A FAMILY OF SURFACE-EXPOSED PROTEINS OF 20 KILODALTONS IN THE GENUS BORRELIA

Relapsing fever and Lyme disease spirochetes of the genus Borrelia dis play at their surfaces abundant lipoproteins: Vmp proteins in Borrelia hermsii and Osp proteins in Borrelia burgdorferi. Vmp and Osp protein s largely determine serotype specificity, and neutralizing antibodies of infected or immunized animals are directed at them. For the present study, we examined B. hermsii serotype 33, which is unique among stra in HS1 serotypes in the low frequency of switches to other serotypes d uring infections and in vitro cultivation. Failing to clone the comple te vmp33 gene, we accomplished its further characterization by (i) det ermining three partial amino acid sequences, (ii) designing oligonucle otide primers based on these amino acid sequences, (iii) cloning and s equencing the central portion of vmp33, and (iv) using outwardly direc ted primers and the inverse PCR to clone the 5' and 3' ends of the gen e and flanking regions. The transcriptional start site was identified by primer extension analysis. Vmp33 aas a polypeptide of 211 amino aci ds; the three partial amino acid sequences were identified in the open reading frame. Vmp33 was found to be more similar to other 20-kDa Vmp proteins of B. hermsii and to OspC proteins of B. burgdorferi than it was to 35- to 39-kDa Vmp proteins of the same strain. Moreover, OspC proteins were more similar to Vmp33 than they were to OspA, -B, or -D proteins of B. burgdorferi. These sequence similarities were consisten t with Western blot (immunoblot) findings of cross-reactions between V mp33 and OspC with anti-Vmp33 and anti-OspC sera. The promoter for the expressed vmp33 gene was found to be different from the expression si te for other active vmp genes characterized to date. These results ind icate that Vmp33 and other small Vmp's belong with OspC to a genus-wid e family of 20-kDa proteins end that expression of these proteins may be coordinated with expression of other Vmp and Osp proteins in Borrel ia spp.