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HIV-1 protease

by David Canner
The X-ray structure of HIV-1 protease reveals that it is composed of two symmetrically related subunits which form a tunnel where they meet. This is critical because it contains the active site of the protease, consisting on two Asp-Thr-Gly conserved sequences, making it a member of the aspartyl protease family. The two catalytic Asp's either interact with the incoming water or protonate the carbonyl to make the carbon more electrophilic for the incoming water.

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Geobacter pili: surprising function.

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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Polio is still here!
Polio vaccines have been available since the 1950s, but the challenges of vaccination in remote areas of Afghanistan and Pakistan have prevented worldwide eradication. In 2022, polio was found circulating in parts of New York State, USA. The polio virus has a small RNA genome enclosed in an icosahedral capsid composed of several proteins, shown cut in half. The structures of virus capsids can be explored using free FirstGlance in Jmol.

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