A 21-kDa surface protein of Mycobacterium leprae binds peripheral nerve laminin-2 and mediates Schwann cell invasion

Abstract

Nerve damage is the hallmark of Mycobacterium leprae infection, which results from M. leprae invasion of the Schwann cell of the peripheral nervous system. We have recently shown that the laminin-2 isoform, specially the G domain of laminin ␣2 chain, on the Schwann cell-axon unit serves as an initial neural target for M. leprae. However, M. leprae surface molecules that mediate bacterial invasion of peripheral nerves are entirely unknown. By using human ␣2 laminins as a probe, a major 28-kDa protein in the M. leprae cell wall fraction that binds ␣2 laminins was identified. After N-terminal amino acid sequence analysis, PCR-based strategy was used to clone the gene that encodes this protein. Deduced amino acid sequence of this M. leprae laminin-binding protein predicts a 21-kDa molecule (ML-LBP21), which is smaller than the observed molecular size in SDS/PAGE. Immunofluorescence and immunoelectron microscopy on intact M. leprae with mAbs against recombinant (r) ML-LBP21 revealed that the protein is surface exposed. rML-LBP21 avidly bound to ␣2 laminins, the rG domain of the laminin-␣2 chain, and the native peripheral nerve laminin-2. The role of ML-LBP21 in Schwann cell adhesion and invasion was investigated by using fluorescent polystyrene beads coated with rML-LBP21. Although beads coated with rML-LBP21 alone specifically adhered to and were ingested by primary Schwann cells, these functions were significantly enhanced when beads were preincubated with exogenous ␣2 laminins. Taken together, the present data suggest that ML-LBP21 may function as a critical surface adhesin that facilitates the entry of M. leprae into Schwann cells.Nerve damage in leprosy results from Mycobacterium leprae invasion of Schwann cell of the peripheral nerves and is responsible for most of the deformity and disability of this disease (1, 2). Although patients can be cured of infection by multidrug therapy, the immunopathological sequelae responsible for the characteristic deformities of leprosy can continue during and even after antimicrobial therapy (3). Such therapeutic intervention has so far prevented only one third of infected individuals from suffering new disabilities (3). Therefore, interventions targeted directly to block the early interaction of M. leprae with peripheral nerve is important for the prevention of nerve infection and subsequent peripheral neuropathy.M. leprae invasion of Schwann cells of the peripheral nervous system represents an early crucial step leading to the nerve damage (1, 2). However, the surface molecules of M. leprae that mediate bacterial binding to and invasion of peripheral nerve are entirely unknown. As an important step toward identifying this invasion process, we have recently established that the laminin-2 isoform, specifically the G domain of laminin ␣2 chain, on the Schwann cell-axon unit serves as an initial neural target of M. leprae (4). Laminins, which consist of ␣, ␤, and ␥ chains, are major matrix proteins of basal laminae and play a crucial role in variety of cellular functions...

Extracellular Mycobacterial DNA-binding Protein 1 Participates in Mycobacterium-Lung Epithelial Cell Interaction through Hyaluronic Acid

“…These results indicate that MDP1 localizes on/in the cell wall as well as intracellular ribosome and membrane fractions. This agrees with previous findings (11,15).…”

“…The expression of MDP1 is up-regulated at the stationary or dormant phases of mycobacterial culture (11,14). MDP1 and its homologues, which have been designated as histone-like protein (14) and laminin-binding protein (LBP) (15), are distributed in all mycobacterial species so far examined (12). These imply that MDP1 plays an important role in both slow growth and dormant/latent infection with mycobacteria.…”

“…It is generally accepted that such histone-like proteins participate functionally in the regulation of gene expression by altering three-dimensional genome structure (33)(34)(35). MDP1 is a presumed mycobacteria-specific histone-like protein, although it localizes on the cell wall, besides inside the cell (11,15). In the present study we have focused on the physiological role of extracellularly occurring MDP1.…”

“…MDP1 exits not only in the cytoplasmic space associated with the 50 S ribosomal subunit and presumably nucleoid but also on the bacterial surface (11,15). Nuclear protein is localized in the cytoplasm, and its primitive roles are to compact the genome and control gene expression.…”

“…This signal eventually triggers inflammation for clearance of necrotic cells (18 -20). Mycobacterium leprae produces LBP, which is a homologue of MDP1, although it lacks DNA-binding activity (15). Instead of DNA-binding activity, LBP interacts with laminin-2 and is considered to be involved in M. leprae invasion into Schwann cells of the peripheral nervous system (15).…”