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Surface antigens of the syphilis spirochete and their potential as virulence determinants
D R Blanco1, J N Miller, M A Lovett
1Dept. Microbiology and Immunology, UCLA School of Medicine 90095, USA. dblanco@microimmun.medsch.ucla.edu
Abstract:
A unique physical feature of Treponema pallidum, the venereally transmitted agent of human syphilis, is that its outer membrane contains 100-fold less membrane-spanning protein than the outer membranes of typical gram-negative bacteria, a property that has been related to the chronicity of syphilitic infection. These membrane-spanning T. pallidum rare outer membrane proteins, termed TROMPs, represent potential surface-exposed virulence determinants and targets of host immunity. Only recently has the outer membrane of T. pallidum been isolated and its constituent proteins identified. Five proteins of molecular mass 17-, 28-, 31-, 45-, and 65-kDa were outer membrane associated. The 17- and 45-kDa proteins, which are also present in greater amounts with the T. pallidum inner membrane protoplasmic cylinder complex, had been previously characterized lipoproteins and are, therefore, not membrane-spanning but rather membrane-anchored by their lipid moiety. In contrast, the 28-, 31-, and 65-kDa proteins are exclusively associated with the outer membrane. Both the purified native and an Escherichia coli recombinant outer membrane form of the 31-kDa protein, designated Tromp1, exhibit porin activity, thereby confirming the membrane-spanning outer membrane topology of Tromp1. The 28-kDa protein, designated Tromp2, has sequence characteristics in common with membrane-spanning outer membrane proteins and has also been recombinantly expressed in E. coli, where it targets exclusively to the E. coli outer membrane. The 65-kDa protein, designated Tromp3, is present in the least amount relative to Tromps1 and 2. Tromps 1, 2, and 3 were antigenic when tested with serum from infection and immune syphilitic rabbits and humans. These newly identified TROMPs provide a molecular foundation for the future study of syphilis pathogenesis and immunity.
Insights
Researchers identified novel membrane-spanning proteins in Treponema pallidum, the bacteria causing syphilis. These rare outer membrane proteins (TROMPs) are crucial for understanding syphilis infection and immune responses.
Area of Science:
- Microbiology
- Immunology
- Structural Biology
Background:
- Treponema pallidum, the causative agent of syphilis, possesses a unique outer membrane with significantly fewer membrane-spanning proteins compared to typical Gram-negative bacteria.
- This characteristic is hypothesized to contribute to the chronic nature of syphilitic infections.
- Rare outer membrane proteins (TROMPs) in T. pallidum are potential targets for host immunity and virulence factors.
Purpose of the Study:
- To isolate and identify the proteins present in the outer membrane of T. pallidum.
- To characterize the topology and function of these identified outer membrane proteins.
- To assess the antigenicity of these proteins as potential targets for immune responses against syphilis.
Main Methods:
- Isolation and biochemical analysis of the T. pallidum outer membrane.
- Identification of constituent proteins by molecular mass.
- Recombinant expression of candidate proteins in Escherichia coli to confirm membrane topology and function (e.g., porin activity).
- Antigenicity testing using serum from infected rabbits and humans.
Main Results:
- Five outer membrane-associated proteins were identified with molecular masses of 17, 28, 31, 45, and 65 kDa.
- The 17 and 45 kDa proteins were identified as previously characterized lipoproteins, not membrane-spanning.
- The 28, 31, and 65 kDa proteins (designated Tromp2, Tromp1, and Tromp3, respectively) were exclusively associated with the outer membrane.
- Tromp1 exhibited porin activity, confirming its membrane-spanning nature.
- Tromp2 and Tromp3 also showed characteristics of membrane-spanning proteins and were localized to the outer membrane in E. coli.
- Tromps 1, 2, and 3 were found to be antigenic.
Conclusions:
- The identification of Tromp1, Tromp2, and Tromp3 as exclusively outer membrane-associated, membrane-spanning proteins provides new insights into T. pallidum's unique cell envelope.
- These newly discovered TROMPs are significant as they represent potential targets for the host immune system and play a role in syphilis pathogenesis.
- This study lays the groundwork for future research into syphilis immunity and the development of novel diagnostic and therapeutic strategies.