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Ca 2+ ‐induced conformational transitions of phosphorylated peptides
Author(s) -
Hollöasi M.,
Ötvös L.,
Ürge L.,
Kajt´ar J.,
Perczel A.,
Laczkó I.,
Vadász ZS.,
Fasman G. D.
Publication year - 1993
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360330316
Subject(s) - chemistry , phosphorylation , biophysics , stereochemistry , biochemistry , biology
CD spectroscopic studies on protected peptides containing lysine and serine, or phosphoserine, and on serine‐containing fragments of the neurofilament protein midsized subunit, both in the unphosphorylated and phosphorylated form, are reported. The introduction of the phosphoryl group was not found to have a significant spectral effect in aqueous solution. In trifluoroethanol (TFE), spectral shifts toward unordered (type U) spectra or the appearance of distorted spectra likely reflect the adoption of aperiodic polypeptide conformations due to salt bridge(s) between negatively charged phosphoserine and positive lysine side‐chain groups. A turn‐stabilizing effect of phosphorylation was also observed. CD‐monitored titration experiments in TFE revealed a high conformational sensitivity of phosphopeptides toward Ca 2+ ions. The appearance of the unordered spectra or spectral shifts were the sign of a bulk disordering effect of Ca 2+ ions. Spectra with specific spectroscopic features reflect the formation of Ca 2+ complexes and the adoption of ordered unique backbone conformations. When ordered structures were obtained on addition of Ca 2+ ions, the observed CD curves showed a resemblance to the spectrum of β‐pleated sheets. This may originate from chain extension and the formation of β‐pleated sheet segments fixed by Ca 2+ bridges between PO 3 H 1 −groups of adjacent peptide chains. The data clearly show that the effect of the Ca 2+ ions is highly specific: the sequence, chain length, presence and distribution of charged side‐chain groups, degree and site of phosphorylation, and environmental factors appear to be determining in the process of chain extension or β‐sheet formation. © 1993 John Wiley & Sons, Inc.