Proteins are macromolecules, which perform a large variety of functions. Most of them have only a single function, but an increasing number of proteins are being identified as multifunctional. Moonlighting proteins form a special class of multifunctional proteins. They perform multiple autonomous and often unrelated functions without partitioning these functions into different domains of the protein. Striking examples are enzymes, which in addition to their catalytic function are involved in fully unrelated processes such as autophagy, protein transport or DNA maintenance. In this contribution we present an overview of our current knowledge of moonlighting proteins and discuss the significant implications for biomedical and fundamental research.

Important insights into aging have been generated with the genetically tractable and short-lived budding yeast. However, it is still impossible today to continuously track cells by high-resolution microscopic imaging (e.g., fluorescent imaging) throughout their entire lifespan. Instead, the field still needs to rely on a 50-y-old laborious and time-consuming method to assess the lifespan of yeast cells and to isolate differentially aged cells for microscopic snapshots via manual dissection of daughter cells from the larger mother cell. Here, we are unique in achieving continuous and high-resolution microscopic imaging of the entire replicative lifespan of single yeast cells. Our microfluidic dissection platform features an optically prealigned single focal plane and an integrated array of soft elastomer-based micropads, used together to allow for trapping of mother cells, removal of daughter cells, monitoring gradual changes in aging, and unprecedented microscopic imaging of the whole aging process. Using the platform, we found remarkable age-associated changes in phenotypes (e.g., that cells can show strikingly differential cell and vacuole morphologies at the moment of their deaths), indicating substantial heterogeneity in cell aging and death. We envision the microfluidic dissection platform to become a major tool in aging research.

Differential scaling between G1 protein production and cell size dynamics promotes commitment to the cell division cycle in budding yeast.