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Cu(II)–protamine interaction. II. The formation and structure of Cu(II) complexes of clupeine YII and of peptides mimicking clupeine N‐terminals
Author(s) -
Salardi Sergio,
Tosi Lucia,
GarnierSuillerot Arlette,
Toniolo Claudio,
Bonora Gian Maria,
Marchiori Fernando
Publication year - 1982
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.360210616
Subject(s) - chemistry , stereochemistry , residue (chemistry) , peptide , chelation , metal , protamine , crystallography , biochemistry , inorganic chemistry , organic chemistry , heparin
The interaction of Cu(II) with the protamine clupeine YII (containing proline at the N‐terminal) and with four peptides (H‐Ala‐Arg‐OMe, H‐Ala‐Arg 2 ‐OMe, H‐Pro‐Arg‐OMe, and H‐Arg 4 ‐Tyr) has been studied by means of absorption, CD, and pH neasurements. The first two peptides mimic clupeine YI and Z N‐terminals; the third, the clupeine YII N‐terminal. At 1:1 molar ratio, clupeine YII yields two complexes: the first (I), at pH 6.6, through coordination via the N‐terminal and the contiguous peptide nitrogen forming a five‐membered chelate; the second (II), at pH 8.5, through the occupancy of the other two corners of the coordination square by amino nitrogens of the lateral chains. These complexes are strictly analogous and occur at the same pH as those formed with clupeine Z. Under the same conditions, all the peptides yield complex I in the first step, although the pH at which this complex is fully defined depends on the number of residues in the chain. It is 8.5 for dipeptides, decreases to 6.5 by the addition of a third residue to the chain, and remains constant when the number of residues is three or more. The amino nitrogens of lateral chains are unable to coordinate to the metal in a second step unless one additional peptide bond lies between the N‐terminal residue and that containing the lateral chain bound to the metal. Thus, H‐Ala‐Arg‐OMe and H‐Pro‐Arg‐OMe form hydroxyl complexes in a second step (pH 11), by deprotonation of one of the water molecules coordinated to the metal; one of the lateral chains of H‐Ala‐Arg 2 ‐OMe is able to coordinate in a second step (pH 8.5), but it is only with H‐Arg 4 ‐Tyr that a second complex (II) is obtained in which two amino nitrogens of lateral chains supersede the oxygens of water molecules in I, at pH 8.5.