Conantokin-T, a 21-amino acid peptide which induces sleep-like symptoms in young 
mice was purified from the venom of the fish-hunting cone snail, Conus tulipa. 
The amino acid sequence of the peptide was determined and verified by chemical 
synthesis. The peptide has 4 residues of the modified amino acid, 
gamma-carboxyglutamate (Gla). The sequence of the peptide is: 
Gly-Glu-Gla-Gla-Tyr-Gln-Lys-Met-Leu-Gla-Asn-Leu-Arg-Gla-Ala-Glu-Val-Lys- 
Lys-Asn-Ala-NH2. Conantokin-T inhibits N-methyl-D-aspartate (NMDA) 
receptor-mediated calcium influx in central nervous system neurons. This 
observation suggests that like conantokin-G (a homologous Conus peptide with 
recently identified NMDA antagonist activity) conantokin-T has NMDA antagonist 
activity. A sequence comparison of conantokins-T and -G identifies the 4 Gla 
residues and the N-terminal dipeptide sequence as potential key elements for the 
biological activity of this peptide.