Chain Packing in the Inverted Hexagonal Phase of Phospholipids:  A Study by X-ray Anomalous Diffraction on Bromine-labeled Chains

Pan, Deng; Wang, Wangchen; Liu, Wenhan; Yang, Lin; Huang, Huey W.

doi:10.1021/ja058045t

Cited by 31 publications

(47 citation statements)

References 46 publications

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“…We have extensive experience in using the Br-MAD method to solve the structures of lipid phases, including a hexagonal phase (56), a distorted hexagonal phase (57), two different transmembrane pore structures in the R phase (38,41), and the structure of a prestalk intermediate state of membrane fusion in a tetragonal phase (58). To solve the phase problems for these structures, we have made use of the Patterson function (38,56,57), the swelling method (41), and modeling methods (38,56,57). Through this experience, we have realized that we could have chosen the correct phases by examining all the possible phase combinations and obtained the same results.…”

Section: Methodsmentioning

confidence: 99%

Process of inducing pores in membranes by melittin

Lee

Sun

Hung

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Melittin is a prototype of the ubiquitous antimicrobial peptides that induce pores in membranes. It is commonly used as a molecular device for membrane permeabilization. Even at concentrations in the nanomolar range, melittin can induce transient pores that allow transmembrane conduction of atomic ions but not leakage of glucose or larger molecules. At micromolar concentrations, melittin induces stable pores allowing transmembrane leakage of molecules up to tens of kilodaltons, corresponding to its antimicrobial activities. Despite extensive studies, aspects of the molecular mechanism for pore formation remain unclear. To clarify the mechanism, one must know the states of the melittin-bound membrane before and after the process. By correlating experiments using giant unilamellar vesicles with those of peptide-lipid multilayers, we found that melittin bound on the vesicle translocated and redistributed to both sides of the membrane before the formation of stable pores. Furthermore, stable pores are formed only above a critical peptide-to-lipid ratio. The initial states for transient and stable pores are different, which implies different mechanisms at low and high peptide concentrations. To determine the lipidic structure of the pore, the pores in peptide-lipid multilayers were induced to form a lattice and examined by anomalous X-ray diffraction. The electron density distribution of lipid labels shows that the pore is formed by merging of two interfaces through a hole. The molecular property of melittin is such that it adsorbs strongly to the bilayer interface. Pore formation can be viewed as the bilayer adopting a lipid configuration to accommodate its excessive interfacial area.toroidal pore | oriented circular dichroism | rhombohedral phase M elittin, the major toxin of the bee venom discovered around 1970 (1), produces a variety of effects on nature membranes, including cell lysis (2), antimicrobial activity (3), and voltage-dependent ion conductance (4). A great number of hostdefense antimicrobial peptides (5, 6) discovered in the past three decades have been found to exhibit similar behavior of melittin (3, 7). Among membrane-active peptides, melittin is perhaps the most extensively studied (8-12). It is widely used for cell and liposome lysis and as a model for pore-forming peptides (7, 13). Its whole and partial amino acid sequences have been incorporated in the designs of synthetic proteins to mimic the property of melittin (14, 15). However, its molecular process and mechanism of activities are still in dispute. It is clear that melittin binds to membranes as monomers but acts on the membrane collectively. Even at concentrations as low as a few nanomoles per liter, melittin can induce transient pores that allow transmembrane conduction of atomic ions but not leakage of glucose or larger molecules (4,7,16). In the micromolar range, melittin induces stable pores allowing transmembrane leakage of molecules up to tens of kilodaltons (13,17,18). At even higher concentrations, it can act as a detergent disin...

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Section: Methodsmentioning

confidence: 99%

Process of inducing pores in membranes by melittin

Lee

Sun

Hung

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

302

380

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“…S1 and SI Text), is much less clear because of the limited resolution for a complex composition; most notably the peptides are not identifiable (28). This method has been successfully applied to many other lipid systems (28,30,44,45).…”

Section: Methodsmentioning

confidence: 99%

Structure of transmembrane pore induced by Bax-derived peptide: Evidence for lipidic pores

Qian

Wang

Yang

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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203

178

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The structures of transmembrane pores formed by a large family of pore-forming proteins and peptides are unknown. These proteins, whose secondary structures are predominantly ␣-helical segments, and many peptides form pores in membranes without a crystallizable protein assembly, contrary to the family of ␤-pore-forming proteins, which form crystallizable ␤-barrel pores. Nevertheless, a protein-induced pore in membranes is commonly assumed to be a protein channel. Here, we show a type of peptide-induced pore that is not framed by a peptide structure. Peptide-induced pores in multiple bilayers were long-range correlated into a periodically ordered lattice and analyzed by X-ray diffraction. We found the pores induced by Bax-derived helical peptides were at least partially framed by a lipid monolayer. Evidence suggests that the formation of such lipidic pores is a major mechanism for ␣-poreforming proteins, including apoptosis-regulator Bax.antimicrobial peptides ͉ colicins ͉ proapoptotic Bax ͉ the barrel-stave model ͉ the toroidal model P ore-forming proteins and peptides are water soluble but also capable of spontaneously inserting into membranes and making stable transmembrane pores. These proteins and peptides have attracted a great deal of interest for their ability to regulate molecular transport across membranes, for their unusual sequence-structure relationships, and for biotechnological applications (1). Among the large number of pore-forming proteins discovered so far (2-4), those that have been investigated fall into 2 distinct classes. One class , whose secondary structures are predominantly ␤-sheets, form crystallizable porinlike transmembrane ␤-barrel pores. Another class, whose secondary structures are predominantly ␣-helical segments, and all of the known antimicrobial peptides (5) form pores without a crystallizable protein assembly (6). The pore structures for this latter class ␣-pore-forming proteins (␣-PFPs) have long been a puzzle, because unlike ␤-strands, ␣-helices cannot hydrogenbond side-by-side to form a bonded barrel structure. The most common assumption is that ␣-helical segments form a transmembrane barrel-stave assembly stabilized by hydrophobic interactions (7,8). However there has been experimental evidence suggesting another type of pores whose walls were partially lined by lipid head groups rather than framed by a purely proteinaceous structure. Here, we present X-ray diffraction results confirming both types of pore structures induced by helical peptides. Significantly, the formation of lipidic pores is expected to be a common mechanism for ␣-PFPs including apoptosisregulating proteins.The best known ␤-pore-forming proteins are bacterial toxins, e.g., staphylococcal ␣-hemolysin (9). An increasing number of them have been crystallized and imaged in their prepore and pore forms (2-4). On the contrary, none of ␣-pore-forming toxins, such as colicins (10) and diphtheria toxin (11), have ever been crystallized in their pore forms. The class of ␣-PFPs now includes the Bcl-2 family of apo...

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“…For the H II and H IIδ phases, we refer to e.g. [119,136]. In case of DOPC and DPhPC, the existence of the rhombohedral phase was known from the literature [30,51,137].…”

Section: Characteristic Diffraction Patternsmentioning

confidence: 99%

“…In case of the inverted hexagonal phase H II , several authors have quantitatively analyzed electron density data to study elastic deformations of the water cylinders and chain packing [136,189,190]. To the very best of our knowledge, no comparable attempts exist in case of the stalk phase.…”

Section: Electron Density Isosurface Analysis 621 Motivationmentioning

confidence: 99%

Stalk structures in lipid bilayer fusion studied by x-ray diffraction

Aeffner¹

2012

Göttingen Series in X-Ray Physics

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Chain Packing in the Inverted Hexagonal Phase of Phospholipids: A Study by X-ray Anomalous Diffraction on Bromine-labeled Chains

Cited by 31 publications

References 46 publications

Process of inducing pores in membranes by melittin

Process of inducing pores in membranes by melittin

Structure of transmembrane pore induced by Bax-derived peptide: Evidence for lipidic pores

Stalk structures in lipid bilayer fusion studied by x-ray diffraction

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