Abstract
There are several antigenic variants in Rickettsia tsutsugamushi, and a type-specific antigen (TSA) of 56-kilodaltons located on the rickettsial surface is responsible for the variation. The primary structures of the protein in two variants, Gilliam and Karp, have been reported independently by us and Stover et al. by cloning and sequencing the corresponding genes (Ohashi, N., Nashimoto, H., Ikeda, H., and Tamura, A. (1990) Gene (Amst.) 91, 119-122; Stover, C. K., Marana, D. P., Carter, J. M., Roe, B. A., Mardis, E., and Oaks, E. V. (1990) Infect. Immun. 58, 2076-2084). In the present study, genes encoding the TSA homologues of the other four variants, Kato, Kawasaki, Kuroki, and Shimokoshi, which are all distinguishable serologically, were cloned and sequenced, and consequently, it became possible to compare the primary structures of the six antigenic variants. The sequence analyses revealed a complete open reading frame encoding 55,308-56,745-dalton proteins with 521-532 amino acids, in which a putative signal peptide consisting of 22 amino acids was recognized at the NH2-terminal end. Transcription of the gene is regulated by several tandem promoters. All TSA molecules have the characteristics of transmembrane proteins with alternating hydrophobic and hydrophilic regions, and contain four variable domains with spans of 16-40 amino acids which are located in the hydrophilic regions in the molecule and show different amino acid sequences among the strains. Phylogenetic classification among the R. tsutsugamushi strains based on TSA homologues supports the antigenic relationships known in the closely and distantly related strains.
Highlights
There are several antigenic variants in Rickettsia tsutsugamushi, and a type-specific antigen (TSA) of 56-kilodaltons located on the rickettsial surfaceis responsible for the variation.The primary structuresof the protein in two variants, Gilliam and Karp, have been reported independently by us and Stoveret al.by cloning and sequencing the corresponding genes (Ohashi,N., Nashimoto, H., Ikeda, H., and Tamura,A. (1990) Gene (Amst.)91,119-122; Stover, C
Hydrophobicand hydrophilic regions, and contain four Our recent comparative analysis of the NHn-terminal amino variable domains with spans of 16-40 amino acids acid sequences of three TSA homologues purified from the which are located in the hydrophilic regions in the molecule and show different amino acid sequences among the strains
Comparison of hydropathic profiles in each domain among the strains shows: (i) the profiles in the VDI region can be divided into two types, such as the Gilliam, Kuroki, Karp, and Kawasaki types, and the Kat0 and Shimokoshi types; (ii) the patterns in the VDII region are almost unique in each TSA protein; (iii) the profiles in the VDIII region are similar to each other except that of the Shimokoshi strain; (iv) theVDIV region locates in the largest hydrophilic area in the molecule and the patterns are more
Summary
Gene Structures of Rickettsial TSA Homologues-We sequenced 2,272 bp (Kato), 2,260 bp (Kawasaki), 2,284 bp (Kuroki) and 2,303 bp (Shimokoshi) in the cloned rickettsial. L cells with two kinds of primers to determine the initial site tsg (Gilliam) and sta (Karp) genes correspond to P2 and of transcription (Fig. 2), three major (PI-P3)and some minor P4 regions, respectively. The putative sequences of the -35 and -10 promoter codon, which was identified as a potential ribosome-binding regions seen a t 7-37 bp upstream from the 5'-end of four site in the previous study ( l l ) , is recognized in the genes from transcripts were TATACT and TATAAA (PI),TTTACA all strains (Fig. 3 and 4). From comparison of the amino acid sequences in the NH2-terminal region of TSAs, the sequences of 22 amino acid residues on the NH2-terminal side which are encoded by the tsw (Kawasaki), tsr (Kuroki), and tss (Shimokoshi) genes are predicted as signal peptides (Fig. 4, B-D). KurOkl Shmkoshl Gilllam x.rp z- IF351 GCAGATTAGA c"-- Prim- er- 1 --
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