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A synthetic hexapeptide designed to resemble a proteinaceous p‐loop nest is shown to bind inorganic phosphate
Author(s) -
Bianchi Antonio,
Giorgi Claudia,
Ruzza Paolo,
Toniolo Claudio,
MilnerWhite E. James
Publication year - 2012
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.24038
Subject(s) - chemistry , phosphate , stereochemistry , peptide , amino acid , affinities , residue (chemistry) , hydrogen bond , binding site , side chain , crystallography , biochemistry , molecule , organic chemistry , polymer
The hexapeptide Ser‐Gly‐Ala‐Gly‐Lys‐Thr has been synthesized and characterized. It was designed as a minimal soluble peptide that would be likely to have the phosphate‐binding properties observed in the P‐loops of proteins that bind the β‐phosphate of GTP or ATP. The β‐phosphate in such proteins is bound by a combination of the side chain ε‐amino group of the lysine residue plus the concavity formed by successive main chain peptide NH groups called a nest, which is favored by the glycines. The hexapeptide is shown to bind HPO 4 2− strongly at neutral pH. The affinities of the various ionized species of phosphate and hexapeptide are analyzed, showing that they increase with pH. It is likely the main chain NH groups of the hexapeptide bind phosphate in much the same way as the corresponding P‐loop atoms bind the phosphate ligand in proteins. Most proteinaceous P‐loops are situated at the N‐termini of α‐helices, and this observation has frequently been considered a key aspect of these binding sites. Such a hexapeptide in isolation seems unlikely to form an α‐helix, an expectation in accord with the CD spectra examined; this suggests that being at the N‐terminus of an α‐helix is not essential for phosphate binding. An unexpected finding about the hexapeptide‐HPO 4 2− complex is that the side chain ε‐amino group of the lysine occurs in its deprotonated form, which appears to bind HPO 4 2− via an N···H‐O‐P hydrogen bond. Proteins 2012. © 2012 Wiley Periodicals, Inc.