Crystal Structure of a Complex of Surfactant Protein D (SP-D) and Haemophilus influenzae Lipopolysaccharide Reveals Shielding of Core Structures in SP-D-Resistant Strains

Abstract

T he innate immune proteins surfactant protein D (SP-D) and SP-A are pattern recognition receptors (PRRs) that belong to the superfamily of collagen-containing C-type lectins known as the collectins, which in humans also includes CL-L1, CL-P1, and mannan-binding lectin (1). Collectins can enhance proinflammatory molecules such as cytokines, and reactive oxygen species in phagocytes, by interacting with cell surface receptors or by the scavenging of bacterial molecules (2). As first-line host defense molecules in the lung, SP-D and SP-A target pathogens for neutralization and rapid clearance through interaction with surface carbohydrate structures and promotion of phagocytosis by alveolar macrophages. Bacterial surface lipopolysaccharide (LPS) is a target ligand for immune system defense molecules, and recognition by SP-D of the LPS of various Gram-negative bacterial species, including Escherichia coli (3), Haemophilus influenzae (4, 5), Salmonella enterica serovar Minnesota (3), Bordetella species (6), and Pseudomonas aeruginosa (5), has been previously reported. Many of those studies suggested that lung collectins bind to the LPS core and strongly implicated heptose (Hep) and glucose residues in this binding.H. influenzae is a common cause of human disease worldwide. Serotype b capsular strains cause invasive bacteremic infections such as meningitis and septicemia (7,8), while the more prevalent nonencapsulated or nontypeable H. influenzae strains are a common cause of otitis media (9), sinusitis, conjunctivitis, and acute lower respiratory tract infections. Surface-expressed LPS is involved in each stage of the pathogenesis of infections-colonization of the upper respiratory tract, systemic dissemination, and cytotoxic injury to target tissues (10). Host molecules that recognize the LPS of these organisms are important in limiting pathogenicity. In the newborn and in young infants, innate immune components play a key role in frontline defense against infection, while premature infants have reduced collectin levels and are more susceptible to infection (11).The lipid A region of the LPS of H. influenzae bacteria is linked to a triheptosyl inner core by a single phosphorylated 3-deoxy-Dmanno-oct-2-ulosonic acid (Kdo) moiety. While the LPS glycoform structures and the genetic blueprint for biosynthesis are known for many H. influenzae strains, the oligosaccharides of the exposed LPS outer core provide substantial heterogeneity within and between strains (12, 13), hindering detailed investigation of the interaction with the pulmonary collectins. The structure of the wild-type (WT) H. influenzae strain RM153 (Eagan) LPS (

Serum Surfactant Protein D as a Marker of Asthma Severity

“…In this scenario, the increased surface tension caused by the loss of the surfactant function would oppose the bronchodilatory ability of deep inspirations, which has been demonstrated to decrease with the severity of asthma. 5 The effectiveness of the beneficial effects of lung inflation on airways is dependent on the interdependence between the parenchyma that surrounds and sustains the small airways and the outer airway walls. This is further supported by the significant relationship between serum SP-D levels and functional abnormalities of small airways.…”

Novel expression of a functional trimeric fragment of human SP-A with efficacy in neutralisation of RSV

“…Importantly, comparative to full length recombinant SP-A molecules, trimeric rfhSP-A lacks the majority of the collagen domain and the N-terminal domain and thus has a lower propensity to self-aggregate, and has an increased solubility. The rfhSP-D of the closely related molecule SP-D is a well characterised molecule and has provided a wealth of information about the structure/function relationship of SP-D and mode of calcium-dependent ligand binding (Clark et al, 2016, Clark et al, 2005, Clark et al, 2003, Clark, 2010, Strong et al, 2002, Lin et al, 2010, Knudsen et al, 2007, Roona et al, 2012). Thus, this functional trimeric rfhSP-A may prove a useful reagent for research and has increased potential for development as a therapeutic as compared with full-length recombinant SP-A.…”

“…rfhSP-D contains only the CRD, neck and a short collagenous stalk but lacks the N-terminal domain and the majority of the collagen-like domain. This fragment has been well characterised, structurally and functionally (Clark et al, 2016). Using this molecule, it has been demonstrated that the full collagen domain and N-terminal domain of SP-D are not essential for many of the natural functions of SP-D. For example, rfhSP-D has been shown to be effective in neutralising a range of pathogens including RSV (Clark, 2010, Hickling et al, 1999).…”

Surfactant Protein A Impairs Genital HPV16 Pseudovirus Infection by Innate Immune Cell Activation in A Murine Model

“…The patients underwent the procedure for therapeutic purposes. The recombinant fragment of human SP-D (rfhSP-D), a recombinant trimeric neck/CRD fragment of SP-D, including a short region of the collagen stalk (8 Gly-X-Y) and representing residues 179 to 355, was purified using a bacterial expression system as previously described [49]. The purified rfhSP-D protein was treated for endotoxin by addition of 1/5th of the protein sample volume of pre-washed Polymyxin B-Agarose beads according to manufactures protocol (Merck, Kenilworth, NJ, USA).…”