Reevaluation of the C3a active site using short synthetic C3a analogues.
In 1980 the C-terminal pentapeptide LGLAR (C3a 73-77) was described (Caporale, L. H. et al. J. Biol. Chem. 1980, 255: 10758) as the minimal sequence inducing a C3a-specific activity. We have synthesized C3a-analogue peptides connected to non-peptidic acyl residues known to potentiate biological activity. Starting from the acylated hexapeptide fluorenylmethoxycarbonyl(Fmoc)-aminohexanoyl(Ahx)-ALGLAR+ ++, a related series of shorter peptides was synthesized. C3a-specific activity was measured as ATP release from guinea pig platelets. Even the tripeptide LAR, acylated with Fmoc-Ahx, exhibited C3a-specific activity. With 0.34% C3a activity, it was even more potent than the native LGLAR sequence which has 0.01% activity. N-terminal extension of the acylated tripeptide LAR by adding one to three alanines increased activity tenfold up to 3.26% (Fmoc-Ahx-AAALAR), while N-terminal addition of three glycine residues (Fmoc-Ahx-GGGLAR) only increased activity to 0.83% of native C3a. Furthermore, a stimulus-specific desensitization could be observed. Fmoc-Ahx-R and Fmoc-Ahx-AR exhibited neither activity nor desensitizing capacity, but the addition of four alanines to the dipeptide AR led to a sequence (Fmoc-Ahx-AAAAAR) with a C3a-specific activity of 0.14%. Even arginine prolonged N-terminally with five glycines (Fmoc-Ahx-GGGGGR) exhibited some C3a-specific activity so that for biological activity only the appropriate presentation of arginine seems to be essential.
Köhl
J
J
Institut für Medizinische Mikrobiologie, Medizinische Hochschule Hannover, FRG.
Casaretto
M
M
Gier
M
M
Karwath
G
G
Gietz
C
C
Bautsch
W
W
Saunders
D
D
Bitter-Suermann
D
D
D000255:Adenosine Triphosphate / Q000097:blood; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D015926:Complement C3a / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000494:pharmacology; D013329:Structure-Activity Relationship
D010455:Peptides; D015926:Complement C3a; D000255:Adenosine Triphosphate