POLYPEPTIDES OF TREPONEMA-PALLIDUM - PROGRESS TOWARD UNDERSTANDING THEIR STRUCTURAL, FUNCTIONAL, AND IMMUNOLOGICAL ROLES

Treponema pallidum subsp. pallidum, the spirochete that causes syphili s, is unusual in a number of respects, including its small genome size , inability to grow under standard in vitro culture conditions, microa erophilism, apparent paucity of outer membrane proteins, structurally complex periplasmic flagella, and ability to evade the host immune res ponses and cause disease over a period of years to decades. Many of th ese attributes are related ultimately to its protein content. Our know ledge of the activities, structure, and immunogenicity of its proteins has been expanded by the application of recombinant DNA, hybridoma, a nd structural fractionation techniques. The purpose of this monograph is to summarize and correlate this new information by using two-dimens ional gel electrophoresis, monoclonal antibody reactivity, sequence da ta, and other properties as the bases of polypeptide identification. T he protein profiles of the T. pallidum subspecies causing syphilis, ya ws, and endemic syphilis are virtually indistinguishable but differ co nsiderably from those of other treponemal species. Among the most abun dant polypeptides are a group of lipoproteins of unknown function that appear to be important in the immune response during syphilitic infec tion. The periplasmic flagella of T. pallidum and other spirochetes ar e unique with regard to their protein content and ultrastructure, as w ell as their periplasmic location. They are composed of three core pro teins (homologous to the other members of the eubacterial flagellin fa mily) and a single, unrelated sheath protein; the functional significa nce of this arrangement is not understood at present. Although the bac terium contains the chaperonins GroEL and DnaK, these proteins are not under the control of the heat shock regulon as they are in most organ isms. Studies of the immunogenicity of T. pallidum proteins indicate t hat many may be useful for immunodiagnosis and immunoprotection. Futur e goals in T. pallidum polypeptide research include continued elucidat ion of their structural locations and functional activities, identific ation and characterization of the low-abundance outer membrane protein s, further study of the immunoprotective and immunodiagnostic potentia l of T. pallidum proteins, and clarification of the roles of treponema l proteins in pathogenesis.