Communicative functions of GPI-anchored surface proteins in unicellular eukaryotes

Abstract

Research on several unicellular eukaryotes has identified communicative surface proteins, which are anchored to the outer membrane by glycosylphosphatidylinositol (GPI). Surprisingly, these surface proteins are also released into the environment, raising questions regarding the underlying adaptive advantages and the physical mechanisms that allow for this shedding. This article reviews the current knowledge on several GPI-proteins of different protist species, assembles the puzzling data on the different functions of surface bound and released forms of these proteins, and summarizes their contribution to intra- and interspecific signaling. Recent advances in biochemistry and glycobiology indicate that the GPI-anchor is one of the prerequisites of protein function of membrane bound as well as of released proteins, and hence is a crucial invention for microbial molecular communication. The sensitivity of GPI-anchors (e.g. to phospholipase C) requires consideration of environmental lipase activity of different sources in microbial communities, as these may represent exogenous factors involved in surface protein release. We hypothesize a complex surface protein based communication network and discuss the known facts on protist GPIs in an evolutionary context.

Keywords::

• Cell–cell communication
• antigenic variation
• kairomone
• phospholipase C
• glycosylphosphatidylinositol

Acknowledgment

We thank Tina Klöppel for preparation of Figures 1 and 2, Ilse Winkler-Reske for drawings of protists and Mandy Huckins for helpful comments on the manuscript.

Declaration of interest

This work was supported by grant SI1397/2-1 to M.S. by the German Science Foundation (DFG). The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.