GLYCOPHOSPHATIDYLINOSITOL-ANCHORED PROTEINS INPARAMECIUM TETRAURELIA

Abstract

SUMMARYWe have begun to characterize the glycophosphatidylinositol (GPI)-anchored proteins of the Paramecium tetraurelia cell body surface where receptors and binding sites for attractant stimuli are found. We demonstrate here (i) that inositol-specific exogenous phospholipase C (PLC) treatment of the cell body membranes (pellicles) removes proteins with GPI anchors, (ii)that, as in P. primaurelia, there is an endogenous lipase that responds differently to PLC inhibitors compared with its response to an exogenous PLC, (iii) that salt and ethanol treatment of cells removes GPI-anchored proteins from whole, intact cells, (iv) that Triton X-114 phase partitioning shows that many GPI-anchored proteins are cleaved from pellicles by the endogenous lipase and enter the aqueous phase, and (v) that integral membrane proteins are not among those cleaved with PLC or in the salt/ethanol wash.Antisera against the proteins removed by the salt/ethanol washing procedure include antibodies against large surface antigens, which we confirm in this species to be GPI-anchored, and against an array of proteins of smaller molecular mass. These antisera specifically block the chemoresponse to some stimuli, such as folate, which we suggest are signaled through GPI-anchored receptors. Responses to cyclic AMP, which we believe involve an integral membrane protein receptor, and to NH4Cl, which requires no receptor, are not affected by the antisera. Antiserum against a mammalian GPI-anchored folate-binding protein recognizes a single band among the GPI-anchored salt and ethanol wash proteins. The same antiserum specifically blocks the chemoresponse to folate.

Species-Specific Duplication of Surface Antigen Genes in Paramecium

“…For instance, the addition of homologous antibodies to living paramecia induces serotype switches [22] and this was also reported recently for several other organisms, e.g., Giardia, Trypanosoma, and the ciliate Tetrahymena [23]. Furthermore, the GPI-anchored folate receptor on the Paramecium surface was shown to confer a folate-specific chemoresponse [24]; thus, GPI-mediated signal transduction appears to exist in Paramecium.…”

“…Proteins with transmembrane domains were almost exclusively found in group 7. Classical SAgs, as well as many smaller cysteine-rich surface antigens, have been shown to be GPI-anchored [12,15,20,24] and this fit to all other groups. Transmembrane domaincontaining proteins with cysteine repeat structures have been reported in P. tetraurelia before, but through just a genomic screen, nothing is known about their expression, localization, and function [26].…”

A Review for the Special Issue on Paramecium as a Modern Model Organism

“…In cells entering into conjugation and sexual reproduction, the Mic initiates DNA replication and meiosis late in the cell cycle while the cells are in G2 [30]. Fujishima describes the preparation of Mics for entry into meiosis [67]. At 2-2.5 h after mixing, during the Mic pre-meiotic S phase, the mating reactive cells commit to the degradation of the Mac.…”