Procyclin gene expression and loss of the variant surface glycoprotein during differentiation of Trypanosoma brucei.
In the mammalian host, the unicellular flagellate Trypanosoma brucei is covered by a dense surface coat that consists of a single species of macromolecule, the membrane form of the variant surface glycoprotein (mfVSG). After uptake by the insect vector, the tsetse fly, bloodstream-form trypanosomes differentiate to procyclic forms in the fly midgut. Differentiation is characterized by the loss of the mfVSG coat and the acquisition of a new surface glycoprotein, procyclin. In this study, the change in surface glycoprotein composition during differentiation was investigated in vitro. After triggering differentiation, a rapid increase in procyclin-specific mRNA was observed. In contrast, there was a lag of several hours before procyclin could be detected. Procyclin was incorporated and uniformly distributed in the surface coat. The VSG coat was subsequently shed. For a single cell, it took 12-16 h to express a maximum level of procyclin at the surface while the loss of the VSG coat required approximately 4 h. The data are discussed in terms of the possible molecular arrangement of mfVSG and procyclin at the cell surface. Molecular modeling data suggest that a (Asp-Pro)2 (Glu-Pro)22-29 repeat in procyclin assumes a cylindrical shape 14-18 nm in length and 0.9 nm in diameter. This extended shape would enable procyclin to interdigitate between the mfVSG molecules during differentiation, exposing epitopes beyond the 12-15-nm-thick VSG coat.
Roditi
I
I
Max-Planck-Institut für Biologie, Tübingen, Federal Republic of Germany.
Schwarz
H
H
Pearson
T W
TW
Beecroft
R P
RP
Liu
M K
MK
Richardson
J P
JP
Bühring
H J
HJ
Pleiss
J
J
Bülow
R
R
Williams
R O
RO
D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D015342:DNA Probes; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D007700:Kinetics; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009693:Nucleic Acid Hybridization; D011487:Protein Conformation; D012333:RNA, Messenger / Q000096:biosynthesis; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000378:metabolism*
D015342:DNA Probes; D012333:RNA, Messenger; D014643:Variant Surface Glycoproteins, Trypanosoma