Am. J. Respir. Cell Mol. Biol.,
Volume 25, Number 4, October, 2001 466-473
Functional Glycosylphosphatidylinositol Anchor Signal Sequences in the
Pneumocystis carinii PRT1 Protease Family
Robert J.
Palmer
and
Ann E.
Wakefield
Molecular Infectious Diseases Group, Department of Pediatrics, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford,
United Kingdom
Pneumocystis carinii is fungus which is a frequent cause of severe pneumonia in immunocompromised individuals. The
P. carinii genome contains the PRT1 subtelomeric multigene
family that encodes a kexin-like serine protease which is expressed on the surface of P. carinii. Analysis of the sequence of
the carboxy-terminal sequence of many copies of PRT1 showed
that they contained motifs characteristic of a glycosylphosphatidylinositol (GPI) anchor signal sequence. The ability of
the C-terminal sequences of PRT1 to direct the addition of a
GPI anchor was tested. CD14, a GPI-anchored monocyte glycoprotein antigen, was used as the basis of a heterologous system. CD14 was truncated to remove the carboxy-terminal
sequences responsible for GPI-anchor addition. Addition of
carboxy-terminal sequences from PRT1 restored high-level
surface expression to the truncated CD14. Further, the majority of CD14-PRT1 recombinant protein was removed from the
cell membrane by treatment with GPI-specific phospholipase
C. These results suggest that the carboxy-terminal residues of
most of the members of the PRT1 family of proteases have the
potential to form a functional GPI-attachment signal.
Abbreviations: complementary DNA, cDNA; fetal bovine serum, FBS;
fluorescein isothiocyanate, FITC; glycosylphosphatidylinositol, GPI;
kexin, KEX; monoclonal antibody, mAb; relative molecular mass, Mr; major surface glycoprotein, MSG; phosphate-buffered saline, PBS; polymerase chain reaction, PCR; plaque-forming units, pfu; phosphatidylinositol-specific phospholipase C, PIPLC; sodium dodecyl sulfate polyacrylamide
gel electrophoresis, SDS-PAGE.
