C1. A new role for chloride in biology

It was widely believed that chloride ions acted as nothing but counter ions for protons during proton pumping in organelles. When we made the first measures of lysosomal chloride using Clensor, we found that it was the most chloride rich organelle of the cell. This high chloride was critical for lysosome function and depleting lysosomal chloride impeded the degradative function of the lysosome, seen in many lysosomal storage diseases.

Chakraborty, K., Leung, K., Krishnan, Y.* "High lumenal chloride in the lysosome is critical for lysosome function." eLife, 2017, 6, e28862. PMID: 28742019

C2. Chemically resolving lysosomes in live cells

We developed a new technology to simultaneously measure two ions in the same organelle, retaining information on the concentrations of both ions with single organelle addressability. We call this technology two-ion measurement or 2-IM. It exploits the principle that organelle populations that are challenging to discriminate based on a single parameter, can be resolved in two dimensions (2D) based on a second independent parameter. We thereby chemically resolve a crucial sub-population of lysosomes in healthy individuals, which is lost in patients with lysosomal diseases. We can also distinguish between different sub-types of Niemann Pick Diseases – a lysosomal storage disease. 2-IM can be applied to diagnosing neurological diseases, assessing disease severity and in screening for potential therapeutics.

Leung, K., Chakraborty, K., Saminathan, A., Krishnan, Y.* “A DNA Nanomachine chemically resolves lysosomes in live cells.” Nature Nanotechnology, 2018, DOI: 10.1038/s41565-018-0318-5. PMID: 30510277

C3. The first example of a potential lysosomal calcium importer

The ability to visualize two analytes with single organelle addressability allowed us to solve a thirty-year problem of quantitatively imaging Ca2+ in acidic organelles. Direct quantitative maps of lysosomal calcium ions in C. elegans as well as in skin fibroblasts of patients with Kufor-Rakeb syndrome led to us identifying ATP13A2 — a known risk gene for Parkinson’s disease—as a potential lysosomal calcium importer.

Narayanaswamy, N., Chakraborty, K., Saminathan, A., Zeichner, E., Leung, K., Devany, J., Krishnan, Y.* “A pH-correctable DNA-based fluorescent reporter for organellar calcium.” Nature Methods, 2019, 16, 95. PMID: 30532082