Proctolin

A proctolin-like peptide is regulated after baculovirus infection and mediates in caterpillar locomotion and digestion

Baculoviruses constitute a large group of invertebrate DNA viruses, predominantly infecting larvae of the insect order Lepidoptera. During a baculovirus infection, the virus spreads throughout the insect body producing a systemic infection in multiple larval tissues, included the central nervous system (CNS). As a main component of the CNS, neuropeptides are small protein-like molecules functioning as neurohormones, neurotransmitters, or neuromodulators. These peptides are involved in regulating animal physiology and behavior and could be altered after baculovirus infection. In this study, we have investigated the effect of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) infection on expression of Spodoptera exigua neuropeptides and neuropeptide-like genes. Expression of the gene encoding a polypeptide that resembles the well-known insect neuropeptide proctolin and named as proctolin-like peptide (PLP), was downregulated in the larval brain following infection and was chosen for further analysis. A recombinant Autographa californica multiple nucleopolyhedrovirus (AcMNPV) overexpressing the C-terminal part of the PLP was generated and used in bioassays using S. exigua larvae to study its influence on the viral infection and insect behavior. AcMNPV-PLP-infected larvae showed less locomotion activity and a reduction in growth compared to larvae infected with wild type AcMNPV or mock-infected larvae. These results are indicative of this new peptide as a neuromodulator that regulates visceral and skeletal muscle contractions and offers a novel effector involved in the behavioral changes during baculovirus infection.

Proctolin, an insect neuropeptide

Synthetic, biological and conformational studies on the insect neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) and some of its analogues are reviewed.

Proctolin: a review with emphasis on insects

The distribution, physiological role, mode of action, and pharmacology of the pentapeptide neuroregulator proctolin are reviewed, with special emphasis on insects. Whereas proctolin is distributed extensively throughout arthropods, its presence in molluscs, annelids, or chordates is not well established. In the arthropods, proctolin acts as a neuromodulator and possibly as a neurohormone. It does not appear to function as a conventional neurotransmitter. Two model proctolinergic systems are highlighted: motor control of the visceral muscles of the locust oviduct and of the skeletal muscles of the locust ovipositor. In these preparations proctolin is a cotransmitter acting to enhance neuromuscular transmission and muscular contraction. The mode of action of proctolin is not well understood, although the second messengers cAMP, phosphatidyl inositol, and calcium have been implicated in various systems. Pharmacologically, the proctolin receptor has been examined with structure/activity studies, and the effects of a variety of amino acid substitutions and deletions of the pentapeptide are described. It is unfortunate that no specific antagonists of the proctolin receptor appear to be available and that no receptor-binding studies have been reported. The prospects are good for advances in our understanding of modulatory mechanisms, since proctolin appears to be emerging as the model for studies of this type.

Proctolin in the post-genomic era: new insights and challenges

Complete understanding of how neuropeptides operate as neuromodulators and neurohormones requires integration of knowledge obtained at different levels of biology, including molecular, biochemical, physiological and whole organism studies. Major advances have recently been made in the understanding of the molecular basis of neuropeptide action in invertebrates by analysis of data generated from sequencing the genomes of several insect species, especially that of Drosophila melanogaster. This approach has quickly led to the identification of genes encoding: (1) novel neuropeptide sequences, (2) neuropeptide receptors and (3) peptidases that might be responsible for the processing and inactivation of neuropeptides. In this article, we review our current knowledge of the biosynthesis, receptor interaction and metabolic inactivation of the arthropod neuropeptide, proctolin, and how the analysis and exploitation of genome sequencing projects has provided new insights.

A review of the involvement of proctolin as a cotransmitter and local neurohormone in the oviduct of the locust, Locusta migratoria

The pentapeptide proctolin, originally identified in the cockroach, has been shown to be widely distributed in many insects and to have a broad range of physiological functions. In the oviduct of the locust, Locusta migratoria, proctolin's role as a neurotransmitter/neuromodulator has been well documented; however, a neurohormonal role in the locust is less certain. This review will examine the various roles of proctolin in locust oviduct contraction and will present evidence that a substance chromatographically, immunologically and physiologically indistinguishable from proctolin is present in the hemolymph of the locust, L. migratoria. This material is concentrated in the plasma, rather than the hemocytes, and is present at concentrations ranging from 0.1 to 0.2nM. This review extends the role of proctolin in insects, and suggests that proctolin may play a neurohormonal role in the locust.