The PE_PGRS Proteins of Mycobacterium tuberculosis Are Ca2+ Binding Mediators of Host–Pathogen Interaction

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• 作者：Veena C. Yeruva ; Apoorva Kulkarni ; Radhika Khandelwal ; Yogendra Sharma ; Tirumalai R. Raghunand
• 刊名：Biochemistry
• 出版年：2016
• 出版时间：August 23, 2016
• 年：2016
• 卷：55
• 期：33
• 页码：4675-4687
• 全文大小：714K
• 年卷期：0
• ISSN：1520-4995

文摘

The phenomenal success of Mycobacterium tuberculosis (M.tb) as a pathogen is primarily based on its ability to modulate host immune responses. The genome of M.tb encodes multiple immunomodulatory proteins, including several members of the multigenic PE_PPE family of which the PE_PGRS proteins are a subset. Curiously, 56 of the 61 PE_PGRS proteins contain multiple copies of the glycine-rich sequence motif GGXGXD/NXUX, a nonapeptide sequence predicted to bind Cap>2+p>, but the functional significance of these motifs remains a mystery. Here we provide evidence via isothermal titration calorimetry, p>45p>Ca blotting, fluorescence, and circular dichroism spectroscopy that Cap>2+p> binds to the PE_PGRS proteins, PE_PGRS33 (Rv1818c) (10 motifs) and PE_PGRS61 (Rv3653) (one motif). Cap>2+p> was observed not to bind to PE_PGRS8 (Rv0742), which lacks nonapeptide motifs. Using recombinant Mycobacterium smegmatis strains expressing Rv1818c and Rv3653 and the THP-1 macrophage model of infection, we show that the two proteins mediate Cap>2+p>-dependent upregulation of the anti-inflammatory cytokine IL-10, events critical to the pathogenesis of M.tb. Both Rv1818c and Rv3653 interact with TLR2 in a Cap>2+p>-dependent manner, providing a novel mechanistic basis for their immunomodulatory effects. Mutations in the nonapeptide motif of Rv3653 led to compromised Cap>2+p> binding, validating the functional criticality of this motif. This study demonstrates for the first time not only their Cap>2+p> binding properties but also an essential role for Cap>2+p> in the functioning of the M.tb PE_PGRS proteins, opening up the possibility of developing novel anti-tuberculosis therapeutics that inhibit Cap>2+p>–PE_PGRS binding.