title: Localization of the serine protease homolog BmSPH-1 in nodules of E. coli-injected Bombyx mori larvae and functional analysis of its role in nodule melanization.
abstract: The molecular mechanisms underlying nodule formation and melanization, an important pathogen defense mechanism in insects, are poorly understood. In this study, we investigated the role of BmSPH-1, a catalytically inactive Bombyx mori serine protease homolog, in nodule melanization induced by injection of Escherichia coli cells into the B. mori larval hemocoel. Addition of the melanization substrate L-3,4-dihydroxyphenylalanine (DOPA) to newly formed nodules prompted nodule melanization, confirming that nodules contain activated prophenoloxidase needed for melanization. Immunoprecipitation and immunoblot studies demonstrated that BmSPH-1 interacts with BmLBP, a C-type lectin that binds Gram-negative bacteria, and that BmSPH-1 is present in a truncated, putatively activated form at the E. coli cell surface in nodules. Pretreatment of larvae with anti-BmSPH-1 serum inhibited nodule melanization in E. coli-injected larvae. These results suggest that BmSPH-1 regulates nodule melanization and is recruited into nodules from the hemolymph by BmLBP.
authors.affiliation: Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Koganei 2-24-16, Tokyo 184-8588, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Sakamoto
authors.forename: Masayuki
authors.initials: M
authors.lastname: Ohta
authors.forename: Asahi
authors.initials: A
authors.lastname: Suzuki
authors.forename: Hinako
authors.initials: H
authors.lastname: Takase
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Yoshizawa
authors.forename: Madoka
authors.initials: M
authors.lastname: Kitami
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Sato
mesh_terms: D000818:Animals; D012831:Bombyx / Q000201:enzymology / Q000254:growth & development / Q000276:immunology* / Q000382:microbiology; D004926:Escherichia coli; D006458:Hemolymph / Q000276:immunology; D007814:Larva / Q000201:enzymology / Q000276:immunology / Q000382:microbiology; D008543:Melanins / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000378:metabolism; D057057:Serine Proteases / Q000032:analysis* / Q000378:metabolism
chemical_list: D008543:Melanins; D014442:Monophenol Monooxygenase; D057057:Serine Proteases