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Erp, an extracellular protein family specific to mycobacteria
Leila de Mendonça-Lima1, Mathieu Picardeau1, Catherine Raynaud1
1Unité de Génétique Mycobactérienne1, and Unité de Bactériologie Moléculaire et Médicale2, Institut Pasteur, F-75724 Paris Cedex 15, France.
Abstract:
Erp (exported repeated protein) was originally characterized as a virulence factor in Mycobacterium tuberculosis and was thought to be present only in Mycobacterium leprae and members of the TB complex. Here it is shown that Erp is a ubiquitous extracellular protein found in all of the mycobacterial species tested. Erp proteins have a modular organization and contain three domains: a highly conserved amino-terminal domain which includes a signal sequence, a central variable region containing repeats based on the motif PGLTS, and a conserved carboxy-terminal domain rich in proline and alanine. The number and fidelity of PGLTS repeats of the central region differ considerably between mycobacterial species. This region is, however, identical in all of the clinical M. tuberculosis strains tested. In addition, it is shown here that a Mycobacterium smegmatis erp::aph mutant displays altered colony morphology which is complemented by all the Erp orthologues tested. The genome sequence flanking the erp gene includes cell-wall-related ORFs and displays extensive conservation between saprophytic and pathogenic mycobacteria.
Insights
Exported Repeated Protein (Erp) is a widespread extracellular protein in mycobacteria, not limited to pathogenic species. Its modular structure varies in repeat regions, impacting colony morphology in Mycobacterium smegmatis.
Area of Science:
- Microbiology
- Molecular Biology
- Genomics
Background:
- Exported Repeated Protein (Erp) was previously identified as a virulence factor in Mycobacterium tuberculosis.
- Erp was believed to be exclusively present in Mycobacterium leprae and the tuberculosis complex.
- The distribution and function of Erp across diverse mycobacterial species were largely unknown.
Purpose of the Study:
- To investigate the prevalence of Erp across various mycobacterial species.
- To characterize the structural domains and repeat regions of Erp proteins.
- To determine the functional role of Erp in mycobacteria, specifically its impact on colony morphology.
Main Methods:
- Bioinformatic analysis of Erp distribution in sequenced mycobacterial genomes.
- Structural analysis of Erp protein domains, including signal sequence, variable repeat region (PGLTS motif), and C-terminal domain.
- Construction and phenotypic analysis of a Mycobacterium smegmatis erp::aph mutant.
- Complementation studies using Erp orthologues from different species.
Main Results:
- Erp is a ubiquitous extracellular protein found in all tested mycobacterial species, extending beyond pathogenic strains.
- Erp proteins exhibit a conserved modular structure with distinct N-terminal, variable central (PGLTS repeats), and C-terminal domains.
- The number and fidelity of PGLTS repeats vary between species but are conserved in clinical M. tuberculosis strains; the erp::aph mutant shows altered colony morphology, complemented by various Erp orthologues.
Conclusions:
- Erp is a broadly conserved protein across the Mycobacterium genus with significant structural variation in its repeat region.
- Erp plays a role in cell wall-related functions, influencing colony morphology in species like Mycobacterium smegmatis.
- The findings expand the known distribution of Erp and suggest conserved functional roles despite sequence variability.