title: HAMLET forms annular oligomers when deposited with phospholipid monolayers.
abstract: Recently, the anticancer activity of human α-lactalbumin made lethal to tumor cells (HAMLET) has been linked to its increased membrane affinity in vitro, at neutral pH, and ability to cause leakage relative to the inactive native bovine α-lactalbumin (BLA) protein. In this study, atomic force microscopy resolved membrane distortions and annular oligomers (AOs) produced by HAMLET when deposited at neutral pH on mica together with a negatively charged lipid monolayer. BLA, BAMLET (HAMLET's bovine counterpart) and membrane-binding Peptide C, corresponding to BLA residues 75-100, also form AO-like structures under these conditions but at higher subphase concentrations than HAMLET. The N-terminal Peptide A, which binds to membranes at acidic but not at neutral pH, did not form AOs. This suggests a correlation between the capacity of the proteins/peptides to integrate into the membrane at neutral pH-as observed by liposome content leakage and circular dichroism experiments-and the formation of AOs, albeit at higher concentrations. Formation of AOs, which might be important to HAMLET's tumor toxic action, appears related to the increased tendency of the protein to populate intermediately folded states compared to the native protein, the formation of which is promoted by, but not uniquely dependent on, the oleic acid molecules associated with HAMLET.
authors.affiliation: Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009 Bergen, Norway.
authors.forename: Anne
authors.initials: A
authors.lastname: Baumann
authors.forename: Anja Underhaug
authors.initials: AU
authors.lastname: Gjerde
authors.forename: Ming
authors.initials: M
authors.lastname: Ying
authors.forename: Catharina
authors.initials: C
authors.lastname: Svanborg
authors.forename: Holm
authors.initials: H
authors.lastname: Holmsen
authors.forename: Wilhelm R
authors.initials: WR
authors.lastname: Glomm
authors.forename: Aurora
authors.initials: A
authors.lastname: Martinez
authors.forename: Oyvind
authors.initials: O
authors.lastname: Halskau
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007768:Lactalbumin / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D019301:Oleic Acid / Q000737:chemistry; D009829:Oleic Acids / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D017510:Protein Folding; D053835:Unilamellar Liposomes / Q000737:chemistry*
chemical_list: C560443:BAMLET complex, Bos taurus; C506422:HAMLET complex, human; D009829:Oleic Acids; D010743:Phospholipids; D011108:Polymers; D053835:Unilamellar Liposomes; D019301:Oleic Acid; D007768:Lactalbumin