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by Eric Martz
Coronavirus SARS-CoV-2 (responsible for COVID-19) has a spike protein on its surface, which enables it to infect host cells. Initially, proteases in the lungs clip the homo-trimeric spike protein at a unique sequence. This primes it, causing it to extend its receptor binding surface (shown in the above animation), optimizing binding to the host cell's ACE2 receptor (not shown). Next, spike protein initiates fusion of the virus and host cell membranes (not shown), enabling the virus RNA to enter the cell and initiate production of new virions. Knowledge of spike protein's molecular structure and function is crucial to developing effective therapies and vaccines.
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H Matsunami, YH Yoon, VA Meshcheryakov, K Namba, FA Samatey. Scientific Reports 2016 doi: 10.1038/srep27399
A periplasmic flagellar chaperone protein, FlgA, is required for P-ring assembly in bacterial flagella of taxa such as Salmonella enterica or Escherichia coli. Here we present the open and closed crystal structures of FlgA from Salmonella enterica serovar Typhimurium, grown under different crystallization conditions. An intramolecular disulfide cross-linked form of FlgA caused a dominant negative effect on motility of the wild-type strain.

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Positive (+) and Negative (-) charges on the surface of a protein molecule play crucial roles in its interactions with other molecules, and hence in its functions. Electrostatic potential maps coloring the surface of a protein molecule are a popular way to visualize the distribution of surface charges. Easy to use free software is available to to create these surface maps. Above is an integral membrane potassium channel protein. One of its 4 identical chains is removed so you can see the Negative (-) protein surface contacting the 3 K+ ions.

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