glycosylated. The membrane topology could also be modulated by changing the highly conserved di-cysteine. The results indicate that the net charge of the N-terminal segment is important in determining the membrane topology of CD38 and that the type III orientation can be a functional form of CD38 for Ca²⁺-signaling. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
authors.affiliation: School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, 2199 Lishui Road, Nanshan District, Shenzhen, China; Department of Physiology, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong. Electronic address: zhaoyongjuan@gmail.com.
authors.forename: Yong Juan
authors.initials: YJ
authors.lastname: Zhao
authors.affiliation: School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, 2199 Lishui Road, Nanshan District, Shenzhen, China.
authors.forename: Wen Jie
authors.initials: WJ
authors.lastname: Zhu
authors.affiliation: Functional Laboratory, School of Medicine, Yangtze University, 1 Nanhuan Road, Jingzhou, Hubei China.
authors.forename: Xian Wang
authors.initials: XW
authors.lastname: Wang
authors.affiliation: School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, 2199 Lishui Road, Nanshan District, Shenzhen, China; State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, 38 Xueyuan Road, Haidian District, Beijing, China.
authors.forename: Li-He
authors.initials: LH
authors.lastname: Zhang
authors.affiliation: School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, 2199 Lishui Road, Nanshan District, Shenzhen, China. Electronic address: leehoncheung@gmail.com.
authors.forename: Hon Cheung
authors.initials: HC
authors.lastname: Lee
mesh_terms: D051997:ADP-ribosyl Cyclase 1 / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002462:Cell Membrane / Q000201:enzymology* / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009249:NADP / Q000031:analogs & derivatives* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D017434:Protein Structure, Tertiary
chemical_list: D008562:Membrane Glycoproteins; D009249:NADP; C024376:NAADP; C498154:CD38 protein, human; D051997:ADP-ribosyl Cyclase 1
keywords: ADP-ribosyl cyclase; CD38; Calcium signaling; Cyclic ADP-ribose; Membrane topology