Researchers from Sinai Health have provided a detailed map looking at the organisation of a living human cell. This provides a new tool for scientists to better understand what happens to cells during disease.
The human body consists of trillions of cells. Within each cell there are different compartments with dedicated functions. In fact, compartmentalisation is a defining characteristic of eukaryotic cells. These specialised compartments, known as organelles, each contain different proteins with specific cellular activities. By identifying which proteins reside in which organelle is important to understand the role of each cellular protein.
Earlier approaches to explore this would first kill the cells before trying to separate the organelles. These approaches, however, only provided an unresolved view of the organisation of a cell. Many intracellular compartments have remained refractory to such approaches. Now, researchers are turning to proximity-dependent biotinylation approaches that can characterise the intracellular environment. One such technique, BioID, uses a mutant biotin ligase that is fused to a protein of interest. When this is expressed in cells, it can biotinylate interacting and proximate proteins. These biotinylated proteins are subsequently purified and identified via mass spectrometry.
The Human Cell Map
In a study, published in Nature, researchers characterised the organisation of the proteome in living human cells. To achieve this, the team used BioID to profile intracellular protein markers (baits) for 32 different cellular compartments. The map was based on 192 subcellular markers and defined the intracellular locations of 4,145 unique proteins in HEK293 cells. The localisation predictions obtained from this technique exceeded the specificity of previous approaches. It also enabled the discovery of crucial proteins at the interface between the outer mitochondrial membrane and the endoplasmic reticulum that are important for mitochondrial homeostasis.
From this dataset, the team created humancellmap.org as a community resource. The resource provides online tools for localisation analysis of BioID data and allows users to compare their own data against predictions made in the Human Cell Map.
This work not only provides a greater understanding of the organisation within the human cell, but researchers can also use it to understand what happens during disease.
Co-first author, Dr. James Knight, expressed:
“Human diseases are typically characterised at the molecular level by proteins with aberrant behaviour that cause the cell to behave in pathological ways. In these situations, proteins will often change where they reside in the cell.
Our research is a first step in addressing this challenge in normal cells and we can use it for comparisons against altered cell states, such as disease conditions, to identify proteins with unexpected localisations that may help us understand a diseased cell better.”
Image credit: By 3drenderings – canva