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alpha-Lactalbumin unfolding is not sufficient to cause apoptosis, but is required for the conversion to HAMLET (human alpha-lactalbumin made lethal to tumor cells).

Svensson, Malin LU ; Fast, Jonas LU ; Mossberg, Anki LU ; Düringer, Caroline LU ; Gustafsson, Lotta LU ; Hallgren, Oskar LU ; Brooks, Charles L.; Berliner, Lawrence; Linse, Sara LU and Svanborg, Catharina LU (2003) In Protein Science 12(12). p.2794-2804
Abstract
HAMLET (human -lactalbumin made lethal to tumor cells) is a complex of human -lactalbumin and oleic acid (C18:1:9 cis) that kills tumor cells by an apoptosis-like mechanism. Previous studies have shown that a conformational change is required to form HAMLET from -lactalbumin, and that a partially unfolded conformation is maintained in the HAMLET complex. This study examined if unfolding of -lactalbumin is sufficient to induce cell death. We used the bovine -lactalbumin Ca2+ site mutant D87A, which is unable to bind Ca2+, and thus remains partially unfolded regardless of solvent conditions. The D87A mutant protein was found to be inactive in the apoptosis assay, but could readily be converted to a HAMLET-like complex in the presence of... (More)
HAMLET (human -lactalbumin made lethal to tumor cells) is a complex of human -lactalbumin and oleic acid (C18:1:9 cis) that kills tumor cells by an apoptosis-like mechanism. Previous studies have shown that a conformational change is required to form HAMLET from -lactalbumin, and that a partially unfolded conformation is maintained in the HAMLET complex. This study examined if unfolding of -lactalbumin is sufficient to induce cell death. We used the bovine -lactalbumin Ca2+ site mutant D87A, which is unable to bind Ca2+, and thus remains partially unfolded regardless of solvent conditions. The D87A mutant protein was found to be inactive in the apoptosis assay, but could readily be converted to a HAMLET-like complex in the presence of oleic acid. BAMLET (bovine -lactalbumin made lethal to tumor cells) and D87A-BAMLET complexes were both able to kill tumor cells. This activity was independent of the Ca2+site, as HAMLET maintained a high affinity for Ca2+ but D87A-BAMLET was active with no Ca2+ bound. We conclude that partial unfolding of -lactalbumin is necessary but not sufficient to trigger cell death, and that the activity of HAMLET is defined both by the protein and the lipid cofactor. Furthermore, a functional Ca2+-binding site is not required for conversion of -lactalbumin to the active complex or to cause cell death. This suggests that the lipid cofactor stabilizes the altered fold without interfering with the Ca2+site. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Protein Science
volume
12
issue
12
pages
2794 - 2804
publisher
The Protein Society
external identifiers
  • wos:000186764600013
  • pmid:14627739
  • scopus:10744223979
ISSN
1469-896X
DOI
10.1110/ps.0231003
language
English
LU publication?
yes
id
5f5f6d98-011d-45d8-9728-f5a50aecaf3b (old id 118791)
alternative location
http://www.proteinscience.org/cgi/content/abstract/12/12/2794
date added to LUP
2007-06-29 14:43:52
date last changed
2018-01-07 05:17:28
@article{5f5f6d98-011d-45d8-9728-f5a50aecaf3b,
  abstract     = {HAMLET (human -lactalbumin made lethal to tumor cells) is a complex of human -lactalbumin and oleic acid (C18:1:9 cis) that kills tumor cells by an apoptosis-like mechanism. Previous studies have shown that a conformational change is required to form HAMLET from -lactalbumin, and that a partially unfolded conformation is maintained in the HAMLET complex. This study examined if unfolding of -lactalbumin is sufficient to induce cell death. We used the bovine -lactalbumin Ca2+ site mutant D87A, which is unable to bind Ca2+, and thus remains partially unfolded regardless of solvent conditions. The D87A mutant protein was found to be inactive in the apoptosis assay, but could readily be converted to a HAMLET-like complex in the presence of oleic acid. BAMLET (bovine -lactalbumin made lethal to tumor cells) and D87A-BAMLET complexes were both able to kill tumor cells. This activity was independent of the Ca2+site, as HAMLET maintained a high affinity for Ca2+ but D87A-BAMLET was active with no Ca2+ bound. We conclude that partial unfolding of -lactalbumin is necessary but not sufficient to trigger cell death, and that the activity of HAMLET is defined both by the protein and the lipid cofactor. Furthermore, a functional Ca2+-binding site is not required for conversion of -lactalbumin to the active complex or to cause cell death. This suggests that the lipid cofactor stabilizes the altered fold without interfering with the Ca2+site.},
  author       = {Svensson, Malin and Fast, Jonas and Mossberg, Anki and Düringer, Caroline and Gustafsson, Lotta and Hallgren, Oskar and Brooks, Charles L. and Berliner, Lawrence and Linse, Sara and Svanborg, Catharina},
  issn         = {1469-896X},
  language     = {eng},
  number       = {12},
  pages        = {2794--2804},
  publisher    = {The Protein Society},
  series       = {Protein Science},
  title        = {alpha-Lactalbumin unfolding is not sufficient to cause apoptosis, but is required for the conversion to HAMLET (human alpha-lactalbumin made lethal to tumor cells).},
  url          = {http://dx.doi.org/10.1110/ps.0231003},
  volume       = {12},
  year         = {2003},
}