A protective protein antigen of Rickettsia rickettsii has tandemly repeated, near-identical sequences.
The nucleotide sequence of a Rickettsia rickettsii gene that encodes a high-molecular-mass surface antigen (190 kilodaltons), which elicits protective immunity, was determined. The 6,747-nucleotide gene coded for a 2,249-amino-acid protein with a calculated molecular weight of 224,321. A 3.8-kilobase PstI fragment proximal to the 5' end of the gene was found to consist of 13 highly related tandem repeats which constituted over 40% of the coding region. The repeated sequences could be divided into either a 225-nucleotide, 75-amino-acid unit (type I) or a 216-nucleotide, 72-amino-acid unit (type II), with extensive homology between the two types of repeating units. The deduced amino acid sequence for these repeat units, overall, was slightly hydrophobic with short hydrophilic domains. The carboxy-terminal (nonrepetitive) portion of the deduced protein sequence was hydrophilic, with potential surface-exposed epitopes. The full-length reading frame was reconstructed in Escherichia coli, and transient expression of the 190-kilodalton antigen was demonstrated; however, the protein appeared to be severely degraded by proteases and was apparently toxic to E. coli. The conservation of this unique repetitive gene structure, coupled with results from previous reports showing the protective properties of the 190-kilodalton antigen, suggests that this protein plays an important role in the pathogenesis of and immunity to Rocky Mountain spotted fever.
Anderson
B E
BE
Division of Viral and Rickettsial Diseases, Centers for Disease Control, Atlanta, Georgia 30333.
McDonald
G A
GA
Jones
D C
DC
Regnery
R L
RL
D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000235:genetics* / Q000276:immunology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012091:Repetitive Sequences, Nucleic Acid; D012284:Rickettsia rickettsii / Q000235:genetics* / Q000276:immunology; D012373:Rocky Mountain Spotted Fever / Q000209:etiology; D012689:Sequence Homology, Nucleic Acid; D012995:Solubility
C100534:190 kDa antigen, Rickettsia; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins