Trypanosoma evansi: identification and characterization of a variant surface glycoprotein lacking cysteine residues in its C-terminal domain.
African trypanosomes are flagellated unicellular parasites which proliferate extracellularly in the mammalian host blood-stream and tissue spaces. They evade the hosts' antibody-mediated lyses by sequentially changing their variant surface glycoprotein (VSG). VSG tightly coats the entire parasite body, serving as a physical barrier. In Trypanosoma brucei and the closely related species Trypanosoma evansi, Trypanosoma equiperdum, each VSG polypeptide can be divided into N- and C-terminal domains, based on cysteine distribution and sequence homology. N-terminal domain, the basis of antigenic variation, is hypervariable and contains all the exposed epitopes; C-terminal domain is relatively conserved and a full set of four or eight cysteines were generally observed. We cloned two genes from two distinct variants of T. evansi, utilizing RT-PCR with VSG-specific primers. One contained a VSG type A N-terminal domain followed a C-terminal domain lacking cysteine residues. To confirm that this gene is expressed as a functional VSG, the expression and localization of the corresponding gene product were characterized using Western blotting and immunofluorescent staining of living trypanosomes. Expression analysis showed that this protein was highly expressed, variant-specific, and had a ubiquitous cellular surface localization. All these results indicated that it was expressed as a functional VSG. Our finding showed that cysteine residues in VSG C-terminal domain were not essential; the conserved C-terminal domain generally in T. brucei like VSGs would possibly evolve for regulating the VSG expression.
Jia
Yonggen
Y
Parasitology Laboratory, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
Zhao
Xinxin
X
Zou
Jingru
J
Suo
Xun
X
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002020:Buffaloes; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005786:Gene Expression Regulation; D007106:Immune Sera / Q000096:biosynthesis; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D014345:Trypanosoma / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D014352:Trypanosomiasis / Q000469:parasitology; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000737:chemistry* / Q000235:genetics
D007106:Immune Sera; D014643:Variant Surface Glycoproteins, Trypanosoma; D003545:Cysteine