Structure-activity relationships of an inhibitory nematode FMRFamide-related peptide, SDPNFLRFamide (PF1), on Ascaris suum muscle.
FMRFamide-related peptides are widespread among the Nematoda. Among them is a family of extended PNFLRFamide peptides encoded on the flp-1 peptide precursor gene in Caenorhabditis elegans. The most studied peptide from this series is SDPNFLRFamide (PF1). Each residue in this peptide was sequentially substituted with either alanine or the corresponding d-isomer of the native amino acid in order to define structure-function relationships in this peptide using an Ascaris suum muscle tension assay. In general, substitutions in the N-terminal tetrapeptide had only minor consequences for efficacy, while substitutions in the C-terminal tetrapeptide caused more dramatic changes. Such substitutions typically markedly diminished efficacy, but d-isomer substitution at either position 5 (Phe) or 6 (Leu) converted the inhibitory activity of the prototype into excitation. In addition, it has been evident that KPNFLRFamide and SDPNFLRFamide, though encoded on flp-1 and sharing a PNFLRFamide hexapeptide, act through different receptors. KPNFLRFamide directly gates a chloride channel in A. suum muscle cells, while SDPNFLRFamide acts through nitric oxide synthase to open K+ channels in the same tissue. The use of K+ channel blockers and nitric oxide synthase inhibitors in electrophysiological experiments employing A. suum muscle membranes allowed the unambiguous conclusion that the N-terminal lysine is absolutely required for activation of the chloride channel and excludes interaction with the SDPNFLRFamide receptor.
Bowman
Jerry W
JW
Pharmacia Animal Health, 7000 Portage Road, Kalamazoo, MI 49001-0199, USA.
Friedman
Alan R
AR
Thompson
David P
DP
Maule
Aaron G
AG
Alexander-Bowman
Susan J
SJ
Geary
Timothy G
TG
D000818:Animals; D017165:Ascaris suum / Q000187:drug effects* / Q000502:physiology; D018118:Chloride Channels / Q000378:metabolism; D019835:FMRFamide / Q000737:chemistry / Q000494:pharmacology*; D015801:Helminth Proteins / Q000737:chemistry / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D013329:Structure-Activity Relationship
D018118:Chloride Channels; D015801:Helminth Proteins; D010446:Peptide Fragments; D015221:Potassium Channels; C086748:SDPNFLRFamide; D019835:FMRFamide