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Microbe-specific C3b deposition in the horseshoe crab complement system in a C2/factor B-dependent or -independent manner.

Tagawa K, Yoshihara T, Shibata T, Kitazaki K, Endo Y, Fujita T, Koshiba T, Kawabata S - PLoS ONE (2012)

Bottom Line: Complement C3 plays an essential role in the opsonization of pathogens in the mammalian complement system, whereas the molecular mechanism underlying C3 activation in invertebrates remains unknown.TtC2/Bf-1 and TtC2/Bf-2 were synthesized and glycosylated in hemocytes and secreted to hemolymph plasma, which existed in a complex with C3 (TtC3), and their activation by microbes was absolutely Mg(2+)-dependent.We conclude that plasma lectins and factor C play key roles in microbe-specific TtC3b deposition in a C2/factor B-dependent or -independent manner.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Systems Life Sciences, Kyushu University, Fukuoka, Japan.

ABSTRACT
Complement C3 plays an essential role in the opsonization of pathogens in the mammalian complement system, whereas the molecular mechanism underlying C3 activation in invertebrates remains unknown. To understand the molecular mechanism of C3b deposition on microbes, we characterized two types of C2/factor B homologs (designated TtC2/Bf-1 and TtC2/Bf-2) identified from the horseshoe crab Tachypleus tridentatus. Although the domain architectures of TtC2/Bf-1 and TtC2/Bf-2 were identical to those of mammalian homologs, they contained five-repeated and seven-repeated complement control protein domains at their N-terminal regions, respectively. TtC2/Bf-1 and TtC2/Bf-2 were synthesized and glycosylated in hemocytes and secreted to hemolymph plasma, which existed in a complex with C3 (TtC3), and their activation by microbes was absolutely Mg(2+)-dependent. Flow cytometric analysis revealed that TtC3b deposition was Mg(2+)-dependent on Gram-positive bacteria or fungi, but not on Gram-negative bacteria. Moreover, this analysis demonstrated that Ca(2+)-dependent lectins (C-reactive protein-1 and tachylectin-5A) were required for TtC3b deposition on Gram-positive bacteria, and that a Ca(2+)-independent lectin (Tachypleus plasma lectin-1) was definitely indispensable for TtC3b deposition on fungi. In contrast, a horseshoe crab lipopolysaccharide-sensitive protease factor C was necessary and sufficient to deposit TtC3b on Gram-negative bacteria. We conclude that plasma lectins and factor C play key roles in microbe-specific TtC3b deposition in a C2/factor B-dependent or -independent manner.

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Schematic domain structures of TtC2/Bf-1 and TtC2/Bf-2.CCP, complement control protein domain; VWF, von Willebrand factor domain; SP, serine protease domain.
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pone-0036783-g001: Schematic domain structures of TtC2/Bf-1 and TtC2/Bf-2.CCP, complement control protein domain; VWF, von Willebrand factor domain; SP, serine protease domain.

Mentions: We identified a homolog of C2/factor B from T. tridentatus with 95.6% sequence identity to CrC2/Bf, designated TtC2/Bf-1 (Figure S1A, database accession no. AB 353280). In addition, we identified another type of C2/factor B, designated TtC2/Bf-2, by a specific set of polymerase chain reaction (PCR) primers for the amplification of the region around the active site His-57 in serine proteases (Figure S1B, database accession no. AB 353281). TtC2/Bf-1 and TtC2/Bf-2 consisted of 864 and 948 amino acid residues, respectively, which were composed of tandem-repeated complement control protein (CCP) domains, a von Willebrand factor (VWF) domain, and a trypsin-type serine protease (SP) domain (Figures 1 and S2). The domain architecture was the same as that of known C2/factor B homologs in mammals. Like CrC2/Bf [6] and sea urchin C2/factor B [8], TtC2/Bf-1 contained five-repeated CCPs (CCP1-CCP5), whereas TtC2/Bf-2 contained seven-repeated CCPs (CCP1-CCP7). The sequence identities between the corresponding domains of the two factors clearly showed that each domain of CCP1-CCP5 of TtC2/Bf-1 had the highest sequence identity to that of CCP3-CCP7 of TtC2/Bf-2 (Table 1). Interestingly, TtC2/Bf-1 contained an extra sequence of approximately 40 amino acids between CCP5 and VWF domains (Figure 1).


Microbe-specific C3b deposition in the horseshoe crab complement system in a C2/factor B-dependent or -independent manner.

Tagawa K, Yoshihara T, Shibata T, Kitazaki K, Endo Y, Fujita T, Koshiba T, Kawabata S - PLoS ONE (2012)

Schematic domain structures of TtC2/Bf-1 and TtC2/Bf-2.CCP, complement control protein domain; VWF, von Willebrand factor domain; SP, serine protease domain.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3351276&req=5

pone-0036783-g001: Schematic domain structures of TtC2/Bf-1 and TtC2/Bf-2.CCP, complement control protein domain; VWF, von Willebrand factor domain; SP, serine protease domain.
Mentions: We identified a homolog of C2/factor B from T. tridentatus with 95.6% sequence identity to CrC2/Bf, designated TtC2/Bf-1 (Figure S1A, database accession no. AB 353280). In addition, we identified another type of C2/factor B, designated TtC2/Bf-2, by a specific set of polymerase chain reaction (PCR) primers for the amplification of the region around the active site His-57 in serine proteases (Figure S1B, database accession no. AB 353281). TtC2/Bf-1 and TtC2/Bf-2 consisted of 864 and 948 amino acid residues, respectively, which were composed of tandem-repeated complement control protein (CCP) domains, a von Willebrand factor (VWF) domain, and a trypsin-type serine protease (SP) domain (Figures 1 and S2). The domain architecture was the same as that of known C2/factor B homologs in mammals. Like CrC2/Bf [6] and sea urchin C2/factor B [8], TtC2/Bf-1 contained five-repeated CCPs (CCP1-CCP5), whereas TtC2/Bf-2 contained seven-repeated CCPs (CCP1-CCP7). The sequence identities between the corresponding domains of the two factors clearly showed that each domain of CCP1-CCP5 of TtC2/Bf-1 had the highest sequence identity to that of CCP3-CCP7 of TtC2/Bf-2 (Table 1). Interestingly, TtC2/Bf-1 contained an extra sequence of approximately 40 amino acids between CCP5 and VWF domains (Figure 1).

Bottom Line: Complement C3 plays an essential role in the opsonization of pathogens in the mammalian complement system, whereas the molecular mechanism underlying C3 activation in invertebrates remains unknown.TtC2/Bf-1 and TtC2/Bf-2 were synthesized and glycosylated in hemocytes and secreted to hemolymph plasma, which existed in a complex with C3 (TtC3), and their activation by microbes was absolutely Mg(2+)-dependent.We conclude that plasma lectins and factor C play key roles in microbe-specific TtC3b deposition in a C2/factor B-dependent or -independent manner.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Systems Life Sciences, Kyushu University, Fukuoka, Japan.

ABSTRACT
Complement C3 plays an essential role in the opsonization of pathogens in the mammalian complement system, whereas the molecular mechanism underlying C3 activation in invertebrates remains unknown. To understand the molecular mechanism of C3b deposition on microbes, we characterized two types of C2/factor B homologs (designated TtC2/Bf-1 and TtC2/Bf-2) identified from the horseshoe crab Tachypleus tridentatus. Although the domain architectures of TtC2/Bf-1 and TtC2/Bf-2 were identical to those of mammalian homologs, they contained five-repeated and seven-repeated complement control protein domains at their N-terminal regions, respectively. TtC2/Bf-1 and TtC2/Bf-2 were synthesized and glycosylated in hemocytes and secreted to hemolymph plasma, which existed in a complex with C3 (TtC3), and their activation by microbes was absolutely Mg(2+)-dependent. Flow cytometric analysis revealed that TtC3b deposition was Mg(2+)-dependent on Gram-positive bacteria or fungi, but not on Gram-negative bacteria. Moreover, this analysis demonstrated that Ca(2+)-dependent lectins (C-reactive protein-1 and tachylectin-5A) were required for TtC3b deposition on Gram-positive bacteria, and that a Ca(2+)-independent lectin (Tachypleus plasma lectin-1) was definitely indispensable for TtC3b deposition on fungi. In contrast, a horseshoe crab lipopolysaccharide-sensitive protease factor C was necessary and sufficient to deposit TtC3b on Gram-negative bacteria. We conclude that plasma lectins and factor C play key roles in microbe-specific TtC3b deposition in a C2/factor B-dependent or -independent manner.

Show MeSH
Related in: MedlinePlus