title: Structure of SALO, a leishmaniasis vaccine candidate from the sand fly Lutzomyia longipalpis.
abstract: Immunity to the sand fly salivary protein SALO (Salivary Anticomplement of Lutzomyia longipalpis) protected hamsters against Leishmania infantum and L. braziliensis infection and, more recently, a vaccine combination of a genetically modified Leishmania with SALO conferred strong protection against L. donovani infection. Because of the importance of SALO as a potential component of a leishmaniasis vaccine, a plan to produce this recombinant protein for future scale manufacturing as well as knowledge of its structural characteristics are needed to move SALO forward for the clinical path.
  
  
  
  Recombinant SALO was expressed as a soluble secreted protein using Pichia pastoris, rSALO(P), with yields of 1g/L and >99% purity as assessed by SEC-MALS and SDS-PAGE. Unlike its native counterpart, rSALO(P) does not inhibit the classical pathway of complement; however, antibodies to rSALO(P) inhibit the anti-complement activity of sand fly salivary gland homogenate. Immunization with rSALO(P) produces a delayed type hypersensitivity response in C57BL/6 mice, suggesting rSALO(P) lacked anti-complement activity but retained its immunogenicity. The structure of rSALO(P) was solved by S-SAD at Cu-Kalpha to 1.94 Å and refined to Rfactor 17%. SALO is ~80% helical, has no appreciable structural similarities to any human protein, and has limited structural similarity in the C-terminus to members of insect odorant binding proteins. SALO has three predicted human CD4+ T cell epitopes on surface exposed helices.
  
  
  
  The results indicate that SALO as expressed and purified from P. pastoris is suitable for further scale-up, manufacturing, and testing. SALO has a novel structure, is not similar to any human proteins, is immunogenic in rodents, and does not have the anti-complement activity observed in the native salivary protein which are all important attributes to move this vaccine candidate forward to the clinical path.
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Oluwatoyin A
authors.initials: OA
authors.lastname: Asojo
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Alan
authors.initials: A
authors.lastname: Kelleher
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Zhuyun
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Pollet
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Elissa M
authors.initials: EM
authors.lastname: Hudspeth
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Wanderson C
authors.initials: WC
authors.lastname: Rezende
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Mallory Jo
authors.initials: MJ
authors.lastname: Groen
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Seid
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Maha
authors.initials: M
authors.lastname: Abdeladhim
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Shannon
authors.initials: S
authors.lastname: Townsend
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Waldione
authors.initials: W
authors.lastname: de Castro
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Antonio
authors.initials: A
authors.lastname: Mendes-Sousa
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Daniella Castanheira
authors.initials: DC
authors.lastname: Bartholomeu
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Ricardo Toshio
authors.initials: RT
authors.lastname: Fujiwara
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.|Department of Biology, Baylor University, Waco, Texas, United States of America.
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Bottazzi
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.|Department of Biology, Baylor University, Waco, Texas, United States of America.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hotez
authors.affiliation: Sabin Vaccine Institute and Texas Children's Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhan
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Fabiano
authors.initials: F
authors.lastname: Oliveira
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Shaden
authors.initials: S
authors.lastname: Kamhawi
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Jesus G
authors.initials: JG
authors.lastname: Valenzuela
mesh_terms: D000818:Animals; D015870:Gene Expression; D008810:Mice, Inbred C57BL; D010843:Pichia / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011576:Psychodidae / Q000737:chemistry*; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D012471:Salivary Proteins and Peptides / Q000008:administration & dosage / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D011994:Recombinant Proteins; D012471:Salivary Proteins and Peptides