A novel structure of GPI anchored proteins

GPI anchors many proteins to the cell surface. GPI precursor has three mannoses, all of which are modified by ethanolamine-phosphate (EthN-P). It has been believed that EthN-P on the third mannose is always used as a bridge to the protein and EthN-P on the second mannose is removed after GPI is attached to the protein. In fact, several GPI-anchored proteins are not appreciably reduced on cells defective in PIGG, which transfers EthN-P to the second mannose. Nevertheless, mutations in PIGG cause neuronal abnormalities. Here, we show that EthN-P on the second mannose is used as a preferential bridge for several GPI-anchored proteins. Our data modifies the current view of GPI anchors and provides mechanistic basis of PIGG deficiencies.