Alain Brisson

Sub-domain structure of lipid-bound annexin-V resolved by electron image analysis.

Two-dimensional crystals of annexin-V bound to lipid layers containing dioleoylphosphatidylserine have been obtained in the presence of Ca2+. The crystals diffract to 20 A resolution and have the symmetry of the plane group p3 (unit cell dimensions: a = b = 94 A, gamma = 120 degrees). Electron image analysis revealed that the crystals are composed of trimers of annexin-V forming triskelion-like motifs. Each annexin-V molecule has a characteristic elongated shape, about 65 A by 20 A, when observed perpendicularly to the crystal plane. It is composed of two staggered domains of similar size, about 40 A by 20 A. Both domains are made of two sub-domains. The present data suggest that the four resolved sub-domains represent the folding units corresponding to the four 70 amino acid repeating segments characteristic of all annexins.

Automation of specimen selection and data acquisition for protein electron crystallography

Abstract A system is presented for semi-automatic specimen selection and data acquisition for protein electron crystallography, based on a slow-scan CCD camera connected to a transmission electron microscope and control from an external computer. Areas of interest on the specimen are localised at low magnification and subsequently imaged on the CCD camera, using a dose which is small compared to the dose used in the exposure mode. The crystalline quality of the area is evaluated from the appearance of diffraction peaks in the calculated image Fourier transform. If the quality is considered good, images can then be recorded in different modes, both on film and using the CCD camera. Using this system a significant gain, both quantitatively and qualitatively, can be obtained in acquiring data for electron crystallography of beam-sensitive materials.

Structure of soluble and membrane-bound human annexin V

Annexins are a family of water-soluble proteins that bind to membranes in a calcium-dependent manner. Some members have been shown to exhibit voltage-dependent calcium channel activity, a property characteristic of integral membrane proteins. The structures of human annexin V in crystals obtained from aqueous solution and in two-dimensional crystals when bound to phospholipid layers have been determined by X-ray and electron crystallography, respectively. They are compared here. Both structures show close correspondence, suggesting that annexins attach to phospholipid membranes without substantial structural change. These observations, together with biochemical data, lead to the conclusion that annexin V interacts with phospholipid membranes with its convex face. We propose that binding is mediated by direct interaction between the phosphoryl headgroups and the calcium bound to polypeptide loops protruding from the convex face. The membrane area covered by annexin may thus become disordered and permeable allowing calcium flux through the membrane and the central channel-like structure found in annexin molecules.

Self-assembly of the hydrophobin SC3 proceeds via two structural intermediates

Hydrophobins self assemble into amphipathic films at hydrophobic–hydrophilic interfaces. These proteins are involved in a broad range of processes in fungal development. We have studied the conformational changes that accompany the self‐assembly of the hydrophobin SC3 with polarization‐modulation infrared reflection absorption spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, and circular dichroism, and related them to changes in morphology as observed by electron microcopy. Three states of SC3 have been spectroscopically identified previously as follows: the monomeric state, the α‐helical state that is formed upon binding to a hydrophobic solid, and the β‐sheet state, which is formed at the air–water interface. Here, we show that the formation of the β‐sheet state of SC3 proceeds via two intermediates. The first intermediate has an infrared spectrum indistinguishable from that of the α‐helical state of SC3. The second intermediate is rich in β‐sheet structure and has a featureless appearance under the electron microscope. The end state has the same secondary structure, but is characterized by the familiar 10‐nm‐wide rodlets.

Synthesis of Pyridinium Amphiphiles Used for Transfection and Some Characteristics of Amphiphile/DNA Complex Formation

Pyridinium amphiphiles have found practical use for the delivery of DNA into cells. Starting from 4-methylpyridine, a general synthesis has been devised for the production of pyridinium amphiphiles which allows variation in both the hydrophobic part and in the headgroup area of the compounds. By means of differential scanning microcalorimetry, zeta potential, particle size measurements and cryo electron microscopy, some characteristics of the pyridinium amphiphile/ DNA complexes have been determined.

Characterization of the growth of 2D protein crystals on a lipid monolayer by ellipsometry and rigidity measurements coupled to electron microscopy.

We present here some sensitive optical and mechanical experiments for monitoring the process of formation and growth of two-dimensional (2D) crystals of proteins on a lipid monolayer at an air-water interface. The adsorption of proteins on the lipid monolayer was monitored by ellipsometry measurements. An instrument was developed to measure the shear elastic constant (in plane rigidity) of the monolayer. These experiments have been done using cholera toxin B subunit (CTB) and annexin V as model proteins interacting with a monosialoganglioside (GM1) and dioleoylphosphatidylserine (DOPS), respectively. Electron microscopy observations of the protein-lipid layer transferred to grids were systematically used as a control. We found a good correlation between the measured in-plane rigidity of the monolayer and the presence of large crystalline domains observed by electron microscopy grids. Our interpretation of these data is that the crystallization process of proteins on a lipid monolayer passes through at least three successive stages: 1) molecular recognition between protein and lipid-ligand, i.e., adsorption of the protein on the lipid layer; 2) nucleation and growth of crystalline patches whose percolation is detected by the appearance of a non-zero in-plane rigidity; and 3) annealing of the layer producing a slower increase of the lateral or in-plane rigidity.

Two-dimensional crystallization of proteins on lipid monolayers at the air-water interface and transfer to an electron microscopy grid

Abstract The two-dimensional (2-D) crystallization of proteins on lipid monolayers at the air–water interface is a well established method for crystallizing soluble proteins. The transfer of 2-D crystals from the air–water interface to an electron microscopy (EM) grid constitutes a critical and ill-controlled step in the whole procedure, which is likely to be responsible for the high variability of results obtained with this method. In this paper, we address the following questions: (1) does the material observed on EM grids constitute a true representation of the material present at the air–water interface? (2) is there an optimal method of transfer to obtain well-ordered protein 2-D crystals? To answer these questions, we combine data obtained on three different protein systems, annexin V, streptavidin and cholera toxin, using two types of EM grids, coated with either holey carbon films or continuous carbon films. These combined observations help us draw a coherent picture of the state of the interfacial films at the air–water surface and provide new insight into the perturbing influence of the transfer step. The main conclusions are: (1) both annexin V and streptavidin form crystalline monolayers at the air–water interface, which are well preserved when transfer is performed by means of holey carbon films; (2) a major reorganization of the material present at the water surface accompanies transfer with continuous carbon films; the basal monolayer is extensively damaged, transforming into domains and vesicular structures, which do not pre-exist at the water surface; with the three protein systems studied here, these domains are often crystalline; (3) the most striking structural reorganization induced by transfer with continuous carbon films is observed with annexin V, for which the native p6 crystalline assembly is transformed into another crystal form more ordered, with p3 symmetry. It is most probable that these conclusions also apply to other protein 2-D crystals formed by the lipid monolayer method. The recent in situ observation of 2-D crystals of annexin V formed on solid-supported bilayers, by atomic force microscopy, supports our interpretation that monolayers transferred with holey carbon films represent the genuine material pre-exisiting at the air–water interface.

Biological motors: Connecting stalks in V-type ATPase

In all organisms, adenosine triphosphate (ATP) provides metabolic energy for driving energy-dependent processes. It is synthesized and/or utilized by enzymes known as F-type and V-type ATPases, which are small rotary motors. Both types consist of a headpiece, F1 or V1, respectively, which is connected by a stalk region to the membrane-bound part, FO or VO. Electron microscopic analysis of negatively stained particles has revealed a peripheral stalk, or stator, between V1 and VO of the V-type (Na+)ATPase of the thermophilic bacterium Clostridium fervidus, like that in F-type ATPases. We have analysed many more particles and now present a more complete structure of the V-type ATPase stator moiety.

Preparation and properties of arsonolipid containing liposomes

Arsonolipids are analogs of phosphonolipids which have a chemically versatile head group. In preliminary cell culture studies, liposomes composed solely of arsonolipids or of phosholipid-arsonolipid mixtures, demonstrate a specific toxicity against cancer cells (Gortzi et al., unpublished results). The possibility of using such formulations as an alternative of arsenic trioxide with or without combination of other cytostatic agents (encapsulated in their aqueous interior) prompted the investigation of their physicochemical characteristics. Herein we compared the characteristics of arsonolipid containing vesicles with different lipid compositions. Experimental results and morphological observations reveal that non-sonicated formulations have different structures and stability (when both membrane integrity and aggregation are taken into account) depending on the acyl chain length of the arsonolipid. When phospholipids and especially cholesterol are included in their membranes almost all arsonolipids studied produce more stable vesicles. An interesting aspect of these arsonolipid containing vesicles is also their negative surface charge, which may be modulated by mixing phospholipids with arsonolipids. Sonicated vesicles have smaller sizes and profoundly higher stability, especially when containing cholesterol and phosphatidylcholine mixed with arsonolipids. The only exception is that of the arsonolipid with the C(12) acyl chain which was observed to produce long tubes which break down to cubes by sonication. In conclusion, these initial studies demonstrate that sonicated vesicles composed of arsonolipid and phospholipid mixtures mixed with cholesterol posses the stability required to be used as an arsonolipid delivery system. In addition, although cryo-electron microscopy demonstrated that the sonicated vesicles are elliptical in shape, their encapsulation efficiency is not significantly lower than sonicated phospholipid liposomes. Thereby, these vesicles may be also used for the delivery of other drug molecules which can be sufficiently retained in their aqueous interior.

Two-dimensional crystallization of proteins on planar lipid films and structure determination by electron crystallography*

Electron crystallography constitutes a powerful new method for determining the struture of biological macromolecules. This method is best adapted to the study of ordered assemblies of macromolecules, and principally to two‐dimensional (2‐D) crystals of proteins. Obtaining protein 2‐D crystals ordered at high resolution constitutes the major limiting step in the application of this approach. Considerable interest has been raised by the development of a rational method of 2‐D crystallization based on the specific binding of proteins to planar lipid films. The applicability of this method is quasi‐general in the case of soluble proteins. Its basic principles, together with examples taken from work in our group, are presented here.