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Copper(II) complexation by pituitary adenylate cyclase activating polypeptide fragments
T Kowalik-Jankowska1, M Jasionowski, L Lankiewicz
1Faculty of Chemistry, University of Wrocław, Poland. terkow@wchuwr.chem.uni.wroc.pl
Journal of Inorganic Biochemistry
|October 26, 1999
Summary
Pituitary adenylate cyclase activating polypeptide fragments form distinct copper(II) complexes. The peptide sequence and pH influence complex stability and structure, revealing insights into metal-peptide interactions.
Area of Science:
- Biochemistry
- Coordination Chemistry
- Peptide Science
Background:
- Pituitary adenylate cyclase activating polypeptide (PACAP) fragments are biologically relevant peptides.
- Understanding metal-ion interactions with peptides is crucial for biological and medicinal applications.
- Copper(II) ions play significant roles in biological systems and can interact with peptide structures.
Purpose of the Study:
- To investigate the protonation and copper(II) complex stability constants of specific PACAP fragments.
- To elucidate the structural characteristics of copper(II) complexes formed with these peptide fragments.
- To determine the influence of peptide sequence and pH on copper(II) coordination and complex formation.
Main Methods:
- Potentiometric studies to determine protonation and stability constants.
- Spectroscopic techniques including UV-Vis, Circular Dichroism (CD), and Electron Spin Resonance (ESR) for structural analysis.
- Synthesis and characterization of peptide fragments: HSDGI-NH2, TDSYS-NH2, and RKQMAVKKYLAAVL-NH2.
Main Results:
- HSDGI-NH2 forms dimeric complexes (Cu2H-2L2) with glycylglycine-like coordination and imidazole bridging at pH 5-8, transitioning to a monomeric CuH-2L complex at higher pH.
- Aspartic acid at position 3 in HSDGI-NH2 stabilizes the CuH-2L species and limits further nitrogen coordination.
- TDSYS-NH2, with aspartic acid at position 2, forms CuL (2N) complexes, with subsequent deprotonation leading to 3N and 4N complexes at higher pH.
- The tetradecapeptide amide forms exceptionally stable 3N and 4N copper(II) complexes compared to pentaalanine amide.
Conclusions:
- The coordination behavior of copper(II) with PACAP fragments is highly dependent on the peptide sequence and pH.
- Dimeric complex formation can occur, influenced by specific residues like imidazole.
- Amino acid residues, particularly aspartic acid, play a critical role in stabilizing specific copper(II) complexation states and dictating coordination numbers.
- PACAP fragments exhibit unique and stable copper(II) complexation properties relevant to their biological functions.