The more the merrier: effects of macromolecular crowding on the structure and dynamics of biological membranes

Abstract

Proteins are essential and abundant components of cellular membranes. Being densely packed within the limited surface area, proteins fulfil essential tasks for life, which include transport, signalling and maintenance of cellular homeostasis. The high protein density promotes nonspecific interactions, which affect the dynamics of the membrane-associated processes, but also contribute to higher levels of membrane organization. Here, we provide a comprehensive summary of the most recent findings of diverse effects resulting from high protein densities in both living membranes and reconstituted systems and display why the crowding phenomenon should be considered and assessed when studying cellular pathways. Biochemical, biophysical and computational studies reveal effects of crowding on the translational mobility of proteins and lipids, oligomerization and clustering of integral membrane proteins, and also folding and aggregation of proteins at the lipid membrane interface. The effects of crowding pervade to larger length scales, where interfacial and transmembrane crowding shapes the lipid membrane. Finally, we discuss the design and development of fluorescence-based sensors for macromolecular crowding and the perspectives to use those in application to cellular membranes and suggest some emerging topics in studying crowding at biological interfaces.

Molecular crowding in single eukaryotic cells: Using cell environment biosensing and single-molecule optical microscopy to probe dependence on extracellular ionic strength, local glucose conditions, and sensor copy number

“…Although many cellular stress responses have been uncovered which use movement and localization of key proteins for signal transduction and genomic control [1,2], the role of physical conditions within the cell, such as macromolecular crowding, is still unclear. Crowding -a local high density of biomolecules that can lead to a weak intermolecular attraction -has been shown to be a key parameter in the function and higher-order structures of proteins and nucleic acids [3] and protein/membrane interactions including aggregate formation [4] and it is therefore also of interest for stress response.…”

Investigating molecular crowding during cell division and hyperosmotic stress in budding yeast with FRET

“…1 ). These dynamic effects have raised new interest in the context of protein aggregation ( Jing et al, 2020 ), intracellular organization ( Löwe et al, 2020 ), and membrane-less compartments in the cytoplasm, for example the formation of liquid-liquid phase separation in the cytoplasm ( Franzmann et al, 2018 ; Jin et al, 2021 ; Park et al, 2020 ). More generally, macromolecular crowding has been linked to a number of biological process such as protein-protein interaction ( Bhattacharya et al, 2013a ), protein conformational changes ( Dong et al, 2010 ), stability and folding ( Despa et al, 2006 ; Stagg et al, 2007 ; Tokuriki, 2004 ), promoting signalling cascades ( Rohwer et al, 1998 ), regulating biomolecular diffusion ( Tabaka et al, 2014 ; Tan et al, 2013 ), and intracellular transport ( Nettesheim et al, 2020 ).…”

Molecular crowding in single eukaryotic cells: using cell environment biosensing and single-molecule optical microscopy to probe dependence on extracellular ionic strength, local glucose conditions, and sensor copy number

“…Although many cellular stress responses have been uncovered which use movement and localization of key proteins for signal transduction and genomic control [1,2], the role of physical conditions within the cell, such as macromolecular crowding, is still unclear. Crowding -weak attraction between macromolecules in close proximity -has been shown to be a key parameter in the function and higher-order structures of proteins and nucleic acids [3] and protein/membrane interactions including aggregate formation [4] and it is therefore also of interest for stress response.…”