title: Degradation-resistant protein domains limit host cell processing and immune detection of mycobacteria.
abstract: The Mycobacterium tuberculosis genome reveals a large family of glycine-alanine rich PE-PGRS proteins. Due to similarities with the glycine-alanine rich Epstein-Barr nuclear antigen 1, there has been interest in whether PE-PGRS proteins inhibit cellular processing and presentation via the major histocompatibility complex class I pathway. We investigated whether PE-PGRS proteins were resistant to ubiquitin-proteasome-dependent degradation and CD8(+) T cell recognition. Upon transient expression of ubiquitin fusion constructs of either full-length Rv0978c(PE-PGRS) protein or its PE domain in HeLa cells, the former was markedly less susceptible to proteasomal degradation. When peptides of varying glycine and alanine content from different PE-PGRS proteins were fused to the N-terminus of SIINFEKL peptide, the alanine-rich fusions elicited lower interleukin-2 responses in SIINFEKL-specific CD8(+) T cells, with corresponding decrease in lysis of cells presenting such peptides. When CD8(+) T cells from Mycobacterium bovis BCG-immunized mice were stimulated with either full-length PE-PGRS protein Rv3812 or its PE domain, the former exhibited a lower level of cytotoxicity against BCG-infected autologous macrophages. These results suggest that mycobacterium PE-PGRS proteins have domains that confer resistance to ubiquitin-proteasome-dependent protein degradation, and the bacteria may have an abundance of such proteins to evade immune detection and killing of mycobacterium-infected cells.
authors.affiliation: Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Kah Wee
authors.initials: KW
authors.lastname: Koh
authors.forename: Norbert
authors.initials: N
authors.lastname: Lehming
authors.forename: Geok Teng
authors.initials: GT
authors.lastname: Seah
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D003001:Cloning, Molecular; D049452:Green Fluorescent Proteins / Q000235:genetics; D006367:HeLa Cells; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000276:immunology; D006801:Humans; D007108:Immune Tolerance / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009169:Mycobacterium tuberculosis / Q000276:immunology* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000235:genetics* / Q000276:immunology / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics* / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics
chemical_list: D011993:Recombinant Fusion Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex