Cyclic peptide models of the Ca2+-binding loop of α-lactalbumin

Viktor Farkas, Elemér Vass, Ignace Hanssens, Zsuzsa Majer, Miklós Hollósi

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

A series of cyclic peptides with different linkers were designed and synthesized to model the elbow-type Ca2+-binding loop of α-lactalbumin (LA). All amino acids of the Ca2+-binding loop are strikingly well conserved among LAs of different species with the sequence Lys79-Phe-Leu-Asp82-Asp-Asp-Leu-Thr- Asp 87-Asp88, where three carboxylates of Asp82, Asp87, and Asp88 and the amide carbonyl oxygen atoms of Lys79 and Asp84 participate in Ca2+ binding. Alanine-containing models were also prepared for monitoring the role of the binding (82, 87-88) and nonbinding Asp residues (83-84) in coordinating the cation. The structural features of synthetic peptides and their Ca 2+-binding properties were investigated in solution by circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy. In water, the CD curves show a strong negative band below 200 nm as a sign of the presence of unfolded conformers. In TFE, all cyclic peptides were found to have a CD spectrum, reflecting the presence of folded (turn) conformers. The effect of Ca2+ was dependent on the structure and concentration of the model and the Ca2+ to peptide ratio (rcat). A surprising time dependence of the FTIR spectra of Ca2+ complexes of the Ala-containing peptides was observed. The shape of the broad amide I band showed no more change after ∼60 min. Contrary to this, the deprotonation of the side chain COOH group(s) and formation of the final coordination sphere of Ca2+ took more time. Infrared spectra showed that in the Ca 2+ complex of model comprising the binding Asp residues of LA, the cation is coordinated to the COO- groups of all three Asps, while in the complex of model comprising nonbinding Asp residues of LA, the two neighboring Asp side chains form a bridged Ca2+-binding system.

Original languageEnglish
Pages (from-to)5310-5320
Number of pages11
JournalBioorganic and Medicinal Chemistry
Volume13
Issue number17
DOIs
Publication statusPublished - Sep 1 2005

Keywords

  • Ca-binding loop
  • Circular dichroism
  • Cyclic peptides
  • FTIR
  • α-Lactalbumin

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Medicine
  • Molecular Biology
  • Pharmaceutical Science
  • Drug Discovery
  • Clinical Biochemistry
  • Organic Chemistry

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