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Electrostatic interactions play an essential role in the binding of oleic acid with a-lactalbumin in the HAMLET-like complex: A study using charge-specific chemical modifications

Xie, Yongjing; Min, Soyoung; Harte, Nial P.; Kirk, Hannah; O'Brien, John E.; Voorheis, H. Paul; Svanborg, Catharina LU and Mok, Ken LU (2013) In Proteins 81(1). p.1-17
Abstract
Human a-lactalbumin made lethal to tumor cells (HAMLET) and its analogs are partially unfolded protein-oleic acid (OA) complexes that exhibit selective tumoricidal activity normally absent in the native protein itself. To understand the nature of the interaction between protein and OA moieties, charge-specific chemical modifications of lysine side chains involving citraconylation, acetylation, and guanidination were employed and the biophysical and biological properties were probed. Upon converting the original positively-charged lysine residues to negatively-charged citraconyl or neutral acetyl groups, the binding of OA to protein was eliminated, as were any cytotoxic activities towards osteosarcoma cells. Retention of the positive... (More)
Human a-lactalbumin made lethal to tumor cells (HAMLET) and its analogs are partially unfolded protein-oleic acid (OA) complexes that exhibit selective tumoricidal activity normally absent in the native protein itself. To understand the nature of the interaction between protein and OA moieties, charge-specific chemical modifications of lysine side chains involving citraconylation, acetylation, and guanidination were employed and the biophysical and biological properties were probed. Upon converting the original positively-charged lysine residues to negatively-charged citraconyl or neutral acetyl groups, the binding of OA to protein was eliminated, as were any cytotoxic activities towards osteosarcoma cells. Retention of the positive charges by converting lysine residues to homoarginine groups (guanidination); however, yielded unchanged binding of OA to protein and identical tumoricidal activity to that displayed by the wild-type a-lactalbumin-oleic acid complex. With the addition of OA, the wild-type and guanidinated a-lactalbumin proteins underwent substantial conformational changes, such as partial unfolding, loss of tertiary structure, but retention of secondary structure. In contrast, no significant conformational changes were observed in the citraconylated and acetylated a-lactalbumins, most likely because of the absence of OA binding. These results suggest that electrostatic interactions between the positively-charged basic groups on a-lactalbumin and the negatively-charged carboxylate groups on OA molecules play an essential role in the binding of OA to a-lactalbumin and that these interactions appear to be as important as hydrophobic interactions. Proteins 2013. (c) 2012 Wiley Periodicals, Inc. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
HAMLET, BAMLET, protein-fatty acid complex, electrostatic interaction, charge-specific, chemical modification, lysine, protein unfolding, partially unfolded, folded, a-lactalbumin, oleic acid, oleate
in
Proteins
volume
81
issue
1
pages
1 - 17
publisher
John Wiley & Sons
external identifiers
  • wos:000312551700001
  • scopus:84871132663
ISSN
0887-3585
DOI
10.1002/prot.24141
language
English
LU publication?
yes
id
9a2b3d09-b1e4-45fe-afb3-a86526efcb0f (old id 3400788)
date added to LUP
2013-02-01 07:05:13
date last changed
2019-01-06 07:21:02
@article{9a2b3d09-b1e4-45fe-afb3-a86526efcb0f,
  abstract     = {Human a-lactalbumin made lethal to tumor cells (HAMLET) and its analogs are partially unfolded protein-oleic acid (OA) complexes that exhibit selective tumoricidal activity normally absent in the native protein itself. To understand the nature of the interaction between protein and OA moieties, charge-specific chemical modifications of lysine side chains involving citraconylation, acetylation, and guanidination were employed and the biophysical and biological properties were probed. Upon converting the original positively-charged lysine residues to negatively-charged citraconyl or neutral acetyl groups, the binding of OA to protein was eliminated, as were any cytotoxic activities towards osteosarcoma cells. Retention of the positive charges by converting lysine residues to homoarginine groups (guanidination); however, yielded unchanged binding of OA to protein and identical tumoricidal activity to that displayed by the wild-type a-lactalbumin-oleic acid complex. With the addition of OA, the wild-type and guanidinated a-lactalbumin proteins underwent substantial conformational changes, such as partial unfolding, loss of tertiary structure, but retention of secondary structure. In contrast, no significant conformational changes were observed in the citraconylated and acetylated a-lactalbumins, most likely because of the absence of OA binding. These results suggest that electrostatic interactions between the positively-charged basic groups on a-lactalbumin and the negatively-charged carboxylate groups on OA molecules play an essential role in the binding of OA to a-lactalbumin and that these interactions appear to be as important as hydrophobic interactions. Proteins 2013. (c) 2012 Wiley Periodicals, Inc.},
  author       = {Xie, Yongjing and Min, Soyoung and Harte, Nial P. and Kirk, Hannah and O'Brien, John E. and Voorheis, H. Paul and Svanborg, Catharina and Mok, Ken},
  issn         = {0887-3585},
  keyword      = {HAMLET,BAMLET,protein-fatty acid complex,electrostatic interaction,charge-specific,chemical modification,lysine,protein unfolding,partially unfolded,folded,a-lactalbumin,oleic acid,oleate},
  language     = {eng},
  number       = {1},
  pages        = {1--17},
  publisher    = {John Wiley & Sons},
  series       = {Proteins},
  title        = {Electrostatic interactions play an essential role in the binding of oleic acid with a-lactalbumin in the HAMLET-like complex: A study using charge-specific chemical modifications},
  url          = {http://dx.doi.org/10.1002/prot.24141},
  volume       = {81},
  year         = {2013},
}