Structural determinants of salmon calcitonin bioactivity: the role of the Leu-based amphipathic alpha-helix.
Salmon calcitonin (sCT) forms an amphipathic helix in the region 9-19, with the C-terminal decapeptide interacting with the helix (Amodeo, P., Motta, A., Strazzullo, G., Castiglione Morelli, M. A. (1999) J. Biomol. NMR 13, 161-174). To uncover the structural requirements for the hormone bioactivity, we investigated several sCT analogs. They were designed so as to alter the length of the central helix by removal and/or replacement of flanking residues and by selectively mutating or deleting residues inside the helix. The helix content was assessed by circular dichroism and NMR spectroscopies; the receptor binding affinity in human breast cancer cell line T 47D and the in vivo hypocalcemic activity were also evaluated. In particular, by NMR spectroscopy and molecular dynamics calculations we studied Leu(23),Ala(24)-sCT in which Pro(23) and Arg(24) were replaced by helix inducing residues. Compared with sCT, it assumes a longer amphipathic alpha-helix, with decreased binding affinity and one-fifth of the hypocalcemic activity, therefore supporting the idea of a relationship between a definite helix length and bioactivity. From the analysis of other sCT mutants, we inferred that the correct helix length is located in the 9-19 region and requires long range interactions and the presence of specific regions of residues within the sequence for high binding affinity and hypocalcemic activity. Taken together, the structural and biological data identify well defined structural parameters of the helix for sCT bioactivity.
Andreotti
Giuseppina
G
Istituto di Chimica Biomolecolare del Consiglio Nazionale delle Ricerche, Comprensorio Olivetti, Edificio A, 80078 Pozzuoli (Napoli), Italy.
Méndez
Blanca López
BL
Amodeo
Pietro
P
Morelli
Maria A Castiglione
MA
Nakamuta
Hiromichi
H
Motta
Andrea
A
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002116:Calcitonin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002942:Circular Dichroism; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D018003:Receptors, Calcitonin / Q000378:metabolism; D012474:Salmon; D017421:Sequence Analysis; D013329:Structure-Activity Relationship
D018003:Receptors, Calcitonin; D002116:Calcitonin