Tuesday, 19 November 2002

This presentation is part of : Display Presentations, Section B. Physiology, Biochemistry, Toxicology, and Molecular Biology

The insect cytokine plasmatocyte spreading peptide (PSP) interacts with its receptor through highly specific domains

Kevin D. Clark1, Aditi Arora2, Stephen F. Garczinski3, Joe W. Crim3, Brian F. Volkman4, and Michael R. Strand1. (1) University of Georgia, Department of Entomology, 420 Biological Sciences, Athens, GA, (2) University of Wisconsin-Madison, Medical Sciences, 4139 Veterinary Medicine, Madison, WI, (3) University of Georgia, Department of Cell Biology, Biological Sciences, Athens, GA, (4) Medical College of Wisconsin, Department of Biochemistry, 8701 Watertown Plank Road, Milwaukee, WI

Plasmatocyte Spreading Peptide (PSP) is a 23 amino acid cytokine that induces a class of insect immune cells called plasmatocytes to spread on foreign surfaces. PSP consists of an unstructured N-terminus (residues 1-6) and a well-defined core (residues 7-23) stabilized by a disulfide bond and a short b-hairpin. Mutagenesis studies have identified several domains critical for activity. These include the cysteines used to form the disulfide bond, charged residues within the b-hairpin and, most importantly, residues Glu1 and Phe3. The structure of Phe3 is essential, as adding a hydroxyl (Tyr), or altering the chirality (D-Phe), or replacing the aromatic ring with a branched aliphatic chain (Val) each destroyed the activity. Activity was partially restored by the addition of a methylene group to Val (to make Leu), whereas removal of a methylene group from Phe (phenyl-Gly) destroyed activity, indicating a branched carbon chain with a methylene spacer as the minimum functional structural motif. We also tested alterations of Glu1 and Asn2. Ala substitutions at Glu1 or Asn2 both increased activity, but a Glu1 deletion eliminated activity, indicating that only the charged N-terminal amine is essential. Mutant peptides lacking activity were assayed for antagonism of wild-type PSP activity. Phe3 substitutions were unable to antagonize PSP, whereas mutants lacking the charged N-terminus were effective. These data suggest that Phe3 is essential for PSP/receptor binding. This Phe3-mediated interaction most likely serves to stabilize the normally unstructured N-terminus and therefore facilitates binding and activation of the receptor by the N-terminal amine.

Species 1: Lepidoptera Noctuidae Pseudoplusia includens (soybean looper)
Keywords: peptide cytokine, structure function

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