Leucine-rich Repeats of Bacterial Surface Proteins Serve as Common Pattern Recognition Motifs of Human Scavenger Receptor gp340
ABSTRACT Scavenger receptors are innate immune molecules recognizing and inducing the clearance of non-host as well as modified host molecules. To recognize a wide pattern of invading microbes, many scavenger receptors bind to common pathogen-associated molecular patterns, such as lipopolysaccharides and lipoteichoic acids. Similarly, the gp340/DMBT1 protein, a member of the human scavenger receptor cysteine-rich protein family, displays a wide ligand repertoire. The peptide motif VEVLXXXXW derived from its scavenger receptor cysteine-rich domains is involved in some of these interactions, but most of the recognition mechanisms are unknown. In this study, we used mass spectrometry sequencing, gene inactivation, and recombinant proteins to identify Streptococcus pyogenes protein Spy0843 as a recognition receptor of gp340. Antibodies against Spy0843 are shown to protect against S. pyogenes infection, but no function or host receptor have been identified for the protein. Spy0843 belongs to the leucine-rich repeat (Lrr) family of eukaryotic and prokaryotic proteins. Experiments with truncated forms of the recombinant proteins confirmed that the Lrr region is needed in the binding of Spy0843 to gp340. The same motif of two other Lrr proteins, LrrG from the Gram-positive S. agalactiae and BspA from the Gram-negative Tannerella forsythia, also mediated binding to gp340. Moreover, inhibition of Spy0843 binding occurred with peptides containing the VEVLXXXXW motif, but also peptides devoid of the XXXXW motif inhibited binding of Lrr proteins. These results thus suggest that the conserved Lrr motif in bacterial proteins serves as a novel pattern recognition motif for unique core peptides of human scavenger receptor gp340.
- SourceAvailable from: V. Wallace McCarlie
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- "When in the planktonic form, SRCRs provide gp340 the ability to serve as a pattern recognition receptor . Thus, gp340 “promotes bacterial aggregation and clearance”  when it encounters S. mutans planktonically. However, when the glycoprotein is embedded in the tooth pellicle or on the epithelium or on microbes themselves (i.e., immobilized in dental biofilm), it instead serves as a receptor for streptococcal attachment . "
ABSTRACT: Bacterial adherence to the acquired dental pellicle, important in dental caries (caries), is mediated by receptor-adhesins such as salivary agglutinin binding to Streptococcus mutans antigen I/II (I/II). Ten selected I/II epitopes were chosen to determine their reactivity to human salivary IgA. Previous studies suggested that a specific HLA biomarker group (HLA-DRB1*04) may have differential influence of immune responses to I/II. However, it was not known whether secretory IgA (SIgA) responses to the selected epitopes from HLA-DRB1*04 positive subjects were different compared to controls, or across other caries-related factors such as total IgA (TIgA). Thirty-two total subjects were matched accord-ing to HLA type, gender, ethnicity and age. HLA genotyping, oral bacterial, immunoglobulin and antibody analyses were performed. A large observed difference emerged with regard to the natural immune reservoir of TIgA in HLA-DRB1*04 positive subjects, specifically, a 27.6% reduction compared to controls. In contrast to all other epitopes studied, HLA-DRB1*04 positive sub-jects also exhibited reduced reactivity to I/II epitope 834-853. HLA-DRB1*04 positive subjects exhibited lower specific SIgA activity/TIgA to 834-853 and also a lower specific reactivity to 834-853/whole cell S. mutans UA159. Further-more, HLA-DRB1*04 positive subjects exhibited lower responses to I/II in its entirety. The large observed difference in TIgA and the 834-853 re-activity pattern across multiple measures suggest potentially important connections pertaining to the link between HLA-DRB1*04 and caries.Open Journal of Immunology 09/2013; 3(3):82-92. DOI:10.4236/oji.2013.33012
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- "SALSA was early on described as an agent that agglutinates Streptococcus mutans, but has since then been shown to bind a broad spectrum of microbes including Gram-positive and -negative bacteria as well as viruses (Ericson and Rundegren, 1983; Nagashunmugam et al., 1998; Prakobphol et al., 2000; Hartshorn et al., 2003; Bikker et al., 2004; Loimaranta et al., 2005; Leito et al., 2008). Part of the wide ligand binding capacity of SALSA is based on its ability to recognize conserved repeat motives on bacterial surface proteins (Loimaranta et al., 2009). A specific peptide sequence motif within the SRCR domains, VEVLXXXXW (X for any amino acid), has been shown to confer bacterial binding (Bikker et al., 2004). "
ABSTRACT: The salivary scavenger and agglutinin (SALSA), also known as gp340, salivary agglutinin and deleted in malignant brain tumor 1, is a 340-kDa glycoprotein expressed on mucosal surfaces and secreted into several body fluids. SALSA binds to a broad variety of microbes and endogenous ligands, such as complement factor C1q, surfactant proteins D and A, and IgA. Our search for novel ligands of SALSA by direct protein-interaction studies led to the identification of mannan-binding lectin (MBL) as a new binding partner. We observed that surface-associated SALSA activates complement via binding of MBL. On the other hand, soluble SALSA was found to inhibit Candida albicans-induced complement activation. Thus, SALSA has a dual complement activation modifying function. It activates the lectin pathway when bound to a surface and inhibits it when free in the fluid phase. These activities are mediated via a direct interaction with MBL. This suggests that SALSA could target the innate immune responses to certain microorganisms and simultaneously limit complement activation in the fluid phase.Frontiers in Immunology 11/2012; 3(11):205. DOI:10.3389/fimmu.2012.00205
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- "As expected, Pam 3 CSK 4 and rBspLRR1 induced NF-jB activity in HEK293 (hTLR2/hTLR1) cells. On the other hand, the recombinant YopM protein of Yersinia entercolitica that belongs to a LRR family different from that of BspA  as well as recombinant glutathione S-transferase protein did not induce NF-jB in TLR2 expressing reporter cell lines (Fig. 2A). Since THP-Blue cells express multiple receptors in addition to TLR2, the specificity of the response was confirmed with the function-blocking monoclonal antibody to TLR2. "
ABSTRACT: Pathogenesis of many bacterially-induced inflammatory diseases is driven by Toll-like receptor (TLR) mediated immune responses following recognition of bacterial factors by different TLRs. Periodontitis is a chronic inflammation of the tooth supporting apparatus often leading to tooth loss, and is caused by a Gram-negative bacterial consortium that includes Tannerella forsythia. This bacterium expresses a virulence factor, the BspA, which drives periodontal inflammation by activating TLR2. The N-terminal portion of the BspA protein comprises a leucine-rich repeat (LRR) domain previously shown to be involved in the binding and activation of TLR2. The objective of the current study was to identify specific epitopes in the LRR domain of BspA that interact with TLR2. Our results demonstrate that a sequence motif GC(S/T)GLXSIT is involved in mediating the interaction of BspA with TLR2. Thus, our study has identified a peptide motif that mediates the binding of a bacterial protein to TLR2 and highlights the promiscuous nature of TLR2 with respect to ligand binding. This work could provide a structural basis for designing peptidomimetics to modulate the activity of TLR2 in order to block bacterially-induced inflammation.Biochemical and Biophysical Research Communications 06/2012; 423(3):577-82. DOI:10.1016/j.bbrc.2012.06.008 · 2.30 Impact Factor