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The oviduct is an organ in which a subpopulation of sperm is stored in a reservoir, preserving its fertilizing potential. In porcine, two oviductal proteins have been identified in relation to sperm binding, Annexin A2 and Deleted in Malignant Brain Tumor 1 (DMBT1). DMBT1 is a multifunctional, multidomain glycoprotein, and the characteristics of all of its domains, as well as its carbohydrates, make them candidates for sperm binding. In this work, we challenge sperm for binding to pig oviductal cells on primary culture, after treatment with antibodies specific for the different domains present in DMBT1. Only anti-SRCR antibodies produced inhibition of sperm binding to cells. Thus, SRCR is the main domain in DMBT1 promoted sperm binding to form the reservoir in the oviduct, and this function is probably elicited through the polypeptide itself. Fil: Roldán, María Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina Fil: Teijeiro, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; Argentina Fil: Ruiz Álvarez, Jimena Inés. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; Argentina Fil: Marini, Patricia Estela. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina

Neurotrypsin (NT) is a multi‐domain serine protease of the nervous system with only one known substrate: the large proteoglycan Agrin. NT has seen to be involved in the maintenance/turnover of neuromuscular junctions and in processes of synaptic plasticity in the central nervous system. Roles which have been tied to its enzymatic activity, localized in the C‐terminal serine‐protease (SP) domain. However the purpose of NT's remaining 3–4 scavenger receptor cysteine‐rich (SRCR) domains is still unclear. We have determined the crystal structure of the third SRCR domain of murine NT (mmNT‐SRCR3), immediately preceding the SP domain and performed a comparative structural analysis using homologous SRCR structures. Our data and the elevated degree of structural conservation with homologous domains highlight possible functional roles for NT SRCRs. Computational and experimental analyses suggest the identification of a putative binding region for Ca(2+) ions, known to regulate NT enzymatic activity. Furthermore, sequence and structure comparisons allow to single out regions of interest that, in future studies, might be implicated in Agrin recognition/binding or in interactions with as of yet undiscovered NT partners.

Macrophage receptor with collagenous structure (MARCO) is a Class A Scavenger Receptor (cA-SR) that recognizes and phagocytoses of a wide variety of pathogens. Most cA-SRs that contain a C-terminal Scavenger Receptor Cysteine Rich (SRCR) domain use the proximal collagenous domain to bind ligands. In contrast, for the role of the SRCR domain of MARCO in phagocytosis, adhesion and pro-inflammatory signalling is less clear. The discovery of a naturally-occurring transcript variant lacking the SRCR domain, MARCOII, provided the opportunity to study the role of the SRCR domain of MARCO. We tested whether the SRCR domain is required for ligand binding, promoting downstream signalling, and enhancing cellular adhesion. Unlike cells expressing full-length MARCO, ligand binding was abolished in MARCOII-expressing cells. Furthermore, co-expression of MARCO and MARCOII impaired phagocytic function, indicating that MARCOII acts as a dominant negative variant. Unlike MARCO, expression of MARCOII did not enhance Toll-Like Receptor 2 (TLR2)-mediated pro-inflammatory signalling in response to bacterial stimulation. MARCO-expressing cells were more adherent and exhibited a dendritic-like phenotype, while MARCOII-expressing cells were less adherent and did not exhibit changes in morphology. These data suggest the SRCR domain of MARCO is the key domain in modulating ligand binding, enhancing downstream pro-inflammatory signalling, and MARCO-mediated cellular adhesion.

Many cnidarians engage in a mutualism with endosymbiotic photosynthetic dinoflagellates that forms the basis of the coral reef ecosystem. Interpartner interaction and regulation includes involvement of the host innate immune system. Basal metazoans, including cnidarians have diverse and complex innate immune repertoires that are just beginning to be described. Scavenger receptors (SR) are a diverse superfamily of innate immunity genes that recognize a broad array of microbial ligands and participate in phagocytosis of invading microbes. The superfamily includes subclades named SR-A through SR-I that are categorized based on the arrangement of sequence domains including the scavenger receptor cysteine rich (SRCR), the C-type lectin (CTLD) and the CD36 domains. Previous functional and gene expression studies on cnidarian-dinoflagellate symbiosis have implicated SR-like proteins in interpartner communication and regulation. In this study, we characterized the SR repertoire from a combination of genomic and transcriptomic resources from six cnidarian species in the Class Anthozoa. We combined these bioinformatic analyses with functional experiments using the SR inhibitor fucoidan to explore a role for SRs in cnidarian symbiosis and immunity. Bioinformatic searches revealed a large diversity of SR-like genes that resembled SR-As, SR-Bs, SR-Es and SR-Is. SRCRs, CTLDs and CD36 domains were identified in multiple sequences in combinations that were highly homologous to vertebrate SRs as well as in proteins with novel domain combinations. Phylogenetic analyses of CD36 domains of the SR-B-like sequences from a diversity of metazoans grouped cnidarian with bilaterian sequences separate from other basal metazoans. All cnidarian sequences grouped together with moderate support in a subclade separately from bilaterian sequences. Functional experiments were carried out on the sea anemone Aiptasia pallida that engages in a symbiosis with Symbiodinium minutum (clade B1). Experimental blocking of the SR ligand binding site with the inhibitor fucoidan reduced the ability of S. minutum to colonize A. pallida suggesting that host SRs play a role in host-symbiont recognition. In addition, incubation of symbiotic anemones with fucoidan elicited an immune response, indicating that host SRs function in immune modulation that results in host tolerance of the symbionts.