Ectopic epididymal expression of guinea pig intestinal phospholipase B. Possible role in sperm maturation and activation by limited proteolytic digestion.
Guinea pig intestinal phospholipase B is a calcium-independent phospholipase hydrolyzing sequentially the acyl ester bonds at sn-2 and sn-1 positions of glycerophospholipids, promoting the formation of sn-glycero-3-phosphocholine from phosphatidylcholine. This 140-kDa glycoprotein from the brush border membrane of differentiated enterocytes contributes to lipid digestion as an ectoenzyme. The cDNA coding for guinea pig phospholipase B was revealed to be the homologue of AdRab-B, an mRNA appearing in rabbit upon intestine development. The sequence predicts a polypeptide of 1463 amino acids displaying four homologous repeats, two of them containing the lipase consensus sequence GXSXG. A 5-kilobase transcript was particularly abundant in mature ileal and jejunal enterocytes but was also detected in epididymis, where phospholipase B displayed a higher molecular mass (170 kDa versus 140 kDa in intestine), with no obvious evidence for enzyme activity. Trypsin treatment of phospholipase B immunoprecipitated from epididymal membranes reduced its size to 140 kDa, coinciding with the appearance of a significant phospholipase A2 activity. The same results were obtained in COS cells transfected with phospholipase B cDNA. Since sn-glycero-3-phosphocholine present at high concentrations in seminal plasma mainly stems from epididymis, this suggests a possible role of phospholipase B in male reproduction. This novel localization also unravels a mechanism of phospholipase B activation by limited proteolysis involving either trypsin in the intestinal lumen or a trypsin-like endopeptidase in the male reproductive tract.
Delagebeaudeuf
C
C
Institut Fédératif de Recherche en Immunologie Cellulaire et Moléculaire, Université Paul Sabatier, Toulouse Cedex, France.
Gassama-Diagne
A
A
Nauze
M
M
Ragab
A
A
Li
R Y
RY
Capdevielle
J
J
Ferrara
P
P
Fauvel
J
J
Chap
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D018076:DNA, Complementary; D004822:Epididymis / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic; D006168:Guinea Pigs; D006868:Hydrolysis; D007082:Ileum / Q000166:cytology / Q000201:enzymology*; D007583:Jejunum / Q000166:cytology / Q000201:enzymology*; D008245:Lysophospholipase / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D011817:Rabbits; D017386:Sequence Homology, Amino Acid
D018076:DNA, Complementary; D008245:Lysophospholipase