An extracellular serine protease network coordinates key mechanisms of insect defense against microbial infection. Proteolytic activation of prophenoloxidase (PPO) generates phenoloxidase that catalyzes the production of reactive compounds to sequester and kill invading pathogens and parasites. Proteolytic processing of sp?tzle precursor triggers the Toll pathway, which induces the synthesis of antimicrobial peptides and other defense proteins. In insect vectors of human diseases, initiation and regulation of these protease systems may be disrupted by proteins from the intruders. Knowledge of such protein interactions from biochemical model insects such as Manduca sexta will be useful for understanding and manipulating similar systems in arthropod vectors to interfere with disease transmission. We have discovered a branch of the M. sexta protease network that detects Gram-positive bacteria and fungi and mediates PPO activation. In this network, pathogen recognition receptors bind to microbes and initiate protease pathways for PPO and Toll activation. We have identified a new Sushi-domain protease that may participate in a branch of the pathway responsive to Gram-negative bacterial infection. A positive feedback loop in the protease system controls locality and potency of the defense responses. We plan to extend our research on the PPO activation reaction by examining the initiation and regulation of immune protease pathways.
The specific aims of this project are: 1) Characterization of the pathway initiation by Gram-negative bacteria;2) Elucidation of the positive regulatory mechanisms in the protease system;3) Investigation of the structure, function, and activation of M. sexta PPO.

Public Health Relevance

This research will continue to elucidate the function and regulation of a serine protease network during innate immune responses, which produces phenoloxidase and antimicrobial peptides to entrap and kill parasites that cause malaria and filariasis. The acquired knowledge will be useful for disrupting the transmission of human diseases in vector species.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Vector Biology Study Section (VB)
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Gindhart, Joseph G
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Oklahoma State University Stillwater
Other Basic Sciences
Schools of Earth Sciences/Natur
United States
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Kanost, Michael R; Arrese, Estela L; Cao, Xiaolong et al. (2016) Multifaceted biological insights from a draft genome sequence of the tobacco hornworm moth, Manduca sexta. Insect Biochem Mol Biol 76:118-47
Yang, Fan; Wang, Yang; He, Yan et al. (2016) In search of a function of Manduca sexta hemolymph protease-1 in the innate immune system. Insect Biochem Mol Biol 76:1-10
Hu, Yingxia; Wang, Yang; Deng, Junpeng et al. (2016) The structure of a prophenoloxidase (PPO) from Anopheles gambiae provides new insights into the mechanism of PPO activation. BMC Biol 14:2
He, Yan; Cao, Xiaolong; Zhang, Shuguang et al. (2016) Changes in the Plasma Proteome of Manduca sexta Larvae in Relation to the Transcriptome Variations after an Immune Challenge: Evidence for High Molecular Weight Immune Complex Formation. Mol Cell Proteomics 15:1176-87
Cao, Xiaolong; He, Yan; Hu, Yingxia et al. (2015) The immune signaling pathways of Manduca sexta. Insect Biochem Mol Biol 62:64-74
Zhang, Xiufeng; Zheng, Yun; Cao, Xiaolong et al. (2015) Identification and profiling of Manduca sexta microRNAs and their possible roles in regulating specific transcripts in fat body, hemocytes, and midgut. Insect Biochem Mol Biol 62:11-22
Cao, Xiaolong; Jiang, Haobo (2015) Integrated modeling of protein-coding genes in the Manduca sexta genome using RNA-Seq data from the biochemical model insect. Insect Biochem Mol Biol 62:2-10
He, Yan; Cao, Xiaolong; Li, Kai et al. (2015) A genome-wide analysis of antimicrobial effector genes and their transcription patterns in Manduca sexta. Insect Biochem Mol Biol 62:23-37
Zhang, Xiufeng; He, Yan; Cao, Xiaolong et al. (2015) Phylogenetic analysis and expression profiling of the pattern recognition receptors: Insights into molecular recognition of invading pathogens in Manduca sexta. Insect Biochem Mol Biol 62:38-50
Rao, Xiang-Jun; Cao, Xiaolong; He, Yan et al. (2015) Structural features, evolutionary relationships, and transcriptional regulation of C-type lectin-domain proteins in Manduca sexta. Insect Biochem Mol Biol 62:75-85

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