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by Eran Hodis
Green fluorescent protein (GFP) is a bioluminescent polypeptide isolated from the jellyfish Aequorea victoria. GFP converts the blue chemiluminescence of aequorin into green fluorescent light. In the laboratory, GFP can be incorporated into a variety of biological systems in order to function as a marker protein. Since its discovery in 1962, GFP has become a significant contributor to the research of monitoring gene expression, localization, mobility, traffic, or interactions between various membrane and cytoplasmic proteins.

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Y Gu, V Srikanth, AI Salazar-Morales, R Jain, JP O'Brien, SM Yi, RK Soni, FA Samatey, SE Yalcin, NS Malvankar. Nature 2021 doi: 10.1038/s41586-021-03857-w
Geobacter pili were long thought to be electrically conductive protein nanowires composed of PilA-N. Nanowires are crucial to the energy metabolism of bacteria flourishing in oxygen-deprived environments. To everyone's surprise, in 2019, the long-studied nanowires were found to be linear polymers of multi-heme cytochromes, not pili. The first cryo-EM structure of pili (2021) reveals a filament made of dimers of PilA-N and PilA-C, shown. Electrical conductivity of pili is much lower than that of cytochrome nanowires. Evidence suggests that PilA-NC filaments are periplasmic pseudopili crucial for exporting cytochrome nanowires onto the cell surface, rather than the pili serving as nanowires themselves.

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Touching stretches cell membranes, opening mechanosensitive ion channels, leading to sensation by the nervous system. Pictured is the transmembrane region of a similar channel in bacteria. When closed, the narrow opening is lined by hydrophobic amino acid sidechains, making it non-conductive to ions.

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