Atomic force microscopy of biological samples

Particles in therapeutic protein formulations, Part 1: overview of analytical methods

The presence of particles is a major issue during therapeutic protein formulation development. Both proteinaceous and nonproteinaceous particles need to be analyzed not only due to the requirements of the Pharmacopeias but also to monitor the stability of the protein formulation. Increasing concerns about the immunogenic potential together with new developments in particle analysis make a comparative description of established and novel analytical methods useful. Our review aims to provide a comprehensive overview on analytical methods for the detection and characterization of visible and subvisible particles in therapeutic protein formulations. We describe the underlying theory, benefits, shortcomings, and illustrative examples for quantification techniques, as well as characterization techniques for particle shape, morphology, structure, and identity.

Electron microscopy of specimens in liquid

Imaging samples in liquids with electron microscopy can provide unique insights into biological systems, such as cells containing labelled proteins, and into processes of importance in materials science, such as nanoparticle synthesis and electrochemical deposition. Here we review recent progress in the use of electron microscopy in liquids and its applications. We examine the experimental challenges involved and the resolution that can be achieved with different forms of the technique. We conclude by assessing the potential role that electron microscopy of liquid samples can play in areas such as energy storage and bioimaging.

Analysis of affinity maps of membrane proteins on individual human embryonic stem cells

The heterogeneity found in many cell types has greatly inspired research in single-cell gene and protein profiling for discovering the origin of heterogeneity and its role in cell fate decisions. Among the existing techniques to probe heterogeneity, atomic force microscopy (AFM) utilizes an antibody/ligand-modified tip to explore the distribution of a target membrane protein on individual cells in their native environment. In this paper, we establish a practical model to analyze the data systematically, and attempt the quantification of membrane protein abundance on single cells by taking account issues, such as the level of nonspecific interaction, the probe resolution, and the reproducibility of detecting protein distribution. We demonstrated the application in examining the heterogeneous distribution and the local protein abundance of TRA-1-81 antigen on human embryonic stem (hES) cells at the subcellular level. Heterogeneity in TRA-1-81 expression was also detected at the single cell level, suggesting the presence of subpopulation cells within an undifferentiated hES cell colony. The method provides a platform to unveiling the correlation between heterogeneity of membrane proteins and cell development in a complex cell community.

Investigating a macromolecular complex: the toolkit of methods

Structural biologists studying macromolecular complexes spend considerable effort doing strictly "non-structural" work: investigating the physiological relevance and biochemical properties of a complex, preparing homogeneous samples for structural analysis, and experimentally validating structure-based hypotheses regarding function or mechanism. Familiarity with the diverse perspectives and techniques available for studying complexes helps in the critical assessment of non-structural data, expedites the pre-structural characterization of a complex and facilitates the investigation of function. Here we survey the approaches and techniques used to study macromolecular complexes from various viewpoints, including genetics, cell and molecular biology, biochemistry/biophysics, structural biology, and systems biology/bioinformatics. The aim of this overview is to heighten awareness of the diversity of perspectives and experimental tools available for investigating complexes and of their usefulness for the structural biologist.