Camstatins are peptide antagonists of calmodulin based upon a conserved structural motif in PEP-19, neurogranin, and neuromodulin.
Unbridled increases in intracellular ionized calcium can result in neuronal damage and death. Since many of the deleterious effects of calcium are mediated by calmodulin, we have sought to identify neuronal proteins that inhibit activation of this ubiquitous protein. PEP-19 is a 7.6-kDa neuron-specific protein, which contains a motif similar to the calmodulin binding domains of neuromodulin (GAP-43) and neurogranin (RC3). Here we show that PEP-19 binds calmodulin in an analogous calcium-independent manner with an apparent Kd near 1.2 microM. Furthermore, using the calmodulin-dependent enzyme neuronal nitric oxide synthase, we demonstrate that native PEP-19 is also an antagonist of enzyme activity. Based on the PEP-19 sequence, a series of peptide calmodulin antagonists termed camstatins were synthesized. These analogs define the minimally active domain of PEP-19 and provide a structure/activity relationship for calmodulin antagonism. There was a positive correlation between the binding affinities of the camstatins for calmodulin and their potencies as neuronal nitric oxide synthase inhibitors. Despite the similar IQ motif in PEP-19 and neuromodulin or neurogranin, PEP-19 was not a substrate for protein kinase C. The properties of PEP-19 suggest that it could fulfill a role in neuroprotection.
Slemmon
J R
JR
Department of Biochemistry, University of Rochester Medical Center, Rochester, New York 14642, USA.
Morgan
J I
JI
Fullerton
S M
SM
Danho
W
W
Hilbush
B S
BS
Wengenack
T M
TM
D000595:Amino Acid Sequence; D000818:Animals; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D002148:Calmodulin-Binding Proteins / Q000737:chemistry*; D002417:Cattle; D002531:Cerebellum / Q000378:metabolism; D002850:Chromatography, Gel; D017124:Conserved Sequence; D019922:GAP-43 Protein; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000737:chemistry*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D051579:Neurogranin; D019001:Nitric Oxide Synthase / Q000302:isolation & purification / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D013329:Structure-Activity Relationship
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D019922:GAP-43 Protein; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D010455:Peptides; D051579:Neurogranin; D019001:Nitric Oxide Synthase; D011493:Protein Kinase C