Chromogranin A-like proteins in the secretory granules of a protozoan, Paramecium tetraurelia.
The ciliate protozoan Paramecium tetraurelia produces secretory granules (trichocysts) which release needle-like structures composed of small, acidic proteins. Using antibodies against isolated chromogranin A (CGA) and against trichocyst proteins, we found cross-reactive proteins in chromaffin granules and trichocysts. Four independently derived sera against isolated CGA stained bands of the Mr 15,000-25,000 family of trichocyst proteins on immunoblots. A positive response was also obtained with antiserum against chemically synthesized peptides (PL26 and GE25) corresponding to defined regions of the CGA amino acid sequence. In extracts of whole Paramecium, larger proteins (Mr 53,000 and 49,000) also reacted with antibodies against CGA and the related synthetic peptides. These larger proteins may represent unprocessed precursors to the smaller proteins of mature trichocysts. Antiserum to trichocysts recognized CGA in chromaffin granule lysates. Further evidence of a Paramecium protein related to CGA was provided by hybridization of Paramecium mRNA with cloned cDNA for bovine CGA. Our results suggest striking conservation in evolution of CGA-like proteins that may play some role, as yet unknown, in secretion.
Department of Biochemistry, University of Wisconsin-Madison 53706-1569.
J B
JB
Peterson
D L
DL
Nelson
E
E
Ling
R H
RH
Angeletti
D000818:Animals; D002417:Cattle; D053379:Chromogranin A; D002864:Chromogranins / Q000032:analysis*; D003429:Cross Reactions; D003594:Cytoplasmic Granules / Q000032:analysis*; D004247:DNA / Q000378:metabolism; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000032:analysis*; D009693:Nucleic Acid Hybridization; D010247:Paramecium / Q000648:ultrastructure*; D012333:RNA, Messenger / Q000378:metabolism
D053379:Chromogranin A; D002864:Chromogranins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D004247:DNA