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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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by Eric Martz
A historical review on sculptures and physical models of macromolecules.

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IB Tomasic, MC Metcalf, AI Guce, NE Clark, SC Garman. J. Biol. Chem. 2010 doi: 10.1074/jbc.M110.118588
The human lysosomal enzymes α-galactosidase and α-N-acetylgalactosaminidase share 46% amino acid sequence identity and have similar folds. Using a rational protein engineering approach, we interconverted the enzymatic specificity of α-GAL and α-NAGAL. The engineered α-GAL retains the antigenicity but has acquired the enzymatic specificity of α-NAGAL. Conversely, the engineered α-NAGAL retains the antigenicity but has acquired the enzymatic specificity of the α-GAL enzyme. Comparison of the crystal structures of the designed enzyme to the wild-type enzymes shows that active sites superimpose well, indicating success of the rational design. The designed enzymes might be useful as non-immunogenic alternatives in enzyme replacement therapy for treatment of lysosomal storage disorders such as Fabry disease.

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by Eric Martz
The Ramachandran Principle says that alpha helices, beta strands, and turns are the most likely conformations for a polypeptide chain to adopt, because most other conformations are impossible due to steric collisions between atoms. Check Show Clashes to see where non-bonded atoms are overlapping, and thus in physically impossible positions.

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