Molecular comparison of apocrine released and cytoplasmic resident carbonic anhydrase II.
We have previously shown that carbonic anhydrase II usually described as a cytoplasmic resident isoform (cCAH II) is secreted by the rat coagulating gland (sCAH II) via the apocrine secretion mode. To get more detailed information why CAH II is cytoplasmic resident in some organs and secreted in others we cloned and sequenced the cDNA of rat coagulating gland sCAH II. The sequence of the secretory form was found to be completely identical with the cCAH II. Therefore, a signal peptide targeting sCAH II for apocrine secretion can be excluded. Considering the fact that other apocrine secreted proteins are glycosylated, cCAH II and sCAH II were analyzed for carbohydrate substitutions. As expected for a cytoplasmic protein, no glycan modification could be identified in cCAH II. In contrast, sCAH II carried exclusively Gal, GlcNAc and Fuc residues in a molar ratio of 1:0.8:0.5. Carbohydrate linkage analyses demonstrated the presence of terminal Fuc, terminal, 3-substituted and 3,6-disubstituted Gal as well as 4-substituted and 3,4-disubstituted GlcNAc. The composition of the glycan constituents as well as deglycosylation experiments clearly proved that sCAH II carries neither conventional mammalian-type N-glycans nor mucin-type O-linked sugar chains. Lacking a signal peptide for ER translocation, glycosylation of sCAH II must occur within the cytoplasmic compartment. Further studies have to elucidate whether or not glycosylation of sCAH II is essential for the apocrine release of the protein.
Wilhelm
Beate
B
Institut für Anatomie und Zellbiologie, Philipps-Universität, Robert-Koch-Str. 6, 35037 Marburg, Germany. wilhelmb@mailer.uni-marburg.de
Geyer
Hildegard
H
Geyer
Rudolf
R
Schwaeble
Wilhelm
W
Linder
Monica
M
Linder
Dietmar
D
Aumüller
Gerhard
G
Seitz
Jürgen
J
D000595:Amino Acid Sequence; D000818:Animals; D001050:Apocrine Glands / Q000378:metabolism*; D001483:Base Sequence; D024402:Carbonic Anhydrase II / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000201:enzymology*; D018076:DNA, Complementary; D006031:Glycosylation; D008297:Male; D008969:Molecular Sequence Data; D051381:Rats; D017208:Rats, Wistar; D012689:Sequence Homology, Nucleic Acid
D018076:DNA, Complementary; D024402:Carbonic Anhydrase II