Matrix metalloproteinase proteolysis of the mycobacterial HSP65 protein as a potential source of immunogenic peptides in human tuberculosis
Massachusetts Supranational Tuberculosis Reference Laboratory; Center for Health Policy and Research; Department of Medicine, Division of Infectious Diseases And Immunology
Medical Subject Headings
Adaptive Immunity; Amino Acid Sequence; Antigens, Bacterial; Bacterial Proteins; Catalytic Domain; Chaperonin 60; Epitopes; Humans; Hydrolysis; Immunomodulation; Isoenzymes; Matrix Metalloproteinase 9; Matrix Metalloproteinase Inhibitors; Matrix Metalloproteinases; Molecular Sequence Data; Mycobacterium tuberculosis; Peptide Fragments; Protease Inhibitors; Recombinant Proteins; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Substrate Specificity; Tuberculosis
Bacterial Infections and Mycoses | Immunology and Infectious Disease
Mycobacterium tuberculosis is the causative agent of human tuberculosis (TB). Mycobacterial secretory protein ESAT-6 induces matrix metalloproteinase (MMP)-9 in epithelial cells neighboring infected macrophages. MMP-9 then enhances recruitment of uninfected macrophages, which contribute to nascent granuloma maturation and bacterial growth. Disruption of MMP-9 function attenuates granuloma formation and bacterial growth. The abundant mycobacterial 65 kDa heat shock protein (HSP65) chaperone is the major target for the immune response and a critical component in M. tuberculosis adhesion to macrophages. We hypothesized that HSP65 is susceptible to MMP-9 proteolysis and that the resulting HSP65 immunogenic peptides affect host adaptive immunity. To identify MMPs that cleave HSP65, we used MMP-2 and MMP-9 gelatinases, the simple hemopexin domain MMP-8, membrane-associated MMP-14, MMP-15, MMP-16 and MMP-24, and glycosylphosphatidylinositol-linked MMP-17 and MMP-25. We determined both the relative cleavage efficiency of MMPs against the HSP65 substrate and the peptide sequence of the cleavage sites. Cleavage of the unstructured PAGHG474L C-terminal region initiates the degradation of HSP65 by MMPs. This initial cleavage destroys the substrate-binding capacity of the HSP65 chaperone. Multiple additional cleavages of the unfolded HSP65 then follow. MMP-2, MMP-8, MMP-14, MMP-15 and MMP-16, in addition to MMP-9, generate the known highly immunogenic N-terminal peptide of HSP65. Based on our biochemical data, we now suspect that MMP proteolysis of HSP65 in vivo, including MMP-9 proteolysis, also results in the abundant generation of the N-terminal immunogenic peptide and that this peptide, in addition to intact HSP65, contributes to the complex immunomodulatory interplay in the course of TB infection.
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Citation: FEBS J. 2011 Sep;278(18):3277-86. doi: 10.1111/j.1742-4658.2011.08244.x. Link to article on publisher's site