CD39-L4 is a secreted human apyrase, specific for the hydrolysis of nucleoside diphosphates.
The human ecto-apyrase gene family consists of five reported members (CD39, CD39-L1, CD39-L2, CD39-L3, and CD39-L4). The family can be subdivided into two groups by conservation of proposed structural domains. The CD39, CD39-L1, and CD39-L3 genes all encode hydrophobic portions in their carboxy and amino termini, serving as transmembrane domains for CD39 and potentially for the other two members. CD39-L2 and CD39-L4 genes encode hydrophobic portions in their amino termini, suggesting that they might encode secreted apyrases. We demonstrate that the CD39-L4 gene encodes the first reported human secreted ecto-apyrase. COS-7 cells transfected with a CD39-L4 expression construct utilizing the naturally occurring leader peptide express recombinant protein outside of the cells. This expression can be blocked by brefeldin A, a chemical that inhibits a step in mammalian secretory pathways. We also demonstrate expression of CD39-L4 message in macrophages, suggesting that the protein is present in the circulation. Furthermore, we show that CD39-L4 is an E-type apyrase, is dependent on calcium and magnesium cations, and has high degree of specificity for NDPs over NTPs as enzymatic substrates. A potential physiological role in hemostasis and platelet aggregation is presented.
Functional Genomics Department, Hyseq Inc., Sunnyvale, California 94086, USA.
J J
JJ
Mulero
G
G
Yeung
S T
ST
Nelken
J E
JE
Ford
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000251:Adenosine Triphosphatases; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D001081:Apyrase / Q000378:metabolism*; D001483:Base Sequence; D019556:COS Cells; D002413:Cations, Divalent; D017931:DNA Primers; D004789:Enzyme Activation; D006801:Humans; D006868:Hydrolysis; D013379:Substrate Specificity
D015703:Antigens, CD; D002413:Cations, Divalent; D017931:DNA Primers; D000244:Adenosine Diphosphate; D000251:Adenosine Triphosphatases; D001081:Apyrase; C067869:CD39 antigen