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J Med Microbiol 56 (2007), 715-721; DOI: 10.1099/jmm.0.46943-0
© 2007 Society for General Microbiology
ISSN 1473-5644

Molecular characterization and analysis of a gene encoding the acidic repeat protein (Arp) of Treponema pallidum

Hsi Liu1, Berta Rodes1,2, Robert George1 and Bret Steiner1

1 National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA

2 Hospital Carlos III, Madrid, Spain

Correspondence
Hsi Liu
hcl6{at}cdc.gov

Received 13 September 2006
Accepted 5 February 2007

The acidic repeat protein (arp) genes from three subspecies of the treponeme Treponema pallidum (T. pallidum subsp. pallidum, Nichols strain; T. pallidum subsp. pertenue, CDC-1 and CDC-2 strains; and T. pallidum subsp. endemicum, Bosnia A strain) were cloned and sequenced. The predicted protein sequence contained a high percentage of glutamic acid, hence the name acidic repeat protein, or Arp. The protein had a potential membrane-spanning domain and a signal peptidase I site. The gene from the Nichols strain of T. pallidum subsp. pallidum contained a set of 14 nearly identical repeats of a 60 bp sequence, which occupied ~51 % of the length of the gene. Analyses of arp from laboratory strains showed that the 5' and 3' ends of the genes were conserved, but there was considerable heterogeneity in the number of repeats of this 60 bp sequence. Based on amino acid variations, the 14 sequence repeats could be classified into three types, which were named type I, type II and type III repeats. The type II repeat was the most common in the strains examined. The arp gene of the Nichols strain was subsequently cloned into the expression vector pBAD/TOPO ThioFusion. The expressed protein was detected in a Western blot assay using rabbit immune sera produced against T. pallidum, or synthetic peptides derived from the repeat sequences. Using an ELISA, rapid plasma reagin (RPR) test-positive sera reacted with synthetic peptides derived from the repeat region but not with peptides derived from N and C termini of the Arp protein. These results show that the Arp protein is immunogenic and could prove to be a useful target for serological diagnosis of T. pallidum infection.

Abbreviations: CDC, Centers for Disease Control and Prevention; HRP, horseradish peroxidase; Ni-NTA, nickel-nitriloacetate; p.i., post-infection; RPR, rapid plasma reagin.

The GenBank/EMBL/DDBJ accession numbers for the T. pallidum subsp. pallidum, Nichols, T. pallidum subsp. endemicum, Bosnia A, T. pallidum subsp. pertenue, CDC-1, and T. pallidum subsp. pertenue, CDC-2 strains are AF411124, AF342807, AF411126 and AF342806, respectively.






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