title: The Scavenger Receptor SSc5D Physically Interacts with Bacteria through the SRCR-Containing N-Terminal Domain.
abstract: The scavenger receptor cysteine-rich (SRCR) family comprises a group of membrane-attached or secreted proteins that contain one or more modules/domains structurally similar to the membrane distal domain of type I macrophage scavenger receptor. Although no all-inclusive biological function has been ascribed to the SRCR family, some of these receptors have been shown to recognize pathogen-associated molecular patterns (PAMP) of bacteria, fungi, or other microbes. SSc5D is a recently described soluble SRCR receptor produced by monocytes/macrophages and T lymphocytes, consisting of an N-terminal portion, which contains five SRCR modules, and a large C-terminal mucin-like domain. Toward establishing a global common role for SRCR domains, we interrogated whether the set of five SRCR domains of SSc5D displayed pattern recognition receptor (PRR) properties. For that purpose, we have expressed in a mammalian expression system the N-terminal SRCR-containing moiety of SSc5D (N-SSc5D), thus excluding the mucin-like domain likely by nature to bind microorganisms, and tested the capacity of the SRCR functional groups to physically interact with bacteria. Using conventional protein-bacteria binding assays, we showed that N-SSc5D had a superior capacity to bind toEscherichia colistrains RS218 and IHE3034 compared with that of the extracellular domains of the SRCR proteins CD5 and CD6 (sCD5 and sCD6, respectively), and similarE. coli-binding properties as Spα, a proven PRR of the SRCR family. We have further designed a more sensitive, real-time, and label-free surface plasmon resonance (SPR)-based assay and examined the capacity of N-SSc5D, Spα, sCD5, and sCD6 to bind to different bacteria. We demonstrated that N-SSc5D compares with Spα in the capacity to bind toE. coliandListeria monocytogenes, and further that it can distinguish between pathogenicE. coliRS218 and IHE3034 strains and the non-pathogenic laboratoryE. colistrain BL21(DE3). Our work thus advocates the utility of SPR-based assays as sensitive tools for the rapid screening of interactions between immune-related receptors and PAMP-bearing microbes. The analysis of our results suggests that SRCR domains of different members of the family have a differential capacity to interact with bacteria, and further that the same receptor can discriminate between different bacteria strains and species.
authors: i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; IBMC - Instituto de Biologia Molecular e Celular, Porto, Portugal; ICBAS - Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Catarina
authors: C
authors: Bessa Pereira
authors: Institute of Photonics and Electronics of the Czech Academy of Sciences , Prague , Czech Republic.
authors: Markéta
authors: M
authors: Bocková
authors: i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; IBMC - Instituto de Biologia Molecular e Celular, Porto, Portugal.
authors: Rita F
authors: RF
authors: Santos
authors: MRC Human Immunology Unit, Nuffield Department of Clinical Medicine, Weatherall Institute of Molecular Medicine, University of Oxford , Oxford , UK.
authors: Ana Mafalda
authors: AM
authors: Santos
authors: i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; IBMC - Instituto de Biologia Molecular e Celular, Porto, Portugal.
authors: Mafalda
authors: M
authors: Martins de Araújo
authors: i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; IBMC - Instituto de Biologia Molecular e Celular, Porto, Portugal.
authors: Liliana
authors: L
authors: Oliveira
authors: Institute of Photonics and Electronics of the Czech Academy of Sciences , Prague , Czech Republic.
authors: Jiří
authors: J
authors: Homola
authors: i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; IBMC - Instituto de Biologia Molecular e Celular, Porto, Portugal; ICBAS - Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Alexandre M
authors: AM
authors: Carmo
keywords: bacteria; pattern recognition receptors; scavenger receptor cysteine-rich; surface plasmon resonance