Addressing Biological Problems

Membrane proteins are essential for life. They reside in lipidic membranes that form the boundaries of cells and their compartments. Membrane proteins are highly specialized molecular machineries that provide cellular membranes with unique functions. Cellular membranes peppered with membrane proteins not only separate chemically and physically different environments from each other but also actively create and maintain such differences. As such, they are involved in crucial processes such as energy conversion, signal transduction and amplification, enzymatic activities, molecular transport, anchoring of the cytoskeleton, formation of adhesion and motility. However, understanding how membrane proteins function requires to observe them at work.

Since its invention in 1986 by Gerber, Quate and Binnig, the atomic force microscope (AFM) has evolved into a multifunctional tool membrane protein research. In our research group we develop and employ these multifunctional tools to characterize membrane proteins, protein membranes and living cells. Here, however, we develop high-resolution AFM imaging methods approaching a lateral resolution of ≈1 nm and used them to gather information about the oligomeric state and assembly of membrane proteins and to observe membrane proteins at work.

Addressing Biological Problems

Further reading

Unraveling the pore forming steps of pneumolysin from Streptococcus pneumoniae

Quantifying and identifying two ligand-binding sites while imaging native human membrane receptors by AFM

Directly observing the lipid-dependent self-assembly and pore-forming mechanism of the cytolytic toxin listeriolysin O

Imaging G protein-coupled receptors while quantifying their ligand-binding free-energy landscape

Localizing chemical groups while imaging single native proteins by high-resolution AFM

Multiparametric high-resolution imaging of native proteins by force-distance curve– based AFM

Quantitative imaging of the electrostatic field and potential generated by a transmembrane protein at sub-nanometer resolution

Multi-parametric imaging of biological systems by force-distance curve-based AFM

Nanomechanical properties of proteins and membranes depend on loading rate and electrostatic interactions

High-resolution imaging of 2D outer membrane protein F crystals by atomic force microscopy

Out but not in: β-strands shape the unfolding pathway but not the refolding of the large transmembrane β-barrel protein FhuA

Engineering rotor ring stoichiometries in ATP synthases

Investigating fibrillar aggregates of Tau protein by atomic force microscopy

Gating of the MlotiK1 potassium channel involves large rearrangements of the cyclic nucleotide-binding domains

Structure and function of the glucose PTS transporter from Escherichia coli

Quantifying chemical and physical properties of native membrane proteins at molecular resolution by force-volume AFM

High-resolution atomic force microscopy and spectroscopy of native membrane proteins

Studying collagen self-assembly by time-lapse high-resolution AFM

Human tau isoforms assemble into ribbon-like fibrils that display polymorphic structure and stability

Assessing the structure and function of single biomolecules with scanning transmission electron and atomic force microscopes

pH induced conformational change of the outer membrane protein OmpG reconstituted into native E. coli lipids

The c13 ring from Bacillus TA2.A1 ATP synthase shows an extended diameter due to a special structural region

Conformational adaptability of Redb during DNA annealing and implications for its structural relationship with Rad52

AFM: A nanotool in membrane biology

Vertebrate membrane proteins: Structure, function and insights from biophysical approaches

Atomic force microscopy as a multifunctional molecular toolbox in nanobiotechnology

Strategies to prepare and characterize native protein membranes by AFM

An intermediate step in the evolution of ATPases - a hybrid FO-VO rotor in a bacterial Na+ F1FO ATP synthase

Folding and assembly of proteorhodopsin

Straight GDP-tubulin protofilaments form in the presence of taxol

Atomic force microscopy and spectroscopy of native membrane proteins

The oligomeric state of c rings from cyanobacterial F-ATP synthases varies from 13 to 15

Aminosulfonate modulated pH induced conformational changes in Connexin26 hemichannels

Imaging and detecting molecular interactions of single transmembrane proteins

Structure of the rhodopsin dimer: A working model for G-protein coupled receptors

A new approach to prepare membrane proteins for single molecule AFM imaging

Structural evidence for a constant c11 ring stoichiometry in the sodium F-ATP synthase

The c15 ring of the Spirulina platensis F-ATP synthase: F1/Fo symmetry mismatch is not obligatory

Probing different origins of potential barriers stabilizing the membrane proteins halorhodopsin and bacteriorhodopsin

Atomic force microscopy of biological samples

Observing membrane protein diffusion at subnanometer resolution

Observing structure function and assembly of single proteins by AFM

Biomolecular imaging using atomic force microscopy

Conformational changes in surface structures of isolated Connexin26 gap junctions

Identification and structure of a putative Ca2+-binding domain at the C terminus of AQP1

Imaging the electrostatic potential of transmembrane channels: Atomic probe microscopy of OmpF porin

Sampling the conformational space of membrane protein surfaces with the AFM

The central plug in the reconstituted undecameric c cylinder of a bacterial ATP synthase consists of phospholipids

Subunits constrain stoichiometry of ATP synthase rotor

Bacterial sodium ATP synthase has an undecameric motor

From images to interactions: High-resolution phase imaging in tapping-mode atomic force microscopy

Observing proteins at work with the atomic force microscope

Reversible loss of crystallinity during photobleaching purple membrane

The surface topography of lens MIP supports dual functions

Atomic force microscopy of native purple membrane

Conformational changes, flexibilities and intramolecular forces observed on individual proteins using AFM

Conformations of the rhodopsin third cytoplasmic loop grafted onto bacteriorhodopsin

Proton powered turbine of a plant motor

Unfolding pathways of individual bacteriorhodopsins

Atomic force microscopy: a powerful tool to observe biomolecules at work

Atomic force microscopy: a forceful way with single molecules

Charting the surfaces of purple membrane

Controlled unzipping of a bacterial surface layer with atomic force microscopy

High resolution topographs of the Escherichia coli waterchannel aquaporin Z

Tapping mode atomic force microscopy produces faithful high-resolution images of protein surfaces

Surface structures of native bacteriorhodopsin depend on the molecular packing arrangement in the membrane

pH and voltage induced structural changes of porin OmpF explains channel closure

Electrostatically balanced subnanometer imaging of biological specimens by atomic force microscope

Imaging streptavidin 2D crystals on biotinylated lipid monolayers at high resolution with the atomic force microscope

Surface analysis of the photosystem I complex by electron and atomic force microscopy

Mapping flexible protein domains at subnanometer resolution with the AFM

High-resolution imaging of native biological sample surfaces with scanning probe microscope

Electron and atomic force microscopy of membrane proteins

Structural changes of native membrane proteins monitored at subnanometer resolution with the atomic force microscope

The height of biomolecules measured with the atomic force microscope depends on electrostatic interactions

Adsorption of biological molecules to a solid support for scanning probe microscopy

The bacteriophage ø29 head-tail connector imaged at high resolution with atomic force microscopy

Immuno atomic force microscopy of purple membranes

The c₁₃ ring from Bacillus TA2.A1 ATP synthase shows an extended diameter due to a special structural region

An intermediate step in the evolution of ATPases - a hybrid F_O-V_O rotor in a bacterial Na⁺ F₁F_O ATP synthase

Structural evidence for a constant c₁₁ ring stoichiometry in the sodium F-ATP synthase

The c15 ring of the Spirulina platensis F-ATP synthase: F₁/F_o symmetry mismatch is not obligatory

Identification and structure of a putative Ca²⁺-binding domain at the C terminus of AQP1

**High resolution topographs of the Escherichia coli waterchannel aquaporin Z**

**Conformational change of the hexagonally packed intermediate layer of Deinococcus radiodurans observed with atomic force microscopy**