关键词: 蓝氏贾第鞭毛虫, 表面变异抗原, 序列分析, 同源性, 克隆

Abstract: Objective To clone and sequence variant-specific surface antigen gene from Giardia lamblia isolate SUCH/89/BTMRI/2（C2） derived from human in China. Methods Total genomic DNA of G. lamblia was extracted and a full-length variant-specific surface antigen gene fragment was amplified by polymerase chain reaction （PCR）. The PCR product was cloned into pMD19-T simple-vector， transformed into an Escherichia coli JM109 strain and then sequenced.The sequence analysis for cloned fragment was finished by Vector NTI 9.0 software for the homology of Giardia variant-specific surface antigen gene to that of sequences publishend in GenBank. Results The full-length variant-specific surface antigen gene fragment from G. lamblia was found to be 2 142 bp， encoding a 713 amino acid polypeptide and contained a single open reading frame （ORF）. The deduced polypeptide sequence was rich in cysteine （11.8 mol%）， most of which occurred with in 29 copies of the 4-amino acid CXXC motif， one GGCY-tetrapeptide motifs and three NXS consensus N-linked glycosylation sites. This polypeptide was also rich in threonine （10.2 mol%）， glycine （12.1 mol%） and alanine （10.1 mol%）. Like other previously identified VSPs， it contained a highly conserved hydrophobic C-terminal region. The homology of G. lamblia SUCH/89/BTMRI/2(C2) variant-specific surface antigen gene to that of sequence（TSA417） published in GenBank was 99% both at the nueleotide and the amino acid levels. Conclusion The full length variant-specific surface antigen gene from the isolate of G. lamblia has the common characteristics with other previously identified VSPs.

Key words: Giardia lamblia, Variant-specific surface antigen, Sequence, Homology, Clone