Post-translational amino acid isomerization: a functionally important D-amino acid in an excitatory peptide.
The post-translational modification of an L- to a D-amino acid has been documented in relatively few gene products, mostly in small peptides under 10 amino acids in length. In this report, we demonstrate that a 46-amino acid polypeptide toxin has one D-phenylalanine at position 44, and that the epimerization from an L-Phe to a D-Phe has a dramatic effect on the excitatory effects of the peptide. In one electrophysiological assay carried out, the D-Phe-containing peptide was extremely potent, whereas the unmodified polypeptide had no biological activity, demonstrating that the chirality of the post-translationally modified amino acid is functionally significant. The peptide toxin analyzed, r11a, belongs to the I-gene superfamily of conotoxins that has four disulfide cross-links. The D-Phe in r11a is at the third amino acid from the C terminus, the same relative position from the C-terminal end as the d-amino acid in omega-agatoxin TK from a spider, an unrelated peptide. Thus, although post-translational amino acid isomerization appears to have no strong specificity for the chemical nature of the amino acid side chain, the few peptides where this modification has been established suggest that there may be favored positions near the N or C terminus that are preferential sites for isomerization to a D-amino acid.
Buczek
Olga
O
Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA.
Yoshikami
Doju
D
Bulaj
Grzegorz
G
Jimenez
Elsie C
EC
Olivera
Baldomero M
BM
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D001681:Biological Assay; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin / Q000737:chemistry; D020916:Conotoxins / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004594:Electrophysiology; D010450:Endopeptidases / Q000737:chemistry; D013058:Mass Spectrometry; D008666:Metalloendopeptidases; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D020033:Protein Isoforms; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011894:Rana pipiens; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors
D000596:Amino Acids; D020916:Conotoxins; D004220:Disulfides; D010455:Peptides; D020033:Protein Isoforms; D010649:Phenylalanine; D010450:Endopeptidases; D002918:Chymotrypsin; D008666:Metalloendopeptidases; C058921:endoproteinase Asp-N; D010100:Oxygen