|1nkf, 30 NMR models ()|
CALCIUM-BINDING PEPTIDE, NMR, 30 STRUCTURES
A 12-residue peptide AcDKDGDGYISAAENH2 analogous to the third calcium-binding loop of calmodulin strongly coordinates lanthanide ions (K = 10(5) M-1). When metal saturated, the peptide adopts a very rigid structure, the same as in the native protein, with three last residues AAE fixed in the alpha-helical conformation. Therefore, the peptide provides an ideal helix nucleation site for peptide segments attached to its C terminus. NMR and CD investigations of peptide AcDKDGDGYISAAEAAAQNH2 presented in this paper show that residues A13-Q16 form an alpha-helix of very high stability when the La3+ ion is bound to the D1-E12 loop. In fact, the lowest estimates of the helix content in this segment give values of at least 80% at 1 degreesC and 70% at 25 degreesC. This finding is not compatible with existing helix-coil transition theories and helix propagation parameters, s, reported in the literature. We conclude, therefore, that the initial steps of helix propagation are characterized by much larger s values, whereas helix nucleation is even more unfavorable than is believed. In light of our findings, thermodynamics of the nascent alpha-helices is discussed. The problem of CD spectra of very short alpha-helices is also addressed.
Alpha-helix nucleation by a calcium-binding peptide loop., Siedlecka M, Goch G, Ejchart A, Sticht H, Bierzyski A, Proc Natl Acad Sci U S A. 1999 Feb 2;96(3):903-8. PMID:9927666
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.