Low-resolution structure of the soluble domain GPAA1 (yGPAA170–247) of the glycosylphosphatidylinositol transamidase subunit GPAA1 from Saccharomyces cerevisiae

The GPI (glycosylphosphatidylinositol) transamidase complex catalyses the attachment of GPI anchors to eukaryotic proteins in the lumen of ER (endoplasmic reticulum). The Saccharomyces cerevisiae GPI transamidase complex consists of the subunits yPIG-K (Gpi8p), yPIG-S (Gpi17p), yPIG-T (Gpi16p), yPIG-U (CDC91/GAB1) and yGPAA1. We present the production of the two recombinant proteins yGPAA170–247 and yGPAA170–339 of the luminal domain of S. cerevisiae GPAA1, covering the amino acids 70–247 and 70–339 respectively. The secondary structural content of the stable and monodisperse yGPAA170–247 has been determined to be 28% α-helix and 27% β-sheet. SAXS (small-angle X-ray scattering) data showed that yGPAA170–247 has an Rg (radius of gyration) of 2.72±0.025 nm and Dmax (maximum dimension) of 9.14 nm. These data enabled the determination of the two domain low-resolution solution structure of yGPAA170–247. The large elliptical shape of yGPAA170–247 is connected via a short stalk to the smaller hook-like domain of 0.8 nm in length and 3.5 nm in width. The topological arrangement of yGPAA170–247 will be discussed together with the recently determined low-resolution structures of yPIG-K24–337 and yPIG-S38–467 from S. cerevisiae in the GPI transamidase complex.